What happens if I miss my thyroid medication for a week?


Before taking thyroid,

  • tell your doctor and pharmacist if you are allergic to thyroid, any other medications, pork, or any of the ingredients in thyroid tablets. Ask your pharmacist for a list of the ingredients.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, and nutritional supplements you are taking or plan to take. Be sure to mention any of the following: androgens such as danazol or testosterone; anticoagulants (‘blood thinners’) such as warfarin (Coumadin);antidepressants; aprepitant (Emend); carbamazepine (Carbatrol, Epitol, Tegretol);diabetes medications that you take by mouth;, digoxin (Lanoxin); efavirenz (Sustiva); estrogen (hormone replacement therapy) griseofulvin (Fulvicin, Grifulvin, Gris-PEG); human growth hormone (Genotropin); insulin; lovastatin (Altocor, Mevacor); nevirapine (Viramune); oral contraceptives containing estrogen; oral steroids such as dexamethasone (Decadron, Dexone, Dexpak), methylprednisolone (Medrol), and prednisone (Deltasone); phenobarbital (Luminal, Solfoton); phenytoin (Dilantin, Phenytek); potassium iodide (contained in Elixophyllin-Kl, Pediacof, KIE); rifabutin (Mycobutin); rifampin (Rifadin, Rimactane, in Rifamate); ritonavir (Norvir, in Kaletra);salicylate pain relievers such as aspirin and aspirin-containing products, choline magnesium trisalicylate, choline salicylate (Arthropan), diflunisal (Dolobid), magnesium salicylate (Doan’s, others), and salsalate (Argesic, Disalcid, Salgesic); strong iodine solution (Lugol’s Solution);and theophylline (Elixophyllin, Theolair, Theo-24, Quibron, others).
  • if you take cholestyramine (Questran) or colestipol (Colestid), take it at least 4 hours before taking your thyroid medication. If you take antacids, iron-containing medications or nutritional supplements, simethicone, or sucralfate (Carafate), take them at least 4 hours before or 4 hours after taking your thyroid medication.
  • tell your doctor what herbal products you are taking, especially St. John’s wort.
  • tell your doctor if you have or have ever had diabetes; osteoporosis; hardening or narrowing of the arteries (atherosclerosis); cardiovascular disease such as high blood pressure, high blood cholesterol and fats, angina (chest pain), arrhythmias, or heart attack; malabsorption diseases (conditions that cause a decrease in absorption from the intestine); an underactive adrenal or pituitary gland; or kidney or liver disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking thyroid, call your doctor.
  • talk to your doctor about the risks and benefits of taking thyroid if you are 65 years of age or older. Older adults should not usually take thyroid becasue it is not as safe as other medications that can be used to treat the same condition.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking thyroid.

Levothyroxine drugs — Levothyroxine drugs like Synthroid, Levoxyl, and Tirosint are a synthetic version of thyroxine (T4) and are used to treat hypothyroidism.

Most experts agree that if you miss a dose of levothyroxine, you should take it as soon as you remember. If it’s been a full day since you forgot your pill, it’s still considered safe to take a double dose to “catch up.” Dr. Morris explains:

It generally works fine to take two levothyroxine tablets the day after missing one. This is because of the long half-life of T4 (seven days) and the relatively minor changes in levels that occur after taking the tablets — even two. In rare and difficult situations, where patients are unable to take medications daily or regularly (due to mental illness, for example), there have been studies that have demonstrated that it works reasonably to take seven tablets once per week if needed. (This is not our advice, but it does demonstrate the very long duration of action and half-life of this medication).

T3 Drugs — There are two types of T3 drugs: liothyronine and natural desiccated thyroid (NDT). Liothyronine drugs like Cytomel and compounded, time-released liothyronine are synthetic versions of triiodothyronine (T3) and are used — usually along with a levothyroxine drug — to treat hypothyroidism. NDT drugs like Nature-throid, Armour Thyroid, and WP Thyroid are natural drugs, derived from the dried thyroid glands of pigs, that contain natural forms of T4 and T3, and are also used to treat hypothyroidism.

If you miss a dose of a liothyronine or NDT drug, you can take your medication if you remember within a few hours. Dr. Morris does not, however, recommend taking a double dose if it’s been a full day since you missed your dose.

