Synthroid long term side effects

Synthroid Side Effects

Generic Name: levothyroxine

Medically reviewed by Last updated on Dec 18, 2018.

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Note: This document contains side effect information about levothyroxine. Some of the dosage forms listed on this page may not apply to the brand name Synthroid.

For the Consumer

Applies to levothyroxine: oral capsule liquid filled, oral tablet

Other dosage forms:

  • injection powder for solution


Oral route (Capsule; Tablet; Solution)

Thyroid hormones, including levothyroxine, should not be used either alone or with other therapeutic agents for the treatment of obesity or weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.

Along with its needed effects, levothyroxine (the active ingredient contained in Synthroid) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking levothyroxine:

Less common

  • Chest pain or discomfort
  • decreased urine output
  • difficult or labored breathing
  • difficulty with swallowing
  • dilated neck veins
  • extreme fatigue
  • fainting
  • fast, slow, irregular, pounding, or racing heartbeat or pulse
  • fever
  • heat intolerance
  • hives or welts, skin itching, rash, or redness
  • irregular breathing
  • irritability
  • menstrual changes
  • nausea
  • pain or discomfort in the arms, jaw, back, or neck
  • sweating
  • swelling of the eyes, face, lips, throat, or tongue
  • tightness in the chest
  • tremors


  • Blurred or double vision
  • dizziness
  • eye pain
  • lack or slowing of normal growth in children
  • limp or walk favoring one leg
  • pain in the hip or knee
  • seizures
  • severe headache

Get emergency help immediately if any of the following symptoms of overdose occur while taking levothyroxine:

Symptoms of overdose

  • Change in consciousness
  • cold, clammy skin
  • confusion
  • disorientation
  • fast or weak pulse
  • lightheadedness
  • loss of consciousness
  • sudden headache
  • sudden loss of coordination
  • sudden slurring of speech

Some side effects of levothyroxine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

  • Abdominal or stomach cramps
  • change in appetite
  • crying
  • diarrhea
  • false or unusual sense of well-being
  • fear or nervousness
  • feeling not well or unhappy
  • feeling of discomfort
  • feeling of warmth
  • feeling things are not real
  • feelings of suspicion and distrust
  • hair loss
  • headache
  • increased appetite
  • mental depression
  • muscle weakness
  • quick to react or overreact emotionally
  • rapidly changing moods
  • redness of the face, neck, arms, and occasionally, upper chest
  • restlessness
  • trouble getting pregnant
  • trouble sitting still
  • unusual tiredness or weakness
  • vomiting
  • weight gain or loss

For Healthcare Professionals

Applies to levothyroxine: compounding powder, injectable powder for injection, intravenous powder for injection, intravenous solution, oral capsule, oral solution, oral tablet


The more commonly reported adverse events have included those of hyperthyroidism due to therapeutic overdose including arrhythmias, myocardial infarction, dyspnea, muscle spasm, headache, nervousness, irritability, insomnia, tremors, muscle weakness, increased appetite, weight loss, diarrhea, heat intolerance, menstrual irregularities, and skin rash.


Cardiac function was evaluated in 20 patients requiring TSH suppression for either thyroid goiter or following thyroidectomy and radioactive iodine therapy for thyroid cancer and in 20 age and sex-matched controls. TSH suppression was associated with an increased incidence of premature ventricular beats, an increased left ventricular mass index, and enhanced left ventricular systolic function. The clinical significance of these changes remains to be determined.

Overtreatment with this drug may cause an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients.

Frequency not reported: Palpitations, tachycardia, hypertension, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest


Frequency not reported: Changes in symptom presentation for diabetes and adrenal cortical insufficiency

Nervous system

Frequency not reported: Headache, hyperactivity, insomnia, seizures, pseudotumor cerebri (children)


Frequency not reported: Hair loss, flushing, urticaria, pruritus, skin rash, angioedema, excessive sweating


A study evaluated the effect of long-term thyroid hormone therapy on bone mineral density in 196 women (mean age, 74.4 years) compared to a control group comprised of 795 women (mean age, 72.1 years). The mean daily thyroxine dose was 1.99 mcg/kg (range, 0.3 to 6.6 mcg/kg) with a mean duration of therapy of 20.4 years (range, less than 1 to 68 years). Women taking daily doses of 1.6 mcg/kg or more had significantly lower bone mineral density levels at the ultradistal radius, midshaft radius, hip, and lumbar spine compared to controls. However, estrogen use appeared to negate the adverse effects of thyroid hormone on bone mineral density.

Higher rates of femur fractures have been found in males (p=0.008) prescribed long-term thyroid hormone therapy as compared to controls in a case-control analysis of 23,183 patients, from the United Kingdom General Practice Research Database, prescribed thyroid hormone.

Overtreatment may result in craniosynostosis in infants and premature closure of the epiphyses in children with resultant compromised adult height.

