Whats a water pill

Which diuretics are safe and effective for patients with a sulfa allergy?


Diuretics that do not contain a sulfonamide group (eg, amiloride hydrochloride, eplerenone, ethacrynic acid, spironolactone, and triamterene) are safe for patients with an allergy to sulfa. The evidence is contradictory as to whether a history of allergy to sulfonamide antibiotics increases the risk of subsequent allergic reactions to commonly used sulfonamide-containing diuretics (eg, carbonic anhydrase inhibitors, loop diuretics, and thiazides) (strength of recommendation: C, based on case series and poor quality case-control and cohort studies).

Clinical commentary

Are all sulfa drugs created equal?
Brian Crownover, MD, FAAFP
96 MDG Family Medicine Residency, Eglin Air Force Base, Fla

Historical bromides commonly fall by the wayside as better evidence becomes available. Who would have thought 15 years ago that we would be promoting beta-blockers for patients with congestive heart failure?

Likewise, with closer inspection, we have learned that not all sulfa drugs are created equal. The stereospecificity due to the absence of aromatic amines in common diuretics means they are safe for patients with known sulfa antibiotic allergies. Given that diuretics are older agents and off-patent, with no company to take up their cause, no one has been willing to challenge outdated package insert warnings.

As clinicians who regularly work without a net, we are accustomed to prescribing medications in less than ideal circumstances. Thankfully, reasonable evidence is available to support what many of us are already doing—using cheap thiazides for patients despite a history of sulfa allergy.

Evidence summary

Little research has been performed on sulfonamide antibiotic and sulfonamide diuretic allergic cross-reactivity. What we do know is that there are 2 classes of sulfonamides—those with an aromatic amine (the antimicrobial sulfonamides) and those without (eg, the diuretics acetazolamide, furosemide, hydrochlorothiazide, and indapamide). Hypersensitivity reactions occur when the aromatic amine group is oxidized into hydroxylamine metabolites by the liver. Sulfonamides that do not contain this aromatic amine group undergo different metabolic pathways, suggesting that allergic reactions that do occur in this group are not due to cross-reactivity in sulfa-allergic patients. But that point is far from settled by the research.

On one side, a large cohort study shows some cross-reactivity

A large retrospective cohort study using Britain’s General Practice Research Database identified 20,226 patients seen from 1987 through March 1999 who were prescribed a systemic sulfonamide antibiotic, and then at least 60 days later received a nonantibiotic sulfonamide (eg, thiazide diuretic, furosemide, oral hypoglycemic).1 Researchers reviewed records to determine whether patients described as having an allergic reaction to a sulfonamide antibiotic were at increased risk of having a subsequent allergic reaction to a sulfonamide nonantibiotic.

Patients were identified as being allergic using both narrow definitions (anaphylaxis, bronchospasm, urticaria, laryngospasm, or angioedema) and broad ones. As only 18 patients out of the 20,226 patients were reported as having an allergic reaction using the narrow definition, analysis was based on the broad definition. Added to the broad category were asthma, eczema, and other “adverse” drug effects that were not specified by the author.

Using this broad definition, researchers identified allergies to sulfonamide antibiotics in 969 patients. Of this group, 96 patients (9.9%) had a subsequent reaction to a sulfonamide nonantibiotic, which included drugs from the loop and thiazide diuretic classes (including bumetanide, chlorothiazide, furosemide, hydrochlorothiazide, indapamide, and torsemide). It was unclear if any patients taking a carbonic anhydrase inhibitor experienced an allergic reaction. For comparison purposes, of the 19,257 patients who were not identified as having an allergy to a sulfonamide antibiotic, again using the broad definition, 315 (1.6%), had a subsequent allergic reaction to a sulfonamide nonantibiotic, for an unadjusted odds ratio of 6.6 (95% confidence interval , 5.2–8.4).

When the results were adjusted for age, sex, history of asthma, use of medications for asthma or corticosteroids, the adjusted odds ratio for individuals experiencing an allergy to a nonantibiotic sulfonamide in those persons with a history of allergy to a sulfonamide antibiotic was 2.8 (95 % CI, 2.1–3.7). Of note, the adjusted odds ratio for the occurrence of a penicillin allergy in a patient with a history of sulfonamide antibiotic allergy was significantly higher at 3.9 (95% CI, 3.5–4.3).