Doubling up is a bit more problematic because the pharmacology of T3 is very different than that of T4. The blood levels of T3 go up and down more quickly and dramatically after ingesting tablets. Thus, ingesting a double dose will exacerbate this and could, if done frequently, lead to some unfavorable symptoms in some individuals. If a patient missed a dose of a T3 medication, it is not advisable to “catch up” by taking a double dose.

The unfavorable symptoms Dr. Morris is talking include a rapid heart rate, heart palpitations, or nervousness, among others.

Antithyroid drugs — There are two types of antithyroid drugs used to treat hyperthyroidism. Methimazole — known by its brand name Tapazole — is the most commonly prescribed antithyroid drug. Propylthiouracil — a generic drug often known by its abbreviation PTU — is less commonly prescribed.

According to Dr. Morris, methimazole does not require taking it at precisely the same time daily. Doubling your dose a full day after missing a pill, however, is not recommended. Dr. Morris says:

If you forget to take your methimazole at your usual time in the morning, it’s safe to take it that same day in the afternoon or evening. Methimazole has a long half-life, but we don’t generally recommend doubling up after missing doses because of the risk of side effects. Patients should just resume taking the usual dose.

The guidelines are different for PTU. Dr. Morris says:

PTU generally requires divided dosing because of its short half-life. Thus, missing a dose here is just a missed dose. Patients shouldn’t “catch up” or take it later in the day unless they are taking PTU only once per day already.

Thyroid cancer patients — Remembering to take your thyroid medication is important for all thyroid patients, but missing doses is a particular concern for thyroid cancer patients on suppressive therapy. Patients on suppressive therapy receive a carefully calculated dosage of thyroid hormone replacement medication to keep TSH levels low — a proven way to help prevent recurrence of thyroid cancer.

According to Dr. Morris, if a patient on suppressive therapy to prevent thyroid cancer recurrence regularly forgets to take his or her levothyroxine, it can pose a risk. Says Dr. Morris:

The key is how often does the patient forget. If the patient misses even one dose per week, that is 14 percent of their weekly dose, which again because of the long half-life, reduces their daily dose by roughly a similar amount. This can be enough to allow the TSH to creep upwards and fall outside their target range for suppression. If the TSH is not suppressed, it can conceivably have a stimulatory effect on any tumors they may have. This is why we advise patients to “catch up” if they are sure they missed a tablet and to be as diligent as possible to get in all their doses.

Source: Email interview with Dr. John Morris, July 24, 2018

If you have a question for our HealthCentral experts, please submit here.

You should know: The answer above provides general health information that is not intended to replace medical advice or treatment recommendations from a qualified healthcare professional.

About levothyroxine

Type of medicine Thyroid hormone
Used for Underactive thyroid gland (hypothyroidism)
Also called (UK) Eltroxin®
Also called (USA) Levoxyl®; Levo-T®; Synthroid®; Tirosint®; Unithroid®
Combination brand: Thyrolar® (levothyroxine with liothyronine)
Available as Tablets and oral liquid medicine

If you have an underactive thyroid gland, it means that your thyroid gland does not produce enough thyroid hormone. This is a condition known as hypothyroidism. Levothyroxine (which is also called levothyroxine sodium) restores the balance of thyroid hormone in your body. It is very similar to thyroxine, the hormone which your body produces naturally.

Before taking levothyroxine

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking levothyroxine it is important that your doctor knows:

  • If you are pregnant or breastfeeding. This is so your doctor can keep a check on your baby.
  • If you have a heart problem such as angina, or if you have high blood pressure (hypertension).
  • If you have ever been told your adrenal gland is unable to produce enough of the hormone cortisol, a condition called adrenal insufficiency.
  • If you have been told your thyroid is overactive (producing too much thyroxine).
  • If you have high levels of glucose (sugar) in your blood (diabetes mellitus)
  • If you have been told you have a problem regulating the levels of water in your body, a rare condition known as diabetes insipidus.
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
  • If you have ever had an allergic reaction to a medicine.