Frequency not reported: Tremors, muscle weakness, muscle cramps, increased risk of osteoporosis, slipped capital femoral epiphysis (children)


Frequency not reported: Diarrhea, vomiting, abdominal cramps


Frequency not reported: Menstrual irregularities, impaired fertility


Hypersensitivity reactions have occurred; however, it has been attributed to the inactive ingredients. These reactions have included urticaria, pruritus, skin rash, flushing, angioedema, various GI symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness and wheezing. Hypersensitivity to levothyroxine (the active ingredient contained in Synthroid) itself is not known to occur.

Frequency not reported: Serum sickness, hypersensitivity to inactive ingredients


Frequency not reported: Increased appetite, weight loss


Frequency not reported: Autoimmune disorders (e.g., chronic autoimmune thyroiditis)


Frequency not reported: Fatigue, heat intolerance, fever


Frequency not reported: Nervousness, anxiety, irritability, emotional lability

3. “Product Information. Synthroid (levothyroxine).” Abbott Pharmaceutical, Abbott Park, IL.

4. Cerner Multum, Inc. “UK Summary of Product Characteristics.” O 0

5. Sheppard MC, Holder R, Franklyn JA “Levothyroxine treatment and occurrence of fracture of the hip.” Arch Intern Med 162 (2002): 338-43

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

Related questions

  • Effect of not taking medicine after thyroid removal?

Medical Disclaimer

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Consumer resources

  • Synthroid
  • Synthroid (Advanced Reading)
  • Synthroid Injection (Advanced Reading)

Other brands: Levoxyl, Tirosint, Euthyrox, Levothroid, … +2 more

Professional resources

  • Synthroid (FDA)
  • … +1 more

Related treatment guides

  • Hashimoto’s disease
  • Hypothyroidism, After Thyroid Removal
  • Underactive Thyroid
  • TSH Suppression
  • Thyroid Suppression Test
  • Myxedema Coma

Synthroid (levothyroxine) is the most commonly prescribed medication in the US, and is used to treat hypothyroidism—often for a lifetime. Symptoms of hypothyroidism, or under-active thyroid, may include fatigue, weight loss, anxiety and depression. Here are seven questions I get asked a lot about levothyroxine and thyroid hormone replacement therapy.

What is Synthroid (levothyroxine)?

Synthetic thyroxine (T4) comes as brand-name Synthroid or generic levothyroxine. T4 is what is known as a “prohormone”; it’s made by the thyroid gland and gets converted to the active hormone, T3, in other body tissues. The advantage to taking T4 over T3 is that your own body’s mechanisms can control how quickly T4 is converted to T3.

What’s the difference between levothyroxine and Synthroid?

Generic levothyroxine may differ slightly from Synthroid in terms of how well it’s absorbed. That’s why it’s preferable to stick with either one if possible. Both the American Thyroid Association and the Endocrine Society recommend that patients remain on Synthroid if that’s what was initially prescribed. If you are on generic levothyroxine, try to stick with the same generic manufacturer—your pharmacist can help you with that.

What about switching from Synthroid to a desiccated thyroid extract like Armour Thyroid? Many studies have compared Synthroid to desiccated thyroid extract and revealed no differences in symptoms and neurocognitive measurements between the two groups.

Levothyroxine dosage and how to take it

The average replacement dose of T4 in adults is approximately 1.6 mcg/kg per day, which would be 112 mcg per day in a 70-kg adult, but this is not a one-size-fits-all recommendation.

Synthroid should be taken on an empty stomach, ideally an hour before breakfast. Another option is to take it at bedtime if you’ve had nothing to eat for several hours. High-fiber diets, coffee, and iron and calcium supplements can interfere with levothyroxine absorption by up to 30%.

Be careful if you take other medications. People on estrogen therapy may need to up their levothyroxine dosage. And proton pump inhibitors like omeprazole and Nexium can limit levothyroxine absorption.

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TSH blood tests

A TSH (thyroid stimulating hormone) blood test tells doctors whether or not your thyroid hormones are back to normal. Patients who are treated with T4 usually begin to see symptoms improve within two weeks, but complete recovery can take at least six weeks. At six week, a TSH blood test should be performed. Once TSH levels in patients with primary hypothyroidism return to reference range, periodic monitoring is warranted.

What are normal TSH blood test results?

There’s plenty of controversy here. Most labs consider normal TSH levels to be under 4.5 to 5.0 mU/L, but some argue that the upper limit of normal range should be reduced to 2.5 mU/L. That’s because most “normal thyroid” volunteers have TSH blood values between 0.4 and 2.5 mU/L.

The aim should be to keep TSH within normal reference range (about 0.5 to 5.0 mU/L), but if you continue to have hypothyroid symptoms, talk to your doc about whether you should increase your dose of levothyroxine and aim for a TSH value in the lower half of the normal range (0.4 to 2.5 mU/L).

Side effects of too much levothyroxine

One potential effect of too much levothyroxine that might seem nice is weight loss, but over-replacement with thyroid therapy so your TSH levels become too low is a bad idea—and I see it all the time.

The main risk is atrial fibrillation, a dangerous heart rate abnormality, which occurs three times more often in patients who are on too much levothyroxine. You may also have accelerated bone loss and therefore, a higher risk of fractures.