Some limitations of the study included uncertainty of cause and effect of prescribed medications and subsequent reactions, possible inconsistency of physician diagnosis and coding, and lack of precision in the diagnosis of allergic reactions. There is also the possibility of “suspicion bias,” where patients with a history of allergies may be more closely monitored for subsequent reactions than nonallergic patients.


Main message

Sulfonamides are commonly used in primary care. Although trimethoprim-sulfamethoxazole and other sulfa-antibiotic combinations are especially widely used (sulfonamides were the first antibiotics ever introduced in 1936), this class of medication also includes many nonantibiotic agents. Table 1 lists the most common drugs containing a sulfa (SO2NH2) moiety in Canada. Several of these drugs are rarely thought of as sulfonamides.

Table 1

Commonly used sulfonamide nonantibiotic medications available in Canada

Adverse reactions to sulfa antibiotics are relatively common compared with such reactions to other antimicrobial agents. Adverse reactions have been estimated to occur in 3% of courses,1 but only 3% of these actually are true hypersensitivity.2 Unfortunately, hypersensitivity reactions to sulfonamides can be severe and even life-threatening. They include immediate, immunoglobulin E–mediated anaphylactic reactions and florid dermatologic reactions, such as Stevens-Johnson syndrome. Hypersensitivity reactions are more commonly characterized by fever or a maculopapular rash that develops 7 to 14 days after initiating the offending agent.2 There is no reliable skin test to rule out or confirm sulfa allergy.

There are important chemical differences between sulfa antibiotics and nonantibiotics. Most authors agree that nonantibiotics are less likely to cause severe reactions, and that the chemical differences between sulfa antibiotics and nonantibiotics make true cross-reactivity extremely unlikely.1-3 There is only one case report in the literature of anaphylaxis caused by furosemide4; the authors were unable to prove conclusively that the allergen was in fact chemically related to the sulfa moiety.5

Perhaps the most reassuring evidence comes from Strom et al,1 who elegantly turned the United Kingdom General Practice Research Database into a retrospective cohort study (level II evidence) to show that giving sulfa nonantibiotics to patients with a history of sulfa (antibiotic) allergy carries little risk of cross-reactivity. The authors reviewed the charts of 969 patients who had had allergic reactions to sulfonamide antibiotics and of 19 257 patients who had not. All these patients subsequently received sulfonamide nonantibiotics. For this study, “allergy” was defined very broadly and included development of eczema and various unspecified adverse effects within a full month of receiving the medication in question, making underreporting bias unlikely. Although Strom and colleagues found that patients allergic to sulfonamide antibiotics were more likely than nonallergic patients to react to sulfonamide nonantibiotics (9.9% vs 1.1%), they also found that the rate of reaction was even greater among patients allergic to penicillin who received sulfonamide nonantibiotics (14.2%). Penicillins do not have a sulfonamide moiety, so the researchers argued that any sulfonamide cross-reactivity appears predominantly related to a greater predisposition to allergic reactions in general among patients allergic to sulfonamide antibiotics, rather than to a specific sulfa hypersensitivity.

In our case, our patient’s previous reactions to “sulfa” drugs and hydrochlorothiazide were not well documented, and neither she nor the pharmacist could recall the specific nature of the reactions. Since the patient thought that her reactions were serious, and because her allergy extended to both antibiotic and nonantibiotic sulfonamides, I was compelled to find an alternative to furosemide.