How to take levothyroxine

  • Before you start this treatment, read the manufacturer’s printed information leaflet from inside your pack. The manufacturer’s leaflet will give you more information about levothyroxine and a full list of the side-effects which you may experience from taking it.
  • Take levothyroxine exactly as your doctor tells you to. Your doctor will ask you to take one dose each day, preferably before your breakfast. The number of tablets you need to take for each dose will be adjusted to suit you.
  • There are three strengths of tablet (25 micrograms, 50 micrograms and 100 micrograms) and your dose may be a combination of different strength tablets.
  • As a guide, it is usual for adults to start by taking a daily dose of 50-100 micrograms, and for this to be increased gradually to a daily dose of 100-200 micrograms. Your doctor or pharmacist will tell you what dose is right for you.
  • If levothyroxine has been prescribed for a child, the doctor will tell you what dose to give. The dose for children depends upon their weight, age and what they are being treated for. Give levothyroxine to your child at least half an hour before they eat their first meal of the day.
  • Most people find that levothyroxine tablets are easily swallowed. If you do have swallowing difficulties, some brands of tablet can be added to a little water and allowed to disperse before swallowing. Ask your pharmacist to check if your brand of tablet will disperse in water. Alternatively, ask your doctor to prescribe the oral liquid medicine for you.
  • If you forget to take a dose, take it as soon as you remember if it is still within two or three hours of your usual time. If it is longer than this before you remember, skip the forgotten dose. Do not take two doses together to make up for a missed dose.

Getting the most from your treatment

  • Try to keep your regular appointments with your doctor so your progress can be monitored. You will need regular blood tests to check your thyroid levels, particularly in the early stages of your treatment.
  • If you buy any medicines, check with a pharmacist that they are safe to take with levothyroxine. Levothyroxine should not be taken at the same time as indigestion remedies or preparations containing calcium or iron (which are contained in some vitamin products). These types of medicines reduce the amount of levothyroxine absorbed by your body. Leave at least two hours between taking your dose of levothyroxine and any such preparation.
  • Calcium or iron found in the food you eat can also reduce the amount of levothyroxine absorbed by your body. Try to take your dose at least 30 minutes before your first meal of the day.
  • If you have diabetes you may need to check your blood glucose more frequently, as levothyroxine may affect the levels of sugar in your blood. Your doctor will be able to advise you about this.
  • If you are having an operation or dental treatment, tell the person carrying out the treatment that you are taking levothyroxine.
  • Treatment with levothyroxine is usually lifelong. Continue to take this medicine unless your doctor tells you to stop.

Can levothyroxine cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the ones associated with levothyroxine. You will find a full list in the manufacturer’s information leaflet supplied with your medicine. Experiencing side-effects may be an indication that your dose needs adjusting, so speak with your doctor if you experience any of the symptoms listed below.

Levothyroxine side-effects What can I do if I experience this?
Feeling sick (nausea) or being sick (vomiting) Stick to simple foods – avoid rich or spicy meals
Diarrhoea Drink plenty of water to replace lost fluids
Headache Drink plenty of water and ask your pharmacist to recommend a suitable painkiller. If the headache continues, speak with your doctor
A feeling that your heart is pounding (palpitations) or chest pain Let your doctor know about this as soon as possible
Feeling restless, feeling flushed, feeling hot, sweating, difficulty sleeping, loss of weight, muscle cramps, temporary loss of hair, itchy rash, menstrual changes Discuss these with your doctor

If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.

How to store levothyroxine

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

6 Thyroid Medication Mistakes You Don’t Want to Make

The time of day you take your thyroid meds, and how you store them, can make or break your thyroid disease management.

For about one in seven of the 10-12 million Americans with an underactive thyroid gland, conventional treatment with the synthetic thyroid hormone levothyroxine just isn’t enough.1 Sometimes, the cause is simple and easy to fix —you may need a dose adjustment, a change in when you take your thyroid medication or in where you store it, for example. For others, the reasons are more mysterious and controversial. For instance, some experts say some people with hypothyroidism may benefit from adding a second thyroid hormone called T3. If you continue to feel sick, tired, depressed or have symptoms like stubborn weight gain, don’t reach for an over-the-counter thyroid booster (there can be dangers; see #5). It’s worth talking with your doctor about the best solution for you. Here are five thyroid medication mistakes that you might be making:

#1. You expect to feel better instantly. Some people start feeling more energetic and alert within a week or two of starting thyroid hormone. But for others, it could take a month or two to feel better. And you may have to see your doctor several times for tests of your blood levels of thyroid stimulating hormone (TSH) and adjustments to your levothyroxine dose to get it just right. 2

#2. You take your meds at the wrong time. For best absorption into your bloodstream, levothyroxine should be taken on an empty stomach 30-60 minutes before breakfast, or three or more hours after dinner. Taking it with or too soon before or after a meal or snack could reduce absorption to 64%, from a high of 80% when you’re fasting, according to the American Thyroid Association (ATA).3 Just changing your timing could bring your thyroid levels back into a normal range.