Therapy with additional liothyronine (T3)

Some folks on levothyroxine with normal TSH levels still experience hypothyroidism symptoms. In fact, 9% to 13% of people taking Synthroid with normal TSH values still report impaired psychological well-being.

Combination therapy is an area of controversy. Here’s what the science says: Years of studies comparing T4 alone to T4 plus T3 (Cytomel) show that the latter is not superior to T4 alone in managing symptoms of hypothyroidism.

Hope that helps.

Dr O.

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  • Finding the correct dosage of this thyroid hormone isn’t always easy and the side effects are difficult: Take too little Synthroid and your symptoms of weight gain, fatigue and depression won’t go away. Take too much and you’re at risk for weak bones, insomnia, breathlessness and even heart problems.

    My own experience with Synthroid began a few years ago when I started feeling more tired than usual. I chalked it up to stress, my endless to-do list and the lack of sleep. A blood test, however, revealed that I had hypothyroidism. That meant my thyroid wasn’t churning out enough thyroid hormone. So I became a member of what my friend MJ calls the Synthroid Society and began taking a small dosage of levothyroxine, the generic version of Synthroid and a synthetic form of thyroid hormone.

    According to the National Institutes of Health, nearly 5% of Americans age 12 and over suffer from hypothyroidism. Because the symptoms mimic those of other conditions, experts believe many people are undiagnosed. In fact, the American Thyroid Association estimates that including mild cases, hypothyroidism actually affects up to 15% of Americans.

    How the Thyroid Gland Works

    Think of the thyroid as your body’s internal thermostat. This small bow-tie shaped gland is a power player in the body, one that has the potential to inflict a lot of chaos and confusion. It regulates your heart rate, metabolism, gastrointestinal function, menstrual cycle, mood, respiration and virtually every other function in the body.

    When your body doesn’t make enough thyroid hormone, everything slows down, and you develop hypothyroidism. Symptoms vary. Some people gain weight, suffer depression or develop dry skin and nails. Others experience constipation, a foggy brain and chronic fatigue. Women may notice that their periods are heavier and more frequent, and that it may be difficult to get pregnant.

    Too much thyroid hormone causes hyperthyroidism and has the opposite effect. This condition makes you anxious and irritated, and you may lose weight, have trouble sleeping and suffer diarrhea. It can also cause heart palpitations and weak bones. Hyperthyroidism is much less common than hypothyroidism and affects only about 1% of the population.

    When the Thyroid Slows

    Hypothyroidism is caused by several different disorders. For most people, it’s the result of an autoimmune disease called Hashimoto’s disease, which causes thyroiditis, or inflammation of the thyroid gland. Others develop hypothyroidism when they suffer thyroiditis due to the use of certain medications such as interferon or amiodarone, or when they undergo the surgical removal of the thyroid due to problems such as thyroid cancer. Some people simply develop hypothyroidism with age.

    Women are much more likely than men to develop hypothyroidism. The condition is more common after age 50, but can occur in children as well. It is also more common in people who have autoimmune diseases and is a certain result of thyroid cancer or any other condition that requires the surgical removal of your thyroid.

    Hypothyroidism often goes undiagnosed because the symptoms resemble those of other problems. If you’re tired, you might blame your late nights at the office. Gaining weight? Could be those late night snacks. Depression? Chalk that up to your volatile marriage. But in reality, any of these symptoms could be hypothyroidism.

    Treating Hypothyroidism

    Detecting hypothyroidism is fairly simple. All you need is a blood test that measures levels of thyroid stimulating hormone (TSH), which is what your pituitary gland produces when your thyroid isn’t making enough thyroid hormone. High TSH levels means your pituitary is signaling your thyroid to secrete more, once prescribed, thyroid hormone. Treatithe rest of your ng hypothyroidism requires you to replace the thyroid hormone your body normally makes. Synthroid is what experts call true hormone replacement therapy because you are using medicine to replace what your body no longer makes but should be making. Synthroid is generally taken for life.

    Before taking Synthroid or the generic levothyroxine, you should notify your doctor about any medical conditions you have, such as heart disease or diabetes, and any medications you take. It used to be thought that certain medications such as anticoagulants (warfarin) can become more potent in the presence of Synthroid, however recent research has shown that there is no interaction between Synthroid and warfarin. Insulin or sulfonylureas for diabetes may become more or less effective. Antacids that contain aluminum, magnesium, simethicone or calcium, such as Gaviscon, Maalox, Mylanta, Gas-X or Rolaids, can make Synthroid less effective. The same is true of sucralfate (Carafate), which is prescribed for peptic ulcers. Iron can also interfere with the absorption of Synthroid. If you need to take these medications or supplements, take them four hours before or after you take Synthroid. You should also point out to your doctor if you are trying to get pregnant or are breastfeeding.