A look at Table 1 shows that most diuretic agents are sulfonamide derivatives. The only diuretics that are not are the potassium-sparing diuretics (triamterene, spironolactone, and amiloride) and ethacrynic acid.6 At the time, the pharmacist informed me that they did not have any ethacrynic acid in stock, so I chose amiloride. I realized that it did not have the same natriuretic effect as ethacrynic acid, the agent of choice in this case, and that she needed close follow-up as she was also taking an angiotensin-converting enzyme inhibitor. Some might argue that spironolactone, a potassium-sparing agent with strong anti-aldosterone activity, would be preferable based on the landmark Randomized Aldactone Evaluation Study7 that showed improved survival among patients with severe (class III or IV) congestive heart failure using it. My patient, however, did not have this degree of illness. Several weeks after starting amiloride (10 mg by mouth daily), Mrs MacDonald developed hyperkalemia (K+ = 6.3 mmol/L). By this time, however, the pharmacy had received ethacrynic acid tablets, and my patient is now doing well on this medication at a dose of 50 mg daily and is no longer complaining of dyspnea or edema.

Yes, but…

Frusemide, like other non-antibiotic sulfa drugs lack the specific moieties present in antibiotic sulfa drugs (sulphonamides) that are thought to mediate hypersensitivity. These moieties are:

  • the N1 heterocyclic ring — causes type I hypersensitivity reactions.
  • the N4 amino nitrogen — results in reactive metabolites that cause either direct cytotoxicity or an immunologic response.

The best evidence available concerning sulfa drug cross-reactivity is probably Strom et al’s (2003) retrospective cohort study. These investigators studied 969 patients who had allergic reactions to sulfonamide antibiotics, and 19257 patients who had not, who subsequently received sulfonamide nonantibiotics. Using a very broad definition of ‘allergy’ patients allergic to sulfonamide antibiotics were more likely than nonallergic patients to react to sulfonamide nonantibiotics (9.9% vs 1.1%). However, there was an even higher rate among patients with documented penicillin allergy (14.2%)! Thus it is more likely that a reaction is related to a greater predisposition to allergic reactions in general among these patients rather than any specific sulfa hypersensitivity.

Expert opinion suggests that cross-reactivity between antibiotic sulfa drugs and non-antbiotic sulfa drugs is extremely unlikely.

Incidentally, there has only been one reported case of anaphylaxis to frusemide, and it could not be determined if the sulfa moiety was responsible.

Ponka (2006) summarises the approach to the problem of non-antibiotic sulfa drugs in patients with ‘sulfa drug allergy’ a bit like this:

  • Is there a history of severe or life-threatening sulfa allergy?
    YES —> do NOT give a non-antibiotic sulfa drug except in an emergency and there are no available alternatives.
    NO —> ask the next question…
  • Is there a history of allergy to non-antibiotic sulfa drugs?
    YES —> do NOT give a non-antibiotic sulfa drug except in an emergency and there are no available alternatives.
    NO —> give a ‘test dose’ in a monitored setting after appropriate patient counseling, or use an available alternative.

Always seek the opinion of an allergist/ immunologist first.

Some additional comments:

Ponka’s approach is cautious. From what we know of the pharmacology mediating antibiotic sulfa drug hypersensitivity and the limited evidence available, there is no reason to suspect that there should be cross-reactivity with non-antibiotic sulfa drugs. However, absence of evidence is not the same as evidence of absence…

I am not aware of any established protocols describing how to give a ‘test dose’ in this situation. I suspect that the risk is sufficiently low (when there is no history of a severe sulfa drug reaction, and no history of a reaction to a non-antibiotic sulfa drug) that the usual treatment dose could be given followed by a period of close observation. A more cautious approach (as suggested by Daman Langguth, see comments below) would be to give 1/10th of the usual dose.

Finally, it is rare that a sulfa drug ever needs to be given as a true emergency.

Tips for taking diuretic medications

Often called water pills, these drugs help lower blood pressure and are a mainstay for treating heart failure.

Updated: September 25, 2019Published: January, 2017

Diuretics, commonly called “water pills,” are the oldest and some of the least expensive class of drugs used to treat high blood pressure. They help the kidneys eliminate sodium and water from the body. This process decreases blood volume, so the heart has less to pump with each beat, which in turn lowers blood pressure. People with heart failure, who often gain weight because their bodies hold onto excess fluid (a condition called edema), are often prescribed diuretic medications.

Not surprisingly, one of the most common side effects of taking water pills is frequent urination. Other possible side effects include lightheadedness, fatigue, bowel changes, and muscle cramps. Men may occasionally experience erectile dysfunction.