In one older but often-cited Italian study4 of four people whose thyroid numbers were not in control despite taking thyroid hormone, researchers found that they all took their medication just 15-20 minutes before breakfast. Changing their routine, so they took thyroid hormone 60 minutes before their morning meal, improved their numbers within a month. Take it with water. In another Italian study, coffee interfered with absorption.5 And don’t take antacids or supplements containing calcium or iron with four hours of your levothyroxine.6 Iron can make levothyroxine less effective according to the National Institutes of Health Office of Dietary Supplements 7. Calcium can interfere with absorption.8

#3. You switched from a brand-name to generic levothyroxine. Switching from a brand-name to generic thyroid hormone, or vice-versa could affect your TSH levels – even if the dose is the same. 9 The US Food and Drug Administration requires that all levothyroxine preparations deliver 95-105% of the potency on the label. But, the ATA notes, even tiny variations could make a difference. That’s why the group’s guidelines recommend sticking with the drug type (generic or brand name) to keep your TSH levels steady. (Ask for it at every refill.) If you’ve made a switch and have concerns, have your doctor retest your TSH level, the ATA, the American Association of Clinical Endocrinologists, and The Endocrine Society have recommended in a joint statement. 10

#4. You store your levothyroxine tablets in the wrong place. Keep this drug in cool, dry, dark place, like in a cabinet or on a shelf in a closet away from high-humidity environments like your bathroom. Exposing pills to excess heat, light, and moisture can make thyroid medications less effective. In a recent Italian study, one in 20 people with hypothyroidism whose TSH levels stayed outside the normal range despite taking levothyroxine had been stashing their tablets in the wrong places—next to heaters, near the shower in the bathroom, or in clear containers on tables beside a window. When they started keeping them in a better spot—and took those pills— their symptoms were reduced. 11

#5. You think adding T3 will help. Stories about the purported wonders of “T3” for hypothyroid symptoms are all over the internet. Some endocrinologists recommend that people whose hypothyroidism symptoms persist despite normal TSH levels try adding synthetic triiodothyronine (T3) to their levothyroxine therapy. It could work, but research suggests it doesn’t help everyone.

T3 is the body’s active form of the thyroid hormone thyroxine. Enzymes in organs like the liver, brain, and heart convert thyroxine (T4) into T3 and the thyroid gland produces some as well. For most people with hypothyroidism, the body converts levothyroxine into sufficient T3. But there’s evidence this doesn’t always happen. For about 15% of people with treated hypothyroidism whose TSH levels are in the normal range, T3 is still low, experts note.12 Taking a combination of T3 plus T4 can raise T3 levels… but that doesn’t always relieve lingering hypothyroidism symptoms, according to a recent review of 11 combo-therapy studies involving 1,216 people with hypothyroidism. Problems like tiredness, body aches, depression and weight gain did not improve significantly. 13 A 2016 Brazilian study of 32 people with hypothyroidism found that adding T3 didn’t improve their clinical symptoms any more than taking T4 alone. 14 And yet, combining T3 and T4 does seem to help some people – even when it doesn’t seem to raise their T3 levels. In one new study, published in April 2017 in the European Thyroid Journal, researchers found that combination therapy helped 24 out of 37 people in this situation – but it didn’t seem to matter whether they had low T3 levels beforehand or if their levels rose during treatment. 15

What’s going on? One clue is emerging. Early research from Chicago’s Rush University suggests that a genetic mutation could be responsible for lingering symptoms despite healthy TSH levels —by preventing enzymes from converting T4 into T3 in the body. But more studies are needed. 16

What should you do? If you’re curious about T3, talk it over with your doctor. It’s also wise to check that your health insurance covers testing and treatment. The ATA’s 2012 guidelines say L3-L4 combo therapy shouldn’t be used routinely because long-term studies have yet to prove it has benefits. But major groups outside the U.S., like the European Thyroid Association (ETA), say doctors there should consider it an “experimental treatment modality” for people whose fatigue, depression, weight gain and other hypothyroidism symptoms haven’t waned even though taking levothyroxine alone has moved their TSH levels into the normal range. 17

