Aldactone (Spironolactone): Uses, Side Effects, and Safety

Aldactone is the original brand name for spironolactone, a medication developed in the late 1950s that blocks the hormone aldosterone from telling your kidneys to hold onto sodium and water. That single mechanism turned out to have surprisingly wide-ranging consequences in the body, which is why the same pill prescribed for heart failure in one patient might be prescribed for acne or excess facial hair in another. The drug’s anti-androgen properties, discovered after it was already on the market, opened an entirely different chapter of uses that now rival its cardiovascular ones in everyday practice.

How Aldactone Works

Aldosterone is a hormone your adrenal glands produce to regulate sodium, potassium, and fluid balance. It acts on receptors in the kidneys, telling them to reabsorb sodium and excrete potassium. Spironolactone sits on those same receptors and blocks aldosterone from binding, so the kidneys let more sodium and water pass into the urine while retaining more potassium. This is why spironolactone is classified as a “potassium-sparing diuretic,” in contrast to common diuretics that flush potassium out along with the extra fluid.

But the drug does not stop at the kidney. Spironolactone also blocks androgen receptors throughout the body, interfering with the ability of testosterone and its potent derivative dihydrotestosterone (DHT) to exert their effects on tissues like skin, hair follicles, and the prostate. Research dating back to the 1970s showed that spironolactone competes with DHT for binding to its receptor, acting as a peripheral androgen antagonist without actually reducing the enzyme that converts testosterone into DHT.¹ This dual personality, part diuretic and part anti-androgen, explains the drug’s unusually long list of clinical uses.

Once swallowed, spironolactone is rapidly broken down by the liver into several active metabolites, the most studied being canrenone. Blood levels of the drug and its metabolites peak within about three hours, and while the parent compound disappears quickly, canrenone lingers with a half-life that stretches to roughly 17 hours in its slower elimination phase.² This extensive liver processing is one reason the drug interacts with a number of other medications, and why liver disease can change the way it behaves in your body.³

Heart Failure

The landmark trial that put spironolactone on the cardiology map was RALES (Randomized Aldactone Evaluation Study), published in 1999. It enrolled patients with severe heart failure and a left ventricular ejection fraction of 35% or less, all of whom were already on standard therapy including an ACE inhibitor and a loop diuretic.⁴ The trial found that adding a low dose of spironolactone substantially reduced the risk of death and hospitalization, and it was stopped early because withholding the drug from the placebo group was considered unethical.

Subsequent real-world studies have painted a more nuanced picture. A large observational analysis of heart failure patients with reduced ejection fraction found that aldosterone antagonist therapy did not significantly improve overall mortality or cardiovascular readmission rates after accounting for treatment selection, though heart failure readmission specifically was lower among treated patients at three years.⁵ This gap between the original trial results and real-world data is a familiar problem in cardiology: randomized trials carefully select patients and monitor them closely, while everyday practice involves older, sicker, and less carefully followed populations.

Resistant Hypertension

If your blood pressure stays elevated despite taking three or more medications at full dose (one of which should be a diuretic), you meet the definition of resistant hypertension. Spironolactone has become a go-to add-on for exactly this scenario. The PATHWAY-2 trial, a well-designed crossover study, compared spironolactone against two other add-on drugs (doxazosin and bisoprolol) and placebo in patients with resistant hypertension. Spironolactone lowered home systolic blood pressure by about 9 mmHg more than placebo and roughly 4 mmHg more than either competing drug.⁶ The advantage was especially pronounced in patients with low renin levels, which makes physiological sense because low renin often signals that excess aldosterone is driving the problem.

A systematic review and meta-analysis pooling data from multiple trials confirmed these findings, reporting that spironolactone reduced office systolic blood pressure by about 20 mmHg more than placebo and 24-hour ambulatory systolic blood pressure by about 7 mmHg more than alternative add-on drugs.⁷ An earlier non-randomized study of over 1,400 patients with blood pressure uncontrolled despite an average of three other medications saw a mean drop of about 22/10 mmHg with spironolactone, and this effect held regardless of age, sex, smoking, or diabetes status.⁸ For people stuck on multiple blood pressure pills with readings that refuse to budge, spironolactone is one of the most consistently effective options available.