In addition to getting rid of extra salt in your body, diuretic medications also affect levels of potassium. This mineral plays a key role in controlling blood pressure, as well as nerve and muscle function. In general, your kidneys help regulate potassium levels in your blood. But age, diabetes, heart failure, and certain other conditions may impair kidney function. And while some water pills tend to lower potassium levels, others have the opposite effect.

Thiazide diuretics, such as chlorothiazide (Diuril), chlorthalidone (Hygroton), and hydrochlorothiazide (Esidrix, HydroDiuril, Microzide) tend to deplete potassium levels. So do loop diuretics, such as bumetanide (Bumex) and furosemide (Lasix). If you take these medications, your doctor will likely encourage you to eat more potassium rich foods and beverages and limit salt intake.

Potassium-sparing diuretics, which include amiloride (Midamor), spironolactone (Aldactone), and eplerenone (Inspra), avoid the potential problem of potassium loss. But the opposite problem can occur. If potassium levels become too high, it can cause dangerous heart rhythm problems and even cardiac arrest.

People with high blood pressure or heart failure are often advised to limit how much salt or sodium they consume. One way to do that is to use salt substitutes, but these products are high in potassium—a quarter teaspoon of one brand contains about 800 mg of potassium. So, people who take potassium-sparing diuretics should avoid these products.

If you take any diuretic medication, ask your doctor whether you need periodic testing of your potassium and kidney function.

To learn more about managing hypertension, buy “Controlling Your Blood Pressure: What to do when your doctor says you have hypertension.”

– By Julie Corliss
Executive Editor, Harvard Heart Letter

As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

NHS Greater Glasgow and Clyde

E.g. Bendroflumethiazide, furosemide, and bumetanide.
What do Diuretics do?
How do I take them?
Side effects
What else should I know?

What do diuretics do?

Diuretics (water tablets) help to remove water and salt from your body. There are two types of diuretic; gentle, long-acting ones e.g. bendroflumethiazide (bendrofluazide) which are usually used to treat high blood pressure, and powerful short-acting ones e.g. furosemide (frusemide), bumetanide which are usually used for fluid retention.
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How do I take them?

  • You usually take gentle, long acting diuretics by mouth once each day in the morning. The effects of bendroflumethiazide (bendrofluazide) start within 1-2 hours of taking and can make you pass more urine for the first 14 days when taking it. For many people though the bendroflumethiazide (bendrofluazide) 2.5mg dose does not usually make them pass more water.
  • It is best to take the bendroflumethiazide (bendroflazide) each morning as it is easier to remember.
  • The powerful, short acting diuretics can be taken once or twice a day and at any time when it is most convenient. Furosemide (frusemide) and bumetanide will make you want to empty your bladder about half an hour after you take them. The effect will last for about 6 hours so if you are taking the tablets twice a day make sure you take the last dose in the afternoon at least 8 hours before going to bed.

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Side effects

Diuretics don’t usually cause any problems, however they can lower the amount of potassium in the body and your GP will check this with blood tests. It is important to continue to drink fluid normally (unless fluid intake is restricted by your doctor) as you can become dehydrated if you reduce your fluid or when the weather is hot. High doses of water tablets may worsen or occasionally cause gout. If you are affected please discuss this with your doctor or pharmacist.
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What else should I know?

A high salt (sodium chloride) intake can worsen fluid retention and counteract the beneficial effects of diuretic medication. Therefore you should reduce the amount of salt (sodium) in your diet and avoid adding salt to your food. Processed foods, e.g. canned foods and takeaways, contain very high levels of salt and you should avoid them if possible.

You should also always check with your pharmacist before you buy any medication as some items have a high sodium content e.g. effervescent (fizzy) tablets and remedies for heartburn and indigestion. You should avoid “Lo Salt” as it contains a lot of potassium which can cause problems in people with heart disease and with certain medicines.

If you think you have any side effects from this medicine be sure to mention them to you GP, practice nurse or pharmacist.
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Diuretics (also called water pills or fluid pills) are medicines that increase the amount of urine you produce. Urination is the body’s way of removing excess salt and water. Not only does this relieve symptoms such as ankle swelling, it also helps to lower blood pressure.