#6. You take “natural” thyroid medications and supplements. Many supplements claim to “support” thyroid health – but some are laced with thyroid hormones not listed on the label. Adding them to your medication could mean making a thyroid medication mistake of getting too much. In a 2013 study of 10 top-selling thyroid-support products sold on the internet, researchers from Germany’s Landstuhl Regional Medical Center and from the Walter Reed Army National Military Medical Center in Bethesda, MD, found that nine were laced with T3, T4 or both in a variety of amounts. Ingredient labels listed animal thyroid tissue for some while others only listed herbs such as ashwagandha, guggul, and Coleus forskohlii. The researchers concluded that drugs were added to the supplements.18 Supplements, including types containing a seaweed called kelp, may also contain dangerously high levels of iodine. Some experts also warn about an extremely rare threat that doesn’t seem to have ever actually happened, but could. Natural thyroid supplements may contain gland tissue from the thyroid, liver, heart, pancreas and other animal organs of cows—raising a tiny but serious risk for exposure to prions— agents that could transmit the brain disease Creutzfeldt–Jakob.19

Updated on: 10/10/17 Continue Reading 5 Surprising Facts about “Low Thyroid” in Children and Teens View Sources

1. “Guidelines for the Treatment of Hypothyroidism.” Jonklas J et al. THYROID.

Volume 24, Number 12, 2014. URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4267409/

2. https://www.endocrineweb.com/conditions/thyroid/hypothyroidism-too-little-thyroid-hormone-0

3. “Guidelines for the Treatment of Hypothyroidism.” Jonklas J et al. THYROID.

Volume 24, Number 12, 2014. URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4267409/

9. “Guidelines for the Treatment of Hypothyroidism.” Jonklas J et al. THYROID.

Volume 24, Number 12, 2014. URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4267409/

10. AACE, TES, and ATA: Joint Position Statement on the Use and Interchangeability of

Thyroxine Products. American Association of Clinical Endocrinologists, The Endorine Society and the American Thyroid Association.

13. “Thyroxine-triiodothyronine combination therapy versus thyroxine monotherapy for clinical hypothyroidism:

15. “Neither Baseline nor Changes in Serum Triiodothyronine during Levothyroxine/Liothyronine Combination Therapy Predict a Positive Response to This Treatment Modality in Hypothyroid Patients with Persistent Symptoms.” Medici BB et al. Eur Thyroid J. 2017 Apr;6(2):89-93. URL: https://www.karger.com/Article/FullText/454878

16. “Prevalent polymorphism in thyroid hormone-activating enzyme leaves a genetic fingerprint that underlies associated clinical syndromes.” EA McAnnich et al. J Clin Endocrinol Metab. 2015 Mar;100(3):920-33


Generic Name: levothyroxine (LEE voe thye ROX een)
Brand Names: Levoxyl, Synthroid, Tirosint, Unithroid

Medically reviewed by Sanjai Sinha, MD Last updated on Sep 2, 2019.

  • Overview
  • Side Effects
  • Dosage
  • Professional
  • Tips
  • Interactions
  • More

What is levothyroxine?

Levothyroxine is a thyroid medicine that replaces a hormone normally produced by your thyroid gland to regulate the body’s energy and metabolism.

Levothyroxine is given when your thyroid does not produce enough of this hormone on its own.

Levothyroxine is used to treat hypothyroidism (low thyroid hormone). It is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.

There are many brands and forms of levothyroxine available. Not all brands are listed on this leaflet.

Important Information

You may not be able to take levothyroxine if you have certain medical conditions. Tell your doctor if you have an untreated or uncontrolled adrenal gland disorder, a thyroid disorder called thyrotoxicosis, or if you have any recent or current symptoms of a heart attack.

Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of this medicine, especially if you are taking any other weight-loss medications or appetite suppressants.

Before taking this medicine

Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of this medicine, especially if you are taking any other weight-loss medications or appetite suppressants.

Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine. However, you may not be able to take this medicine if you have certain medical conditions. Tell your doctor if you have:

  • an untreated or uncontrolled adrenal gland disorder;

  • a thyroid disorder called thyrotoxicosis; or

  • symptoms of a heart attack (chest pain or heavy feeling, pain spreading to the jaw or shoulder, nausea, sweating, general ill feeling).