    A significant number of Synthroid users find they have to ask their doctors to adjust their dosage. It’s important, therefore, that those on this thyroid hormone monitor whether they are having any side effects from the medicine and whether their original symptoms are abating. Luckily for me, my initial dosage has worked well. A follow-up blood test six weeks after I started Synthroid showed my TSH levels were back to normal.

    Many people aren’t so lucky. Consider my friend MJ who spent years trying to figure out why she felt so anxious and tired. Doctors eventually determined she was taking too much Levoxyl, another synthetic thyroid hormone treatment, and it was making her jumpy and wearing her out. Reducing the dosage helped, but she’s worried how the extra Levoxyl all those years may have affected her bones.

    And it turns out that for those with the early signs of underactive thyroid, or subclinical hypothyroidism, taking thyroid hormone medication doesn’t help to treat symptoms or improve quality of life. According to a study reported in JAMA, researchers conducted a meta-analysis of 21 clinical trials that enrolled 2,200 people with subclinical hypothyroidism. In those trials, participants received either a thyroid hormone drug (levothyroxine in most of the trials), a placebo or no treatment at all. Hormone treatment was not associated with a benefit in terms of improved quality of life or a reduction in hypothyroid symptoms. Thyroid hormone drugs also did not lead to improvement in terms of depressive symptoms, cognitive functions, muscle strength and blood pressure. The study authors also note that “thyroid hormone therapy is associated with adverse effects when overtreatment occurs.” Overtreatment caused MJ to feel jumpy and worn out, and other adverse effects can include fast heart rate, excessive sweating and weight loss.

    Meanwhile, my friend Cheryl spent years trying to figure out why her TSH levels are so high when she’s already taking a relatively high dose of Synthroid. Should she instead take Armour, which is a thyroid hormone extracted from pig thyroids? Ultimately, what worked for her was taking levothyroxine with aqueous selenium and liquid iodine. Last year, she began taking the selenium and iodine every other day. Iodine is essential to the production of thyroid hormone, while selenium helps the body convert T4, the inactive form of thyroid hormone into T3, the active form.

    Be Smart With Synthroid

    If you have hypothyroidism, taking Synthroid needs to become a part of your daily routine. To keep blood levels on an even keel, you should also take it at the same time every day.

    Ideally, you should take Synthroid on an empty stomach since food can delay absorption. Me? I take it in the middle of the night, when I know I won’t be eating anything. In fact, it’s best to wait an hour after taking your pill before eating. Certain foods can inhibit absorption of Synthroid, too. A diet rich in fiber for instance, may decrease the amount your body absorbs.

    Foods such as soy and grapefruit juice, and supplements like calcium and iron can also interfere with absorption. If you must eat these foods or take these supplements, make sure to wait at least four hours after taking your medication before doing so.

    The good news is that Synthroid doesn’t usually cause serious side effects or stress on the kidneys or liver. Although some hair loss can be a side effect in the first few months of treatment, most of the time Synthroid improves hair growth. Any side effects are usually the result of overdosage. In 2011, I coauthored the book The Everything Guide to Thyroid Disease with Theodore C. Friedman, MD, PhD, an endocrinologist and chief of endocrinology, molecular medicine and metabolism at Charles R. Drew University of Medicine and Science in Los Angeles. According to Dr. Friedman, “Too much thyroid medication can lead to heart problems, weight loss, osteoporosis and symptoms of hyperthyroidism including palpitations and nervousness.” Too much thyroid hormone in the blood can put a person at risk for having a bone fracture or a heart arrhythmia. If someone has heart problems, it can also lead to a heart attack. For these reasons, you should never take a higher dosage of thyroid hormone for the purpose of losing weight.

    Knowing whether you need to adjust your dosage is a matter of being vigilant about how you feel. It’s important to note whether you’re gaining weight for no good reason, feeling more tired than usual or are suddenly inexplicably depressed. If you notice these or any new symptoms, you should talk to your doctor about adjusting your dosage.

    Buying Synthroid

    Most people, including me, get their Synthroid from their local drugstore or a mail-order pharmacy. But if you want to buy Synthroid online, make sure to get a prescription from your doctor and use a licensed pharmacy, which means you’ll have access to a licensed pharmacist in case you have questions. Dr. Friedman echoes this advice and encourages patients to read the site’s privacy and security policies to ensure their information is kept private. In addition, he recommends that you always ask for Synthroid and not its generic version, levothyroxine.

    Other Options

    While levothyroxine, the generic of Synthroid is the drug of choice for people with hypothyroidism, patients do have other treatment options. Many alternative doctors prescribe Armour because it comes from the thyroids of pigs and is believed by some to be more natural and more similar to human thyroid hormone. But many traditional doctors favor Synthroid, believing that synthetic is best, says Dr. Friedman. Since some patients may do better on Armour, however, Dr. Friedman recommends talking to your doctor about trying Armour if you are not feeling well on Synthroid.

    Although most patients do just fine taking Synthroid, some do better if they also take T3, the active form of thyroid hormone. Synthroid is comprised of thyroxine, or T4, which is converted into T3 in the body. About 5% to 10% of people taking T4 still have bothersome hypothyroid symptoms. For these patients, adding T3 or Cytomel, to their treatment regimen may help.

