Spironolactone

is prescribed to treat:

• Heart failure (reduces mortality and hospitalizations) • High blood pressure (hypertension) • Edema (fluid retention) from various causes • Primary hyperaldosteronism • Cirrhosis with ascites • Nephrotic syndrome • Hormonal acne in women (off-label) • Polycystic ovary syndrome (PCOS) symptoms (off-label) • Hirsutism (excessive hair growth in women) (off-label)

It helps remove excess fluid while retaining potassium.

Spironolactone (Aldactone) is a mineralocorticoid receptor antagonist used in heart failure with reduced ejection fraction, in resistant hypertension, in cirrhosis with ascites, and — off-label but very widely — in acne and hirsutism in women, particularly with PCOS. It is a diuretic whose most important benefits are not diuretic at all.

Mechanism of Action

Spironolactone competitively blocks the mineralocorticoid receptor, preventing aldosterone from acting on the distal tubule and collecting duct. The immediate result is reduced sodium reabsorption and reduced potassium excretion — hence potassium-sparing diuresis, a weak natriuretic effect compared with a loop diuretic such as furosemide.

The diuretic effect, however, is not why it saves lives in heart failure. Aldosterone drives myocardial and vascular fibrosis, endothelial dysfunction, and adverse remodelling independent of its effect on sodium. Blocking that signal reduces mortality in heart failure with reduced ejection fraction at doses far below those needed for meaningful diuresis. This is why spironolactone appears in heart failure regimens at a low fixed dose rather than being titrated to urine output.

Spironolactone also binds androgen and progesterone receptors, which is a side effect in men and the entire therapeutic point in women treated for acne or hirsutism. Anti-androgen activity produces gynecomastia, breast tenderness, and erectile dysfunction in men — the most common reason male patients stop it. Eplerenone is more selective for the mineralocorticoid receptor and is the alternative when these effects are limiting, at higher cost.

Clinical Use

In heart failure with reduced ejection fraction, spironolactone is one of the four foundational therapies alongside a beta blocker, a renin-angiotensin agent, and an SGLT2 inhibitor. In resistant hypertension — blood pressure uncontrolled on three agents including a diuretic — it is the best-evidenced fourth-line drug and frequently the one that finally achieves control, because unrecognised aldosterone excess is a common underlying cause. A patient on three drugs with poor control deserves consideration of spironolactone before a fourth agent from another class.

In cirrhosis with ascites it is the diuretic of choice, because portal hypertension drives secondary hyperaldosteronism and blocking that axis directly addresses the mechanism.

The dermatologic and endocrine use in women is substantial and generally well tolerated: it reduces sebum production and hirsutism through androgen blockade. Effect takes several months, and patients told to expect improvement in weeks conclude it has failed. It is used with contraception given the teratogenic risk to a male fetus. Our cardiovascular team manages the heart failure and hypertension indications, and the MedlinePlus spironolactone entry covers prescribing detail.

Monitoring and Follow-Up

Potassium and kidney function are the monitoring priorities and the checks are not optional. Measure both at baseline, within one week of starting or any dose increase, again at one month, and periodically thereafter.

Hyperkalemia is the serious risk and can be fatal. It becomes far more likely with reduced kidney function, in diabetes, in older adults, and — critically — when spironolactone is combined with an ACE inhibitor or ARB, which is exactly the combination heart failure guidelines recommend. That combination is correct and beneficial, but it makes monitoring mandatory rather than advisory. Potassium supplements and salt substitutes, which are potassium chloride, should be stopped.

Gynecomastia and breast tenderness in men are dose-related and often develop over months. Menstrual irregularity is common in women. Both are worth asking about directly, since patients frequently stop the drug rather than report them. The heart failure early signs article covers what decompensation looks like, and the American Heart Association provides patient background.

Resistant hypertension deserves a closer look before a fourth drug is chosen at random. True resistance — uncontrolled pressure on three agents at adequate doses including a diuretic — should prompt a check for the common mimics first: white coat effect, poor adherence, NSAIDs, excess salt, alcohol, and untreated sleep apnea. Once those are excluded, primary aldosteronism is far more common than historically assumed, and spironolactone addresses it directly. The white coat and masked hypertension article covers why office readings alone mislead, and confirming resistance with home or ambulatory readings before escalating avoids treating a measurement artefact with a fourth medication.

Special Populations

In older adults, hyperkalemia risk is substantially higher and kidney function is often worse than creatinine suggests; start low and check potassium sooner. In significant kidney impairment spironolactone is generally avoided, and it is contraindicated in severe impairment, anuria, and pre-existing hyperkalemia.

In pregnancy it is avoided because of anti-androgen effects on a male fetus. Any woman of reproductive potential taking it for acne or hirsutism needs reliable contraception and an explicit conversation about why. NSAIDs blunt the effect and add to hyperkalemia and kidney injury risk, particularly alongside an ACE inhibitor or ARB. Trimethoprim, including in trimethoprim-sulfamethoxazole, raises potassium independently and is a recognised precipitant of dangerous hyperkalemia in patients on spironolactone — a common outpatient antibiotic pairing worth checking before prescribing.

Timing helps with one common complaint. Spironolactone is a weak diuretic, but it still increases urine output, and an evening dose disrupts sleep in some patients. Taking it in the morning generally solves this. Its onset is also slow relative to a loop diuretic, taking days rather than hours to reach full effect, so it should not be judged on the first day.

When to Contact Your Doctor

Report muscle weakness, fatigue, palpitations, an irregular or slow heartbeat, or tingling around the mouth or in the extremities — these can indicate hyperkalemia and warrant same-day potassium testing rather than waiting.

Any illness causing vomiting, diarrhea, or reduced fluid intake is a reason to ask whether spironolactone and other diuretics should be held temporarily, since dehydration and kidney injury drive potassium up quickly. Report breast tenderness or enlargement, menstrual changes, or sexual dysfunction rather than stopping the drug silently — there are alternatives. Confirm before starting any new antibiotic or NSAID.

To review your potassium, your heart failure regimen, or side effects that are making treatment hard to continue, contact us or schedule a visit.