Tell your doctor if you have ever had:

  • a thyroid nodule;

  • heart disease, a blood clot, or a blood-clotting disorder;

  • diabetes (insulin or oral diabetes medication doses may need to be changed when you start taking this medicine);

  • kidney disease;

  • anemia (lack of red blood cells);

  • osteoporosis, or low bone mineral density;

  • problems with your pituitary gland; or

  • any food or drug allergies.

Tell your doctor if you have recently received radiation therapy with iodine (such as I-131).

If you become pregnant while taking levothyroxine, do not stop taking the medicine without your doctor’s advice. Having low thyroid hormone levels during pregnancy could harm both mother and baby. Your dose needs may be different during pregnancy.

Tell your doctor if you are breast-feeding. Your dose needs may be different while you are nursing.

Do not give this medicine to a child without medical advice. Tirosint is not approved for use by anyone younger than 6 years old.

How should I take levothyroxine?

Take levothyroxine exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Levothyroxine oral is taken by mouth. Levothyroxine injection is given as an infusion into a vein. Levothyroxine is usually given by injection only if you are unable to take the medicine by mouth.

Levothyroxine oral works best if you take it on an empty stomach, at least 30 to 60 minutes before breakfast. Follow your doctor’s dosing instructions and try to take the medicine at the same time each day.

Swallow the tablet>/b> or capsule whole, with a full glass (8 ounces) of water. The tablet may dissolve very quickly and could swell in your throat.

Measure liquid medicine carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

Levothyroxine doses are based on weight in children. Your child’s dose needs may change if the child gains or loses weight.

It may take several weeks before your body starts to respond to levothyroxine. Keep using this medicine even if you feel well. You may need to use this medicine for the rest of your life.

You may need frequent medical tests. Tell any doctor, dentist, or surgeon who treats you that you are using this medicine.

Store at room temperature away from moisture and heat.

Do not share this medicine with another person, even if they have the same symptoms you have.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include headache, leg cramps, tremors, feeling nervous or irritable, chest pain, shortness of breath, and fast or pounding heartbeats.

What should I avoid while taking levothyroxine?

Avoid the following food products, which can make your body absorb less levothyroxine: grapefruit juice, infant soy formula, soybean flour, cotton seed meal, walnuts, and high-fiber foods.

Levothyroxine side effects

Get emergency medical help if you have signs of an allergic reaction to levothyroxine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • fast or irregular heartbeats;

  • chest pain, shortness of breath;

  • fever, hot flashes, sweating;

  • tremors, or if you feel unusually cold;

  • weakness, tiredness, sleep problems (insomnia);

  • memory problems, feeling depressed or irritable;

  • headache, leg cramps, muscle aches;

  • feeling nervous or irritable;

  • dryness of your skin or hair, and/or hair loss;

  • changes in your menstrual periods; or

  • vomiting, diarrhea, appetite changes, weight changes.

Certain side effects may be more likely in older adults.

Common levothyroxine side effects may include:

  • muscle weakness;

  • headache, leg cramps;

  • nervousness, trouble sleeping;

  • diarrhea; or

  • skin rash, partial hair loss.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect levothyroxine?

Many other medicines can be affected by your thyroid hormone levels. Certain other medicines may also increase or decrease the effects of levothyroxine.

Certain medicines can make levothyroxine less effective if taken at the same time. If you use any of the following drugs, avoid taking them within 4 hours before or 4 hours after you take this medicine:

  • calcium carbonate (Alka-Mints, Caltrate, Os-Cal, Oyster Shell Calcium, Rolaids Soft Chew, Tums, and others);

  • cholestyramine, colesevelam, colestipol;

  • ferrous sulfate iron supplement;

  • sucralfate;

  • sodium polystyrene sulfonate (Kalexate, Kayexalate, Kionex);

  • stomach acid reducers–esomeprazole, lansoprazole, omeprazole, rabeprazole, Nexium, Prilosec, Prevacid, Protonix, Zegerid, and others; or

  • antacids that contain aluminum or magnesium–Gaviscon, Maalox, Milk of Magnesia, Mintox, Mylanta, Pepcid Complete, and others.

Many drugs can interact with levothyroxine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Levoxyl only for the indication prescribed.

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

Copyright 1996-2020 Cerner Multum, Inc. Version: 13.04.

Related questions

  • Effect of not taking medicine after thyroid removal?