    For more than 60 years, levothyroxine has been used by millions of Americans. In fact, according to the IQVIA Institute for Human Data Science, 96 million prescriptions were written for generic Synthroid in 2018.

    The key to successful use of Synthroid seems to be in the monitoring of the dosage you receive. Keeping close tabs on any changes in how you feel on Synthroid and working with your doctor to make sure your dosage is correct can go a long way in using this ubiquitous thyroid medication successfully.

    Winnie Yu is a nationally known writer and author, and coauthor of The Everything Guide to Thyroid Disease.

    Is There a Substitute for Levothroid?

    Q1. I have been taking Levothroid for many years. Is there any substitute for this medication, natural or otherwise? I’ve tried to stop taking this drug several times, but my creatine levels get thrown out of whack. I am trying to rid myself of any kind of drugs because of their possible side effects.

    Unfortunately, the simple answer is no, there is no substitute for this medicine. Thyroid hormone is critical to many important bodily functions, including metabolism, growth, and development. The thyroid hormone that you are taking, levothyroxine (the generic name for the drug Levothroid), replaces what your thyroid is unable to make naturally. As you already noted, if you stop taking this medication it can result in other medical problems; sometimes it can even lead to life-threatening situations.

    One thing that your doctor should already be doing is monitoring your thyroid-stimulating hormone (TSH) and T4 levels so that your levothyroxine dose can be adjusted appropriately. This way, excessive levels of thyroid hormone and the resulting side effects can be avoided or minimized.

    Q2. I’ve been taking .50 mcg Synthroid for thyroid disease for more than 20 years. What are the possible effects this long-term use will have on my body?

    — Aramentis, New York

    Synthroid regulates thyroid function and controls hypothyroidism. Its untoward side effects are related to both the level and the duration of dosage, so it’s best to use the smallest dose that does the job.

    There has been concern about long-term use of Synthroid causing bone thinning or osteoporosis. Postmenopausal women on long-term Synthroid therapy are at the highest risk, since they start out with less bone than men and have lost the protective effect of estrogen, but premenopausal women and men may also lose bone density as well.

    To minimize the potential for bone loss, your doctor should prescribe the lowest dosage needed to control symptoms of thyroid deficiency. It is useful to have bone density tests to check for changes, particularly if you are over 50. Ask your doctor about getting a bone density test, if you haven’t already had one.

    Q3. I am 72 and my doctor recently told me I have antibodies in my thyroid that shouldn’t be there and I might need to take thyroid hormones. She plans to check again in 6 months. What can you tell me about thyroid hormones? Are there any side effects associated with replacement therapy?

    It sounds as though your doctor is concerned that your thyroid gland may be becoming underactive, a condition medically known as hypothroidism. Thyroid hormones play important roles in regulating a number of functions in the body, including metabolism, heart rate, and blood pressure. It is necessary that a sufficient amount of thyroid hormones be available in your blood for your body to successfully perform these functions. When hormones levels are too low, people often feel tired or depressed, and have little toleration for the cold.

    Hypothyroidism is diagnosed based on tests that measure the level of thyroid hormones and serum TSH (thyroid stimulating hormone) in the blood. It sounds as though your doctor is planning to repeat these tests in 6 months. Then, along with a physical examination and a discussion of how you’re feeling, your doctor will have a much better idea about whether to prescribe thyroid hormone replacement therapy for you.

    When taken properly, this type of therapy is generally safe and well-tolerated. This means starting with a low dose and gradually building up to the proper level as well as following up carefully with physical examinations and blood tests. If you currently have any problems with your heart, such as an irregular heart beat, it is important that you and your doctor be especially careful in monitoring your health if you start to take thyroid hormones.

    Learn more in the Everyday Health Thyroid Conditions Center.


    How does this medication work? What will it do for me?

    Levothyroxine is a thyroid hormone supplement used to treat people who do not produce enough thyroid hormone on their own. Levothyroxine helps to reduce the symptoms of low thyroid hormone such as weight gain, sensitivity to cold, lack of energy, and dry skin. It may take several weeks for this medication to have a noticeable effect on your condition.

    This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

    Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are being given this medication, speak to your doctor. Do not stop using this medication without consulting your doctor.

    Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to use this medication if their doctor has not prescribed it.

    What form(s) does this medication come in?

    25 µg
    Each orange, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 25 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and talc.

    50 µg
    Each white, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 50 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, lactose, magnesium stearate, povidone, and talc.

    75 µg
    Each violet, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 75 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, FD&C Blue No. 2, FD&C Red No. 40, lactose, magnesium stearate, povidone, and talc.

    100 µg
    Each yellow, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 100 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, D&C Yellow No. 10, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and talc.

    112 µg
    Each rose, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 112 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, D&C Red No. 27, D&C Red No. 30, lactose, magnesium stearate, povidone, and talc.

    137 µg
    Each turquoise, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 137 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, FD&C Blue No. 1, lactose, magnesium stearate, povidone, and talc.

