Spironolactone side effects

At the doses used for acne and hair loss, the most common spironolactone side effects are headache, dizziness, irregular periods and breast tenderness, and most are mild. High potassium is the warning on the label, but in healthy young women it turned up no more often than in women not taking the drug; the risk rises with age, kidney problems and certain other medicines.

Spironolactone is FDA-approved for heart failure, high blood pressure, some kinds of edema and primary hyperaldosteronism. Prescribing it for female pattern hair loss or acne is off-label. It is a generic, non-controlled drug, and clinicians use it for these conditions because it blocks some of the effects of androgens (male-type hormones). Here is what the label and the trials in women show, side effect by side effect.

What the label lists

The label’s warnings cover four areas: high potassium (hyperkalemia), low blood pressure and worse kidney function from fluid loss, other salt and metabolic changes, and breast enlargement in men. It is contraindicated in people with high potassium, Addison’s disease or who take eplerenone. The current Aldactone label has no boxed warning.

Its list of reported reactions, without frequencies, includes:

• Reproductive: irregular periods or no periods, bleeding after menopause, breast and nipple pain, decreased libido and, in men, trouble getting or keeping an erection
• Nervous system: dizziness, headache, drowsiness, lethargy, confusion and unsteadiness
• Digestive: nausea, vomiting, diarrhea and cramping, gastritis and, rarely, stomach bleeding or ulcers
• Muscles: leg cramps
• Skin: itching, hair loss (alopecia) and, rarely, severe reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis and DRESS
• Blood and liver: low white cell or platelet counts, and a very few cases of liver injury, one of them fatal

The label lists these from clinical trials and postmarketing reports, so it cannot say how often each happens or whether the drug caused it in every case.

What women in the trials reported

The best placebo-controlled data at acne doses come from SAFA, a 2023 UK trial of 410 women who took 50 mg a day for 6 weeks, then 100 mg a day to week 24 (Santer et al.). Women answered a questionnaire on side effects throughout:

Women on spironolactone were more likely to report at least one adverse reaction (64% vs 51%), but among single side effects only the headache difference was statistically significant, and there were no serious adverse reactions. Many effects were common on placebo too, which is why a trial with a placebo group matters: the share of women who felt dizzy on spironolactone was 7 points higher than on placebo, not 19.

Period changes

Irregular bleeding barely differed in SAFA, but SAFA let women keep their usual contraception. The picture changes without the pill. In a 2025 Thai trial for female pattern hair loss that excluded hormonal contraceptive users, 9 of 24 women (37.5%) on 100 mg a day had irregular periods, the only side effect significantly more common than on placebo, and 2 stopped because of it (Werachattawatchai et al.). In a case series of 403 women taking spironolactone long term for acne, period side effects were less common among those using a combined oral contraceptive (odds ratio 0.23) (Garg et al.).

The SAFA authors also suggested that period problems may be more a feature of higher doses. If you have spotting or shorter cycles, your prescriber may adjust the dose or suggest contraception, which you need anyway because of the pregnancy risk below.

Potassium: who needs blood tests

Spironolactone keeps potassium in the body. The label says it can cause high potassium, especially with kidney problems, potassium supplements, salt substitutes, or drugs such as ACE inhibitors, angiotensin receptor blockers, NSAIDs, trimethoprim and heparin, and it says to check potassium within 1 week of starting or changing the dose and regularly after. That advice is written for the label’s approved uses, mostly older patients with heart, liver or kidney disease.

Two studies show how the risk differs in women taking it for skin and hair:

• Healthy young women: among 974 women taking spironolactone for acne, 13 of 1,802 potassium tests (0.72%) were high, the same as the 0.76% background rate in similar women, and the authors concluded routine monitoring was unnecessary in that group (Plovanich et al.).
• Women 45 and older: in 398 women taking it for skin or hair conditions, 10.1% developed high potassium, rising to 22.4% at 65 and older and 28.1% at 65 and older with a related health condition. Nearly all cases (97.5%) were mild and 85% caused no symptoms (Gregoire et al.).

Your prescriber decides whether you need tests. Tell them your age, any kidney problems, and every medicine and supplement you take.