There are several different classes of diuretics, including carbonic anhydrase inhibitors, loop diuretics, potassium-sparing diuretics, and thiazide diuretics. Each type works in a distinct way and in different parts of the kidney cell (called a nephron).

What are diuretics used for?

Diuretics are used to treat conditions that have fluid retention (also called edema) as a symptom, such as heart failure, kidney failure and cirrhosis of the liver.

They are also effective at reducing blood pressure and some (such as thiazides and loop diuretics) are used in the treatment of high blood pressure (hypertension). Carbonic anhydrase inhibitors are mainly used in the treatment of glaucoma and are sometimes used off-label for altitude sickness.

What are the differences between diuretics?

Each class of diuretic works in a different way to remove salt and water from the kidney, which means they have different potencies and different side effects. Below, we have grouped the most common diuretics into their respective classes.

Thiazide diuretics

Thiazide diuretics inhibit the sodium/chloride cotransporter located in the distal convoluted tubule of a kidney cell. This decreases the amount of sodium reabsorbed back into the body, which results in more fluid being passed as urine. Thiazides are relatively weak diuretics.

Generic name Brand name examples
bendroflumethiazide Only available in the U.S. in combination with nadolol (Corzide)
chlorothiazide Diuril
chlorthalidone Thalitone
hydrochlorothiazide (HCTZ) Aquazide H, Microzide
indapamide Lozol
metolazone Mykrox, Zaroxolyn

Loop diuretics

Loop diuretics work by inhibiting the sodium-potassium-chloride (Na+/K+/2Cl) cotransporter in the thick ascending loop of Henle, a distinct area in the kidney cell. They are potent diuretics.

Generic name Brand name examples
ethacrynic acid Edecrin, Sodium Edecrin
bumetanide Bumex
furosemide Lasix
torsemide Demadex

Potassium-Sparing Diuretics

Potassium-sparing diuretics interfere with the sodium-potassium exchange in the distal convoluted tubule of a kidney cell. Some block the aldosterone receptor. Aldosterone is a hormone that promotes the retention of sodium and water. They are relatively weak diuretics; however, they do not cause hypokalemia (low potassium levels) but may cause hyperkalemia (high potassium levels), especially if they are used with other agents that also retain potassium, such as ACE inhibitors.

Generic name Brand name examples
amiloride Midamor
eplerenone Inspra
spironolactone Aldactone, CaroSpir
triamterene Dyrenium

Carbonic anhydrase inhibitors

Carbonic anhydrase inhibitors act by increasing the amount of bicarbonate, sodium, potassium, and water excreted from the kidney. They are relatively weak diuretics. They also reduce fluid levels in the eye and may be used to treat glaucoma and are sometimes used off-label to treat altitude sickness.

Generic name Brand name examples
acetazolamide Diamox

Are diuretics safe?

When taken at the recommended dosage, diuretics are considered safe. However, they have been associated with several serious adverse effects including:

  • Stevens-Johnson syndrome, erythema multiforme and other severe reactions in people with a sulphonamide allergy who have taken a sulphonamide-containing diuretic (includes acetazolamide, thiazides, or loop diuretics)
  • Severe neurological changes have occurred in people with liver disease given loop diuretics who are already electrolyte depleted
  • Tinnitus or hearing impairment have been reported with loop diuretics, mainly after intravenous administration, or in people with kidney disease, low protein levels, or administered another medicine that may also affect hearing
  • Excessive urination can occur which may cause dehydration with the potential for adverse cardiovascular events such as a stroke or blood clots.

What are the side effects of diuretics?

Side effects vary depending on the type of diuretic taken: however, the more common side effects of diuretics include:

  • Changes in electrolyte levels (such as potassium, sodium, calcium or magnesium levels), depending on the type of diuretic
  • Constipation
  • Dizziness
  • Dry mouth
  • Gout
  • A headache
  • An increase in blood sugar levels
  • Muscle cramps
  • Stomach upset
  • Tiredness.

For a complete list of side effects, please refer to the individual drug monographs.