    150 µg
    Each blue, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 150 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, FD&C Blue No. 2, lactose, magnesium stearate, povidone, and talc.

    200 µg
    Each pink, round, colour-coded, scored tablet, debossed with “SYNTHROID” on one side and potency on the other side contains levothyroxine sodium, USP 200 µg. Nonmedicinal ingredients: acacia, confectioner’s sugar, FD&C Red No. 40, lactose, magnesium stearate, povidone, and talc.

    How should I use this medication?

    The dose of levothyroxine depends on how much of the hormone is needed to bring blood levels back to the normal range. This is determined by blood tests that are done in a laboratory. The starting dose will depend on your general physical condition and the severity and length of time that you have been experiencing symptoms of low thyroid hormone levels.

    You should take this medication once a day at the same time every day to ensure a consistent effect. Cotton seed meal, dietary fiber, soybean flour (infant formula), or walnuts may decrease the absorption of levothyroxine.

    Signs that you may be getting too much thyroid hormone may include chest pain, increased heart rate, palpitations, excessive sweating, heat intolerance, and nervousness. If you think your dose of thyroid hormone may be too high, consult your doctor as soon as possible.

    Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones given here, do not change the way that you are using the medication without consulting your doctor.

    It is important to take this medication exactly as recommended by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

    Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

    Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

    Who should NOT take this medication?

    Do not take this medication if you:

    • are allergic to levothyroxine or any ingredients of the medication
    • are having a heart attack
    • have acute thyrotoxicosis (too much thyroid hormone in their system)
    • have uncorrected adrenal insufficiency

    What side effects are possible with this medication?

    Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

    The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

    The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

    Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

    • diarrhea
    • fever
    • hair loss (temporary; particularly in children during the first month of treatment)
    • headache
    • increased appetite
    • increased sweating
    • menstrual cycle changes
    • nervousness or irritability
    • sensitivity to heat
    • stomach cramps
    • tremor (shaking)
    • trouble sleeping
    • upset stomach
    • weight loss

    Although most of these side effects listed below don’t happen very often, they could lead to serious problems if you do not seek medical attention.
    Stop taking the medication and seek immediate medical attention if any of the following occur:

    • chest pain, irregular heartbeat, or shortness of breath
    • severe allergic reaction (e.g., hives; difficulty breathing; wheezing; or swelling of the eyes, mouth, or lips)
    • vomiting

    Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

    Are there any other precautions or warnings for this medication?

    Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

    Bone density: Levothyroxine can cause bones to lose thickness. If you have an increased risk for osteoporosis (bone thinning) or are taking medications that reduce bone thickness (e.g., prednisone or antiseizure medications), before you start taking this medication, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

    Your doctor may monitor your bone thickness while you are taking this medication.

    Diabetes: Levothyroxine raises blood sugar levels. For people with diabetes, this may result in an increase in the requirements for insulin or antidiabetes medications. If you have diabetes or are at an increased risk of developing diabetes, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

    You may need to monitor your blood sugar more closely when starting this medication or changing doses of this medication.

    Heart disease: When starting levothyroxine, people with heart disease may be started on a lower dosage as it may cause the heart to work harder than it has been used to. If you have heart disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

    Signs of getting too much or too little medication: Contact your doctor as soon as possible if you notice any signs of getting too much medication (such as chest pain, confusion, fast or irregular heartbeat, mood swings, muscle weakness, psychosis, extreme restlessness, yellow eyes or skin, or shortness of breath) or signs of not getting enough medication (such as clumsiness, coldness, constipation, dry, puffy skin, listlessness, muscle aches, sleepiness, tiredness, weakness, or weight gain).

    Weight loss: Levothyroxine should not be used for weight loss. Large doses of levothyroxine can cause serious ore even life threatening side effects especially when taken together with other medications for weight loss.

    Pregnancy: Levothyroxine should be taken throughout pregnancy to regulate the levels of thyroid hormone for the pregnant mother and the developing baby. If you become pregnant while taking this medication, contact your doctor as soon as possible. Your doctor may want to monitor your thyroid function more closely while you are pregnant.

    Breast-feeding: Only a small amount of thyroid hormone is passed into breast milk. The use of appropriate amounts of this medication by breast-feeding women has not been shown to cause harm for breast-fed babies.

    Seniors: Seniors may be more sensitive to the effects of levothyroxine.

    What other drugs could interact with this medication?