Dizziness and blood pressure

Spironolactone is a diuretic, so it can lower blood pressure and cause dehydration, particularly in people low on salt or taking ACE inhibitors or angiotensin receptor blockers, the label says. Tell your prescriber if you feel lightheaded.

This matters for hair loss, where it is often paired with low-dose oral minoxidil, another blood pressure drug. In 432 women taking both, dizziness, lightheadedness or feeling faint on standing affected 12.0%, and taking at least one more blood pressure drug raised the odds of those effects (odds ratio 3.29). Most effects were mild and managed without a hospital visit (Dewey et al.).

Breast changes, and side effects in men

Breast tenderness is common in women. In men, spironolactone can cause breast enlargement (gynecomastia): about 9% of men in the RALES heart failure trial developed it on a mean dose of 26 mg a day. The label says the risk rises with dose, onset ranges from 1 to 2 months to over a year, and it is usually reversible. Decreased libido and erection problems are also listed. Because of these effects, spironolactone is mainly a treatment for women; men with hair loss usually start with finasteride or minoxidil.

Pregnancy

Avoid spironolactone if you are pregnant or could become pregnant without contraception. The label says that, based on how it works and on animal studies, it may affect the sexual development of a male fetus; in rats, it feminized male fetuses. The SAFA trial required women at risk of pregnancy to use contraception during treatment and for at least 4 weeks after.

Spironolactone 25 mg and other doses

Aldactone comes as 25 mg, 50 mg and 100 mg tablets. The 25 mg tablet is round, light yellow and film-coated, and only the 50 mg and 100 mg tablets are scored for splitting. On the label, 25 mg once a day is the heart failure starting dose, and blood pressure starts at 25 to 100 mg.

Off-label doses for skin and hair run higher. SAFA used 50 mg, then 100 mg a day for acne. The 2025 hair loss trial used 100 mg, and its authors put the usual alopecia dose at about 100 to 200 mg a day. An older Australian study treated 40 women with spironolactone 200 mg a day and 40 with another anti-androgen, cyproterone acetate, for at least 12 months. Across both groups combined, 44% had regrowth, 44% no clear change and 12% continued loss, and there was no placebo group (Sinclair et al.). Your prescriber sets the dose, often starting lower and raising it, and side effects such as breast changes rise with dose.

Interactions to mention

Beyond the potassium-raising drugs above, the label flags lithium (higher lithium levels), NSAIDs (a weaker diuretic effect), aspirin, cholestyramine, digoxin blood tests, the prostate cancer drug abiraterone and mitotane. The label’s patient advice is to avoid potassium supplements and foods high in potassium, including salt substitutes, so give your prescriber the full list of what you take.

When to call your prescriber

• A high potassium result, or a new prescription for a drug that raises potassium
• Fainting, severe dizziness, confusion or very little urine
• A rash with blistering, peeling or fever
• A missed period or a positive pregnancy test
• Breast lumps, or more shedding than before you started

Getting it prescribed and what it costs

Online providers we compare list spironolactone for hair loss at $42 to $59 a month as of October 2026: Happy Head’s oral spironolactone at $42 ($34 a month on a 12-month supply), RxSpan MD’s spironolactone tablets at $59 with the consult included, and Strut Health’s women’s topical formula at $59. Happy Head’s capsule and Strut’s topical are compounded, so they are not FDA-approved. For acne, Nurx lists generic tablets at $15 a month ($45 per 3-month supply, plus a $40 consult), and Wisp lists oral spironolactone from $24.

See the spironolactone for hair loss and spironolactone for acne pages for the full label summaries, read what the SAFA trial found in our spironolactone for acne guide, and compare providers on our best hair loss treatment for women and online acne treatment lists.

The bottom line

At acne and hair loss doses, spironolactone’s common side effects are mild: headache, dizziness, more urine, breast tenderness and, especially without the pill, irregular periods. High potassium is rare in healthy young women but becomes more common after 45 and with kidney problems or potassium-raising drugs. Avoid it in pregnancy, and remember it is off-label for both hair loss and acne. Start at our hair loss hub if you are weighing it against minoxidil for women.