What Is a Diuretic?

Also known as “water pills,” these drugs rid the body of extra water and lower blood pressure.

Diuretics are a class of medications commonly known as “water pills.”

They’re prescribed to treat high blood pressure; swelling of the feet, ankles, and lower legs and fluid in the lungs caused by heart failure; fluid buildup in the abdomen caused by liver damage or certain cancers; and eye conditions such as glaucoma.

Other conditions that may be treated with diuretics include diabetes insipidus, polycystic ovarian syndrome (PCOS), kidney stones, male-pattern baldness in women, and osteoporosis.

There are several different classes of diuretics, each of which works differently in the kidneys to help rid the body of extra water and salt.

Examples of diuretics include:

  • Loop diuretics, such as Lasix (furosemide), bumetanide, Demadex (torsemide), and Edecrin (ethacrynic acid)
  • Thiazide diuretics, like Microzide (hydrochlorothiazide), chlorthalidone, and Zaroxolyn (metolazone)
  • Potassium-sparing diuretics, including Aldactone (spironolactone), Inspra (eplerenone), Dyrenium (triamterene), and Midamor (amiloride)
  • Carbonic anhydrase inhibitors such as Diamox (acetazolamide) — mainly used for glaucoma and altitude sickness

Warnings and Precautions

Don’t take diuretics if you have trouble urinating, or if you’re allergic to the active or inactive ingredients found in the medication.

Ask your doctor if you should avoid or be cautious using diuretics if you:

  • Have severe liver or kidney disease
  • Are dehydrated
  • Have an irregular heartbeat
  • Are in the third trimester of pregnancy and/or have developed high blood pressure during your pregnancy
  • Are age 65 or older
  • Have gout
  • Are allergic to sulfa drugs, like Septra and Bactrim (sulfamethoxazole with trimethoprim)
  • Are already taking drugs that can damage hearing, like the cancer drugs Platinol (cisplatin) and carboplatin; salicylates like aspirin and Pepto-Bismol (bismuth subsalicylate); or aminoglycosides like amikacin and gentamin

Common Side Effects

It’s not uncommon to experience any of the following while taking a diuretic:

  • Dizziness or headache
  • Thirstiness
  • Rash or itching
  • Higher blood glucose or cholesterol level
  • Changes in your sexual function or menstrual period
  • Muscle cramps (loop diuretics)
  • Ringing in the ears (loop diuretics)
  • Low sodium, potassium, and/or magnesium levels in the blood (loop diuretics)
  • High potassium levels in the blood (potassium-sparing diuretics)
  • Enlarged breasts in men (Aldactone and Inspra)

Drug Interactions

Many drugs can interact with diuretics, but double-check with your doctor or pharmacist to make sure you’re not taking more than one diuretic at a time (unless your doctor has told you otherwise).

Don’t take loop diuretics if you’re taking Tikosyn (dofetilide).

Make sure your potassium is carefully monitored if you’re using digoxin and a loop or thiazide diuretic.

Dosages of insulin and oral diabetes medications may need to be adjusted while using diuretics.

Ask your doctor about diuretics if you’re taking the mood stabilizer Lithobid (lithium), or if you’re taking any medication that may lead you to feel dehydrated.

If you’re not taking a diuretic for high blood pressure, experts say you should ask your doctor about switching medications.

By Sid Kirchheimer
WebMD Feature

Reviewed By Charlotte Grayson

The largest hypertension study ever conducted has found that the simple “water pill” is preferred to newer, more popular and expensive drugs and should be the designated choice “for use in starting treatment for high blood pressure.”

But what if you’re among the 24 million Americans taking other types medications to manage hypertension? Should you talk to your doctor of switching to a diuretic (water pill), whose use has dwindled in recent decades with the introduction of newer drugs?

“Yes,” says the lead researcher of this landmark study, called ALLHAT for the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial.

“The bottom line of our study is that diuretics should be considered as the first step for treating all new cases of hypertension,” Barry R. Davis, MD, PhD, of the University of Texas School of Public Health, tells WebMD. “But diuretics should also be part of every hypertensive regimen.”