    There may be an interaction between levothyroxine and any of the following:

    • amiodarone
    • antacids (e.g., aluminum hydroxide, calcium carbonate, magnesium hydroxide)
    • anticonvulsants (e.g., carbamazepine, phenytoin, phenobarbital)
    • beta-blockers (e.g., metoprolol, propranolol)
    • birth control pills containing estrogen
    • calcium carbonate
    • calcium polystyrene sulfonate
    • cholestyramine
    • ciprofloxacin
    • colesevelam
    • colestipol
    • corticosteroids (e.g., dexamethasone, hydrocortisone, prednisone)
    • diabetes medications (e.g., chlorpropamide, glipizide, glyburide, insulin, metformin, nateglinide, rosiglitazone)
    • diazepam
    • diet pills
    • digoxin
    • estrogens (e.g., conjugated estrogen, estradiol, ethinyl estradiol)
    • iron supplements (e.g., ferrous fumarate, ferrous gluconate,ferrous sulfate)
    • lithium
    • magnesium supplements (e.g., magnesium hydroxide, magnesium oxide)
    • maprotiline
    • methimazole
    • multivitamins/minerals with iron, folic acid.
    • octreotide
    • nicotinic acid
    • orlistat propylthiouracil
    • rifampin
    • selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, duloxetine, fluoxetine, paroxetine, sertraline)
    • sevelamer
    • simethicone
    • sodium polystyrene sulfonate
    • certain statins (e.g., lovastatin, simvastatin)
    • sucralfate
    • sulfonamide antibiotics (“sulfas”; e.g., sulfisoxazole, sulfamethoxazole)
    • sympathomimetic medications (e.g., amphetamines)
    • theophyllines (e.g., aminophylline, oxtriphylline, theophylline)
    • tamoxifen
    • thiazide diuretics (e.g., hydrochlorothiazide)
    • tricyclic antidepressants (e.g., amitriptyline, imipramine)
    • warfarin

    If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

    • stop taking one of the medications,
    • change one of the medications to another,
    • change how you are taking one or both of the medications, or
    • leave everything as is.

    An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

    Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

    All material copyright MediResource Inc. 1996 – 2020. Terms and conditions of use. The contents herein are for informational purposes only. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Source:

    5 Natural Remedies for Hypothyroidism

    The standard treatment for hypothyroidism is taking daily thyroid hormone replacement medication. Of course, medicines often come with side effects, and forgetting to take a pill might lead to more symptoms. In some cases, natural remedies may cause fewer side effects and fit into your overall lifestyle better.

    Natural Remedies

    The goal of natural remedies or alternative medicine is to fix the root cause of the thyroid problem. Thyroid problems sometimes start as the result of poor diet, stress, or missing nutrients in your body. Changing your diet and taking an herbal supplement are two ways you can help your thyroid condition. These options may have fewer side effects than taking thyroid medicine. Also, using an herbal supplement for treatment of a low or underactive thyroid may be helpful for people who aren’t responding well to medicines.

    Consider the following five natural remedies as additions or alternatives to your treatment plan.


    According to the National Institutes of Health (NIH), selenium is a trace element that plays a part in thyroid hormone metabolism. Many foods on the market today contain selenium, including grass-fed beef, tuna, turkey, and Brazil nuts.

    Hashimoto’s thyroiditis, an immune system attack on the thyroid, often diminishes the body’s selenium supply. Supplementing this trace element has shown to help balance thyroxine, or T4, levels in some people. It’s important to talk with your doctor about how much selenium may be right for you since every person is different.

    Sugar-Free Diet

    Sugar and processed foods can lead to increased inflammation in the body. Inflammation can slow down the conversion of T4 to triiodothyronine, or T3, another thyroid hormone. This can make your symptoms and thyroid disease worsen.

    Also, sugar only boosts your energy level in the short term, eliminating it from your diet may help regulate your energy levels. Additionally, removing sugar from your diet may help your skin and stress levels. It’s not easy to adopt a sugar-free diet, but the benefit to your thyroid health may be worth it.

    Vitamin B

    Taking certain vitamin supplements can have an impact on your thyroid health. Low thyroid hormones can affect your body’s vitamin B-12 levels. Taking a vitamin B-12 supplement may help you repair some of the damage your hypothyroidism caused.

    Vitamin B-12 can help with the tiredness caused by thyroid disease. Thyroid disease also impacts your vitamin B-1 levels. You can add more B vitamins to your diet with the following foods:

    • peas
    • asparagus
    • sesame seeds
    • tuna
    • cheese
    • milk
    • eggs

    Vitamin B-12 is generally safe for most healthy individuals at recommended levels. The vitamin should be used with caution if you have any of the following conditions:

    • heart disorder
    • high blood pressure
    • history of cancer
    • skin disorders
    • discolored urine
    • stomach issues
    • anemia, due to abnormal potassium levels
    • blood clotting disorders
    • increased uric acid or gout

    It’s important to talk with your doctor about how much vitamin B-12 may be right for you.


    The NIH studied the link between hypothyroidism and small intestine problems. These problems included an overgrowth of bacteria, such as yeast. Probiotic supplements contain live bacteria that can help keep your stomach and intestines healthy. Besides supplement forms, fermented food and drink, such as kefir, kombucha, raw cheese, and yogurt contain useful probiotics.

    However, the Food and Drug Administration has not approved the use of probiotics for the prevention or treatment of any condition. Talk with your doctor to see if these supplements might help you.

    Gluten-Free Diet

    Adopting a gluten-free diet is more than a fad for many people with hypothyroidism. According to the National Foundation for Celiac Awareness, a significant number of people with thyroid disease also have celiac disease, which is a digestive disorder in which people cannot handle consuming gluten.