Medical Disclaimer

More about levothyroxine

  • Side Effects
  • During Pregnancy or Breastfeeding
  • Dosage Information
  • Patient Tips
  • Drug Images
  • Drug Interactions
  • Compare Alternatives
  • Support Group
  • Pricing & Coupons
  • En Español
  • 555 Reviews
  • Drug class: thyroid drugs

Consumer resources

  • Levothyroxine Capsules
  • Levothyroxine Injection Solution
  • Levothyroxine Tablets
  • Levothyroxine Oral Solution
  • Levothyroxine (Advanced Reading)
  • Levothyroxine Injection (Advanced Reading)

Other brands: Synthroid, Levoxyl, Tirosint, Euthyrox, … +3 more

Professional resources

  • Levothyroxine Sodium (AHFS Monograph)
  • … +3 more

Related treatment guides

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



This case is an example of how hypothyroidism can manifest initially with nonspecific symptoms such as weakness, fatigue, and loss of interest and can progress to neurocognitive changes such as inattentiveness, inability to concentrate, slowing of thought processes, inability to understand complex tasks, and memory impairment.11

When Mr A’s mother died, he lost his sole source of adult support and guidance. There is no record of any inquiry as to the adequacy of his social supports, living situation, or income after his mother’s death. No referrals to the child protective agency were noted. Mr A was turned loose to fend for himself.

Providing appropriate social services at that time might have prevented Mr A’s subsequent first hospitalization and improved his quality of life. Even after the first hospitalization, no steps were taken to assure continuity of care even though the patient needed 3 months in a nursing home to recover functioning. The fact that Mr A developed serious psychiatric symptoms secondary to medication noncompliance resulting in the first hospitalization should have served as a “red flag” that special aftercare arrangements might be needed on a long-term basis.

However, in this patient, careful case management might not have been enough. An exploration of what his illness meant to him in terms of his future (it had killed his mother) might have highlighted fears or misconceptions that could have been addressed by the primary care physician or a counselor, resulting in improved compliance. Mr A eventually slipped into another pattern of noncompliance that resulted in the second hospitalization and the development of cognitive symptoms that were apparent on admission. If Mr A had not been brought in to receive treatment, he may have progressed into myxedema coma. Even after thyroid replacement therapy, Mr A continued to have residual neurocognitive impairment that led to what may be a permanent placement in a nursing home.

Medication noncompliance is common in adolescents. It can stem from many sources including a desire to not be different from peers, a belief of personal invulnerability, or a rebellion against authority figures who are seen as being overcontrolling.12 Since the discontinuation of treatment in hypothyroidism can lead to a return of symptoms in a short period of time,13 assuring close follow-up for adolescents should be the central feature of any management plan.

Providing the patient with education about medication is not enough. In a randomized controlled trial of thyroxine adherence, distributing booklets about thyroxine medication did not improve adherence between the study group and the control group.14 The doctor-patient relationship plays a key role in adherence to medication regimens. Physicians who use understandable language and encourage open doctor- patient exchanges in friendly, caring environments are more likely to foster participation by patients in their own medical care, increasing the likelihood of adherence. Asking simple questions regarding any difficulties in taking medication and the presence of side effects while addressing forgetfulness in a nonjudgmental manner will enhance the therapeutic relationship.15,16

Crowley, in his 14-year study on psychosis in myxedema,17 emphasized that only some patients responded to treatment. He recognized that some reasons for not responding to thyroid treatment might include not only noncompliance secondary to emotional and personality characteristics but also might even be due to the presence of neurocognitive damage that has not been fully realized by the clinician.

There are case reports that suggest that weekly direct observed thyroxine therapy can be effective in preventing relapse in noncompliant patients; however, more research is needed to confirm the efficacy of this approach in postsurgical thyroidectomy patients. The case reports suggest that a weekly total dose of levothyroxine (intramuscularly, intravenously, or orally) can work as effectively as daily doses and help to avoid noncompliance.18,19 All of these routes administered under direct observation either at a physician’s office or by a home health nurse showed benefit in moderate to severe cases of hypothyroidism in noncompliant patients.20 The rationale behind this treatment strategy is the long half-life of levothyroxine, which is in the range of 5.3 to 9.5 days.21–23 There may have been a better chance for compliance in this case if the patient had participated in a weekly dosing regimen.