Primary Aldosteronism

Sometimes the reason blood pressure won’t come down is that the adrenal glands are pumping out too much aldosterone on their own, a condition called primary aldosteronism (historically known as Conn’s syndrome when caused by an adrenal tumor). About two-thirds of cases stem from bilateral adrenal hyperplasia rather than a single tumor, and those patients generally cannot be cured surgically. For them, long-term aldosterone blockade with spironolactone is the standard medical treatment. Doses typically start low, around 25 to 50 mg daily, and often produce substantial blood pressure improvement.⁹ Spironolactone was actually one of the earliest treatments used after the first case of primary aldosteronism was described in 1955, and it remains the first-line medical therapy for the condition decades later.

Liver Cirrhosis and Ascites

People with advanced liver cirrhosis often develop ascites, the accumulation of fluid in the abdomen. The underlying mechanism involves a form of secondary aldosteronism: the failing liver triggers hormonal changes that cause the kidneys to hold onto sodium and water aggressively. Spironolactone directly counteracts this by blocking aldosterone’s action on the kidneys.¹⁰ It is a mainstay of ascites management, frequently paired with a loop diuretic to enhance fluid removal. The treatment provides symptomatic relief, helping drain excess fluid and making patients more comfortable, though it does not change the underlying course of the liver disease itself.

Acne in Women

Because spironolactone blocks androgens, it has found a second life as an acne treatment for adult women. Androgens drive oil production in the skin, and blocking them at the level of the sebaceous gland reduces sebum output and, with it, breakouts. At the doses used for acne (typically 150 mg per day or less), spironolactone largely loses its diuretic effect but retains its anti-androgen activity.¹¹

The SAFA trial, a large randomized controlled trial conducted in England and Wales, found that women taking spironolactone for acne reported greater improvements in acne-related quality of life compared with those on placebo, with the difference growing more pronounced over time. By 24 weeks, the gap between spironolactone and placebo was clinically meaningful, and participants on spironolactone were more likely to report visible improvement when comparing photos.¹² The FASCE trial compared spironolactone head-to-head with doxycycline, a commonly prescribed antibiotic for acne, and found that spironolactone performed better at four months and was nearly three times more likely to produce treatment success at six months.¹³ Despite these results, spironolactone remains officially off-label for acne in most countries, meaning it has not received regulatory approval specifically for that purpose. Dermatologists prescribe it anyway, widely and routinely.

Excess Hair Growth in Women

The same anti-androgen mechanism that clears acne also slows unwanted hair growth. In women with hirsutism (excessive hair growth in a male-type pattern, such as the face, chest, or abdomen), spironolactone at 200 mg per day produced clear improvement in facial hair quantity and quality in 19 out of 20 patients in one early study. Changes in hair diameter, density, and growth rate became noticeable within two months.¹⁴ A Cochrane review of the available evidence concluded that spironolactone is an effective treatment for reducing the degree of hirsutism, though it noted the studies available were relatively limited in size and quality.¹⁵ In practice, dermatologists and endocrinologists commonly pair spironolactone with other approaches like laser hair removal or oral contraceptives for women with polycystic ovary syndrome-related hirsutism.

Gender-Affirming Hormone Therapy

Spironolactone is one of the most commonly used anti-androgens in feminizing hormone therapy for transgender women, particularly in the United States and Australia. Its role is to suppress testosterone’s effects while estradiol promotes feminizing changes. However, it may not be the most potent option. A cross-sectional study comparing transgender women on estradiol alone, estradiol plus spironolactone, or estradiol plus cyproterone acetate found that median testosterone levels were substantially lower in the cyproterone group (0.8 nmol/L) than in the spironolactone group (2.0 nmol/L), and this difference persisted after adjusting for dosing and other variables.¹⁶ Cyproterone acetate is unavailable in the United States, which partly explains why spironolactone dominates prescribing there despite potentially being less effective at testosterone suppression.¹⁷

Side Effects Worth Knowing About

The most clinically important side effect of spironolactone is hyperkalemia, an elevation of potassium in the blood that can, in serious cases, cause dangerous heart rhythm problems. This risk is highest in people with kidney impairment, older adults, and anyone taking other medications that also raise potassium. The prescribing information calls for potassium monitoring within a week of starting or adjusting the dose.¹⁸ In young, otherwise healthy women taking low doses for acne, the actual risk of dangerous hyperkalemia is low, but clinicians still typically check bloodwork periodically, especially at the start of treatment.