Davis adds that while the study findings recommend using diuretics to start treatment of high blood pressure, it shouldn’t be interpreted to suggest that only newly diagnosed patients would benefit from them.

“The way the clinical trail was conducted, 90% of the study participants had been on some type of medication , and their medication was stopped and they were switched to four different drugs in randomized fashion — including the diuretic,” he says. “And those taking the diuretics, which are much less expensive, fared as good or better.”

Plus, they don’t cause any additional side effects than the other drugs — typically increased urination that subsides after several weeks, and sometimes dizziness, muscle weakness, and cramps. “In rare cases, someone can’t take them because they may be allergic to them,” says Davis. “But for the average patient, they are the better choice. So if you are on another medication and your blood pressure is not controlled, and another medication has to be added, as is often the case, it should be a diuretic.”

The results of the eight-year ALLHAT trial, released recently in the Journal of the American Medical Association, brings new attention to this old standard in blood pressure treatment, which works by ridding the body of excess salt and water. The generic diuretic used in the study, chlorthalidone, was deemed a better choice than two other types of treatments that can cost as much as 30 times more — the ACE inhibitors Prinivil or Zestril and the calcium channel blocker Norvasc. A third medication, the alpha-blocker Cardura, was dropped from the study some two years ago because it increased the risk of heart disease and stroke in study participants.

The diuretic was found to be better at lowering systolic blood pressure — the top number in a blood pressure reading — than the newer drugs, but Norvasc was more effective in reducing diastolic blood pressure, the bottom number. However, those taking Norvasc had a 38% higher risk of developing heart failure and a 35% higher chance of being hospitalized for the condition. Meanwhile, those on the ACE inhibitor had a 15% higher risk of stroke, a 19% higher risk of developing heart failure, and other increased risks compared with people taking a diuretic.

And then there’s the cost factor: While diuretics cost between 6 cents and 10 cents a day, it costs about $1.60 daily for a beta-blocker (another drug used to treat high blood pressure) and $1.46 for an ACE inhibitor. There are various types of diuretics for hypertension management, but the most popular is hydrochlorothiazide, or HCTZ, which has fewer side effects than the type used in the ALLHAT study. HCTZ is often combined with other diuretics into one pill.

So why have diuretics dropped in popularity in recent years? In 1982, diuretics represented 56% of all prescriptions written for high blood pressure; ten years later, they comprised only 27% of those prescriptions.

“Physicians have changed their practice , based on the assumption that if it’s newer, it probably is better, says Paul K. Whelton, MD, MSc, of Tulane University School of Public Health and Tropical Medicine, another researcher on the study. “But the use of diuretics has certainly been the recommendation from every national body that has offered treatment guidelines.

“What this finding does is provide a definitive answer to the question of what medication is best,” Whelton tells WebMD. “Now, there is strong scientific evidence that there is clearly no additional benefit from newer agents that are more expensive. And when you look at evidence of important clinical indicators — namely heart failure and stroke, diuretics perform better.”

But switching from newer drugs to a diuretic, the study researchers say, would save between $250 and $650 per patient per year. So is the medical community bracing for a change in the way high blood medications are prescribed?

“This study will lead physicians to rethink how they treat high blood pressure,” says Daniel Jones, MD, of the American Heart Association, in a prepared statement. “But we strongly urge patients to continue taking their current medication until they have talked with their physician to determine the best treatment.”

Meanwhile, a spokesman for the American Medical Association says that the governing body of practicing physicians — which publishes the medical journal in which the study appeared — “has not yet reviewed the study and therefore cannot make a recommendation.”

Published Jan. 2, 2003.

SOURCES: The Journal of the American Medical Association, Dec. 18, 2002 • Barry R. Davis, MD, PhD, professor of biometry, University of Texas School of Public Health, Houston • Paul K. Whelton, MD, MSc, dean and professor of epidemiology, Tulane University School of Public Health and Tropical Medicine, New Orleans • American Heart Association statement, Findings of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) • American Medical Association, Chicago.

Maybe you ate way too much on your vacation last week. Maybe you haven’t been as *ahem* regular as you normally are. Maybe it’s just that time of the month. Whatever it is, you’re swollen and puffy and it’s super uncomfortable.