    While research doesn’t currently support a gluten-free diet for the treatment of thyroid disease, many people with Hashimoto’s thyroiditis and hypothyroidism do feel better after cutting wheat and other gluten containing foods from their diet.

    But there are some drawbacks to going gluten free. For one, the cost of buying gluten-free foods is often much higher than foods containing wheat. And some prepackaged, gluten-free foods aren’t healthy. That’s because these foods often have a higher fat content and less fiber than wheat containing products.

    The Takeaway

    For many, the advantages of adopting a natural thyroid treatment plan outweigh the disadvantages. However, if you’ve had surgery to remove your thyroid, a natural thyroid treatment plan isn’t for you. As always, you should discuss any treatment plans with your doctor before starting them.

    Ask the experts

    What is your feeling regarding natural vs. synthetic replacement therapy in hypothyroid situations? Armour, for example vs. Synthroid? My daughter is exceedingly sensitive to most medications and is in the process of being diagnosed for possible Hashimoto’s.

    Doctor’s response

    While it is reasonable to assume that synthetic medications are less desirable than natural counterparts, in this case- natural thyroid hormone replacement is definitely not an ideal solution for the vast majority of people.

    Here’s why:

    Armour thyroid is derived from desiccated pig (porcine) thyroid gland. A number of years ago, these natural preparations were our only alternative. Replacement with desiccated thyroid creates dosing problems because there is no way to standardize the exact amount of the dose for each batch. As a matter of fact, these preparations do not report their dosage strength in milligrams, but rather, in grains of thyroid. This is because, they don’t really know the milligram equivalent in each dose. Dosing is also based on the assumptions that each gland has equal amounts of hormones as the next gland, and that the ratio of T4 and T3 (the more active hormone) are similar and constant in each gland from the pigs. There is no way to be certain of this, and patients on these preparations often have fluctuating hormone levels, which may or may not result in symptoms.

    Regardless of symptoms, the goal of replacement therapy is to keep the hormone levels as stable as possible. This is much easier to achieve with synthetic preparations such as Levoxyl and Synthroid. These preparations come in a vast number of standardized doses, allowing for minute adjustments in hormone dosing. There is another comment that should be made. With all the issues surrounding “mad cow disease” and other ailments, I personally am reluctant to offer animal based therapy to patients when a safe effective well studied synthetic preparation is widely available.

    I hope this helps answer any questions you may have.

    Thank you for your question.

    Medical Author: Ruchi Mathur, M.D.



    Synthroid, also called Levothyroxine, is a synthetic thyroid produced by Knoll Pharmaceuticals. Synthroid is hormone replacement used to treat hypothyroidism, a condition in which the thyroid gland does not produce enough hormones. Synthroid is also used to treat or prevent goiter, or an enlarged thyroid gland. This can be caused by hormonal imbalances, radiation treatment, surgery or cancer. Synthroid can cause many side effects, leading some patients to seek natural alternatives.


    The consumer information provided by warns that people that have had a heart attack, a thyroid disorder called thyrotoxicosis or adrenal gland problems not controlled by treatment should not take Synthroid. An overdose of Synthroid could cause chest pain, pounding heartbeat, tremors, shortness of breath, leg cramps, confusion, vomiting, diarrhea or seizures. Allergy to Synthroid could cause hives, difficulty breathing, and swelling of the face, lips, tongue or throat. Other side effects include headache, insomnia, nervous or irritable feelings, fever, hot flashes, sweating, changes in menstrual periods, and appetite and weight changes.

    Iodine Deficiency

    If you are deficient in iodine, the University of Maryland Medical Center (UMMC) says you may be able to treat hypothyroidism by simply using iodized salt. Other natural sources of iodine include seafood and plants that are grown in iodine-rich soil. Kelp is one of the most well-known natural supplements used to increase iodine intake.

    Dietary Changes

    According to the UMMC, there are some things you can do with diet and supplements to help reduce the symptoms of hypothyroidism. Eat a diet high in B vitamins and include plenty of fresh vegetables and sea vegetables such as kelp. Eat antioxidant-rich foods, including fruits and vegetables. Get protein from cold-water fish, lean meats or beans, and avoid red meat. Exercise for 30 minutes daily.

    Eliminate suspected food allergens. Avoid refined foods, trans-fatty acids, and alcohol and tobacco use. Avoid broccoli, cabbage, Brussels sprouts, cauliflower, kale, spinach, turnips, soybeans, peanuts, linseed, pine nuts, millet, cassava and mustard greens as they are known to interfere with thyroid function.


    UMMC recommends several natural supplements to improve the symptoms of hypothyroidism. Vitamins A, B-complex, C and E, magnesium, calcium, zinc, selenium, omega-3 fatty acids, alpha-lipoic acid and L-tyrosine are recommended. Herbal supplements include bladderwrack, green tea, coleus and guggul. Consult a health care provider that is educated in natural alternatives to determine what will work best for you.

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