The anti-androgen effects that make spironolactone useful for acne and hirsutism are unwelcome side effects for men. Gynecomastia, the growth of breast tissue, is one of the best-known adverse effects in male patients. Case reports describe painful breast swelling developing after months of use, which typically resolves after stopping the drug. This side effect has historically limited spironolactone’s use in men, particularly at higher doses or with long-term treatment.

Other common complaints include menstrual irregularities in premenopausal women, breast tenderness, fatigue, and dizziness (especially when standing up quickly, due to the blood pressure-lowering effect). Most of these are dose-dependent and manageable with dose adjustment.

Drug Interactions and Dietary Cautions

Because spironolactone raises potassium levels, the most dangerous interactions are with other drugs that do the same thing. Combining it with ACE inhibitors, angiotensin receptor blockers (ARBs), potassium supplements, certain antibiotics like trimethoprim, NSAIDs, or beta-blockers can amplify the hyperkalemia risk.¹⁹ Patients with chronic kidney disease are at particular risk when these combinations stack up.²⁰

Diet matters too, and in a way that catches some people off guard. Potassium-containing salt substitutes, sold as a heart-healthy alternative to regular table salt, can push potassium levels to dangerous heights when combined with spironolactone. Case reports have documented severe hyperkalemia and serious heart rhythm disturbances in patients who used these substitutes liberally while on spironolactone, particularly when kidney function was already compromised.²¹ If you are taking spironolactone, it is worth checking the label of any “lite” or “reduced sodium” salt in your kitchen, as many contain potassium chloride.

Pregnancy and Reproductive Safety

Spironolactone is not recommended during pregnancy. The concern is straightforward: the same anti-androgen activity that treats acne and hirsutism could interfere with the sexual development of a male fetus. Animal studies have shown feminization of male offspring exposed to the drug in utero, and while human data are limited, the theoretical risk is considered serious enough that pregnancy is treated as a firm contraindication.²² ²³ For women of childbearing age who are prescribed spironolactone for any reason, reliable contraception is strongly encouraged. In dermatology, spironolactone is often co-prescribed with an oral contraceptive, which serves the dual purpose of acne treatment and pregnancy prevention.

How Eplerenone Compares

Eplerenone is a newer, more selective mineralocorticoid receptor antagonist that was developed partly to avoid spironolactone’s anti-androgen side effects. It blocks aldosterone receptors but has much less affinity for androgen and progesterone receptors, which means it does not cause gynecomastia or menstrual changes at anywhere near the same rate. The trade-off is that it is less potent at the mineralocorticoid receptor itself and generally more expensive.

In heart failure, eplerenone has its own landmark trial data. A comparative study found that patients on eplerenone had lower cardiovascular mortality and all-cause mortality than those on spironolactone, with the eplerenone group showing about half the cardiovascular death rate.²⁴ Whether this reflects a genuine pharmacological advantage or differences in patient selection and tolerability is still debated. In practice, many cardiologists reserve eplerenone for male patients who develop gynecomastia on spironolactone, or for patients who cannot tolerate the older drug’s side effect profile. For dermatological uses like acne and hirsutism, eplerenone is not a substitute, precisely because it lacks the anti-androgen effects that make spironolactone useful for those conditions.

Why One Drug Ends Up in So Many Medicine Cabinets

Spironolactone’s trajectory from a niche diuretic to a drug prescribed across cardiology, dermatology, endocrinology, hepatology, and transgender medicine is unusual in pharmacology. The discovery of aldosterone in 1953 led researchers to test synthetic steroids for their ability to block its effects, and the 17-spirolactone steroids emerged as effective antagonists by the late 1950s. Within a few years of the first case of primary aldosteronism being described, spironolactone was already being used to manage it. Its anti-androgen properties were not the reason it was created, but they turned out to be at least as consequential as its original purpose. Few drugs have had their off-label uses grow to rival, and in terms of patient volume arguably eclipse, their on-label ones. A teenager prescribed Aldactone for acne and a 70-year-old prescribed the identical pill for heart failure are both benefiting from different facets of the same molecule’s wide reach across hormone systems.