In general medicine, the concept of disease management programs for chronic illnesses is becoming increasingly more common. Many of these programs have outreach to patients in the community, just as in the field of mental health, assertive treatment teams24 regularly go into the community to help patients deal with social, financial, and personal issues that impact compliance. Perhaps this proactive approach will become a standard of care for chronic medical illnesses as it is for chronic psychiatric illnesses.

Generic levothyroxine and brand-name Synthroid are two of the most commonly prescribed medications in the U.S. for the treatment of hypothyroidism. Other similar medications include Levoxyl, Tirosint, and Unithroid.

Synthetic thyroxine, the active ingredient in Synthroid and levothyroxine, is a prohormone, which means that it needs to get processed in our bodies to be converted to the active thyroid hormone. Once you start taking thyroid replacement, your healthcare provider will monitor your thyroid stimulating hormone (TSH) levels with blood tests and make adjustments to your dosage, as needed.

For those of you who have been taking thyroid hormone for a while, what could happen to mess up how well your medication is working? Here are eight common scenarios.

1) You switched between Synthroid and levothyroxine.

Because there may be subtle differences in how your body absorbs and processes the different thyroid medications, it is preferable to stay with one formulation when possible. The American Thyroid Association and The Endocrine Society recommend that you stick to brand-name Synthroid if that’s what your provider first prescribed to you. If you started with generic levothyroxine, you’ll not only want to keep taking the generic, but the generic made by the same manufacturer — your pharmacist can help you with that.

2) Your weight has changed quite a bit.

As with most medications, if you’ve gained or lost weight, you may need to adjust the dosage of your thyroid medication. Your provider will calculate how much to add or take away based on your weight change, and monitor how well you do with the new dosage. Though not a one-size-fits all recommendation, the average dose in adults is about 1.6 mcg/kg per day, which equates to 112 mcg once a day for a 70 kg adult.

3) You took it with food.

This is important: Synthroid and levothyroxine must 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.

Don’t miss out on savings! Get the best ways to save on your prescriptions delivered to your inbox. By signing up, I agree to GoodRx’s terms of service and privacy policy.

4) You took it with your vitamin supplements.

Iron and calcium supplements interfere with how your body absorbs your thyroid medications, so these should be spaced at least an hour apart.

Another supplement to watch out for is biotin, commonly taken for hair, skin, and nail benefits. Biotin doesn’t interfere with your thyroid medication, but it does interfere with your thyroid blood test and can mess up your numbers. Stop taking biotin at least 2 days before having a TSH blood test done.

5) You took it with your stomach medications.

Omeprazole (Prilosec), esomeprazole (Nexium), and pantoprazole (Protonix) belong to a class of medications known as proton pump inhibitors that can interfere with how you absorb your thyroid medications. If you take these medications at the same time, your provider may need to increase the dosage of your thyroid medication to compensate.

6) You started estrogen hormone replacement therapy.

A TSH blood test should be done 12 weeks after starting estrogen therapy to check your thyroid hormone levels. Estrogen, which is available as a pill, injection, or different skin preparations (like a cream, gel, or patch), can affect your thyroid medication. Women taking estrogen therapy may need more Synthroid or levothyroxine.

7) You eat a lot of fiber.

A high-fiber diet is a good thing! But if you’ve recently changed your diet and added more high-fiber foods, know that they can interfere with your body’s absorption of your thyroid medications. Talk to your provider about how to manage this. It could mean spacing out when you eat and when you take your medications. Examples of popular high-fiber foods include:

  • Vegetables
  • Fruits
  • Beans
  • Lentils
  • Nuts
  • Quinoa

8) You take your Synthroid or levothyroxine with coffee.

Even sips of coffee can affect your thyroid medication if the two aren’t spaced apart enough. In studies, coffee reduced the body’s absorption of thyroid medications by about 30%. That’s why experts recommend that you wait at least 60 minutes after drinking coffee to take your thyroid replacement medication. After taking your thyroid med, you should also wait at least an hour before drinking coffee.

– – –

Hope this helps.

Dr. O

Put drug prices & coupons in your pocket! We’ll text you a link to download our free Android or iPhone app Get GoodRx Mobile App Your link is on the way!

We’ve sent a link to download the GoodRx mobile app to your phone.

Something went wrong

We were unable to send a link to your phone.

About the author

Leave a Reply

Your email address will not be published. Required fields are marked *