Sooo…should you just pop a few OTC water pills to help you ditch the bloat and feel normal again?

Hold on, what are water pills, anyway?

Water pills (a.k.a. diuretics) basically pressure your kidneys into flushing out excess water and salt through your pee.

There are actually three classes of diuretics that work in different ways, says Ellen Lunenfeld, M.D., an internist with Summit Medical Group in New Jersey—thiazide, loop-acting, and potassium-sparing diuretics. Each class works on a different part of the kidney’s nephron where urine is made, says Lunenfeld.

They sound pretty harmless, right? After all, you’re just peeing more.

Actually, it goes a little deeper than that. Here’s what you need to know about water pills—and why you should definitely skip self-prescribing them.

1. Water pills are one of the most commonly prescribed medications.

Take note of that word: prescribed. Water pills are meant to help reduce blood pressure, prevent fluid buildup, and reduce swelling respectively, says Linda Anegawa, M.D., an internist at Pali Momi Medical Center in Hawaii.

They’re usually given to people with health issues like hypertension, heart failure, and idiopathic edema (unexplained swelling)—not people looking to cure mild bloating or lose weight. Most doctors recommend against using water pills for those purposes.

2. OTC water pills are different from prescription water pills.

It might be tempting to pick up an OTC water pill at the drugstore if you’re experiencing mild bloating, but Lunenfeld warns against this. That’s because OTC water pills and prescriptions water pills aren’t the same thing.

“The problem with OTC meds like these is that you’re not sure exactly what they’re giving you,” she explains. “They’re not FDA controlled, so they may not be doing what they claim to and in fact might be making you dehydrated.” (With an Rx, a doctor will monitor your dosage and length of use—that doesn’t happen with OTC water pills, hence the dehydration risk.)

Going a step further, OTC water pills could even be toxic and interact badly with other medicines you’re taking, says Anegawa. (Again, with a prescription, a doctor will be monitoring this.) OTC water pills also haven’t been studied in research trials to prove their efficacy, she adds.

3. Water pills aren’t addictive, but they can be dangerous.

Water pills aren’t habit-forming or dangerous, says Anegawa—again, as long as you’re getting them through your doctor. When you start taking them on your own without a recommended dosage, however, you could do some serious damage to your body.

“ can cause worsening kidney function, and lightheadedness or dizziness as a result of being dehydrated,” says Lunenfeld. Other scary symptoms caused by dehydration and loss of electrolytes includes heart palpitations, weakness, confusion, and severe dizziness.

3. They don’t really help you lose weight…

Sure, water pills help you shed excess water that’s making you feel super bloated—but only temporarily. Once you stop taking them, your kidneys go back to reabsorbing the normal amount of water and salt for your body, so you’ll go back to your typical body weight soon after you stop taking them.

“When you’re weighing yourself, bone, fat, muscle and water,” says Lunenfeld. “When you’re looking to lose weight, you’re looking to lose fat and maintain muscle mass. With a diuretic, you’re just losing water weight, which isn’t really getting you any significant weight loss.”

4. In fact, they might make you gain weight.

Yep, you read that right. If you take any type of diuretic over a long period of time, your kidneys will eventually compensate for their use and you’ll end up holding on to more water weight than you did before you started taking them.

It’s called diuretic-induced edema, which happens when your kidneys start retaining more sodium and water than they need and your body starts to swell, says Anegawa—kind of the opposite of what a water pill is supposed to do.

5. Prescriptions water pills can be helpful if you’re on your period.

While it’s not recommended for healthy women to take any kind of water pills, there is one exception: to reduce period bloating. According to Anegawa, it’s fine for women to take prescription water pills to help de-puff unexplained leg swelling or bloating caused by PMS, says Anegawa.

Again, that’s prescription-only, so don’t head to your nearest drugstore for diuretics. Instead, bring up the issue to your ob-gyn, who may prescribe water pills to take before your period or whenever you tend to feel super-inflated. Since your physician will be keeping an eye on your dose, you’ll reduce your risk of serious side effects and have someone to call if something feels off.

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