Spironolactone
Is It Right for You?
A complete guide to Spironolactone — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Spironolactone?
Spironolactone is an orally administered potassium-sparing diuretic and aldosterone antagonist with a broad range of clinical applications spanning cardiology, endocrinology, nephrology, and dermatology. It was first synthesised in the late 1950s and has been in continuous clinical use for over six decades, accumulating one of the most extensive evidence bases of any prescription drug.
Structurally, spironolactone is a synthetic steroidal compound that competitively inhibits the mineralocorticoid receptor (aldosterone receptor) in the distal nephron of the kidney, reducing sodium and water reabsorption while sparing potassium excretion. In addition to its diuretic mechanism, spironolactone and its active metabolite canrenone possess significant anti-androgenic properties — they compete with testosterone and dihydrotestosterone (DHT) at androgen receptors and reduce androgen synthesis — a mechanism that underpins its growing use in conditions driven by androgen excess including acne, hirsutism, and female pattern hair loss.
Spironolactone is available generically and supplied in 25 mg, 50 mg, and 100 mg tablets. It is taken orally with or after food.
What Conditions Does Spironolactone Treat?
Spironolactone is prescribed for:
Spironolactone (and its more selective successor eplerenone) is a cornerstone pharmacotherapy for heart failure with reduced ejection fraction. In heart failure, chronic activation of the renin-angiotensin-aldosterone system (RAAS) leads to aldosterone excess, driving sodium and water retention, potassium and magnesium wasting, myocardial fibrosis, and ventricular remodelling. The landmark RALES trial (1999) demonstrated that adding spironolactone to standard heart failure therapy (ACE inhibitor, loop diuretic, digoxin) reduced all-cause mortality by 30% and heart failure hospitalisations significantly in patients with severe HFrEF. It is now standard of care in patients with HFrEF alongside ACE inhibitors or ARBs, beta-blockers, and SGLT2 inhibitors.
Primary hyperaldosteronism — excess aldosterone production by the adrenal glands, most commonly from a unilateral adenoma (Conn's adenoma) or bilateral adrenal hyperplasia — causes hypertension, hypokalaemia, and sodium retention. Spironolactone is the treatment of choice for bilateral adrenal hyperplasia and is also used for pre-operative management of unilateral adenoma before adrenalectomy. It directly antagonises the excess aldosterone, correcting hypokalaemia and controlling blood pressure.
Spironolactone is a highly effective fourth-line antihypertensive agent in patients whose blood pressure remains uncontrolled despite three standard antihypertensive drugs. Its mechanism in resistant hypertension involves aldosterone antagonism and sodium excretion, and a large proportion of patients with apparent treatment-resistant hypertension have unsuppressed aldosterone as a contributing factor. The PATHWAY-2 trial demonstrated that spironolactone 25–50 mg was superior to doxazosin and bisoprolol as fourth-line therapy in resistant hypertension.
Chronic liver disease leads to portal hypertension and RAAS activation, causing sodium retention, ascites, and peripheral oedema. Spironolactone is the diuretic of choice for managing ascites in cirrhosis, typically in combination with a loop diuretic (furosemide) in a ratio of approximately 100 mg spironolactone to 40 mg furosemide, titrated to achieve gradual weight loss while minimising electrolyte disturbance.
Spironolactone may be used in combination with other diuretics to manage oedema in nephrotic syndrome, where hypoalbuminaemia-driven sodium retention is a central pathophysiological mechanism.
Spironolactone's anti-androgenic properties make it an effective treatment for hormonally driven acne in women, particularly when acne is inflammatory, predominantly affects the lower face and jawline, worsens premenstrually, or has failed to respond adequately to standard topical treatments and antibiotics. By reducing androgen receptor stimulation and androgen synthesis, spironolactone decreases sebum production and normalises follicular keratinisation — both central to acne pathogenesis. Evidence from clinical trials and large observational studies consistently supports its use in this context. UK dermatology guidelines increasingly recognise spironolactone as an important option for women with hormonal acne, particularly as an alternative to prolonged antibiotic use.
The same anti-androgenic mechanism makes spironolactone useful in the treatment of female pattern hair loss and hirsutism (excess facial or body hair in women), both of which are driven by androgen sensitivity of hair follicles. It is used off-label for these indications in women, typically at doses of 100–200 mg daily.
Spironolactone is widely used in feminising hormone therapy for transgender women as an androgen blocker, reducing testosterone-driven masculinising effects prior to or alongside oestrogen treatment. This is an off-label but well-established indication managed in specialist gender clinics.
While Spironolactone is effective for managing various conditions, it should be used cautiously in patients with renal impairment or those taking other medications that may interact.
How Does Spironolactone Work?
Aldosterone Antagonism (Diuretic and Cardiovascular Mechanism)
In the distal convoluted tubule and collecting duct of the kidney, aldosterone normally binds to mineralocorticoid receptors, promoting the insertion of sodium channels and sodium-potassium ATPase pumps into the tubular epithelium. This increases sodium reabsorption (retaining water) and increases potassium excretion into the urine. Spironolactone competitively blocks aldosterone at these receptors, reversing these effects: sodium and water are excreted (reducing blood pressure and oedema), and potassium is retained (which is clinically important — it can cause dangerous hyperkalaemia in susceptible patients). In the heart, aldosterone blockade reduces myocardial fibrosis, inflammation, and pathological ventricular remodelling, contributing to its mortality benefit in heart failure beyond simple diuresis.
Anti-Androgenic Mechanism (Dermatological and Endocrine Effects)
Spironolactone and its active metabolite canrenone bind to androgen receptors throughout the body, acting as competitive antagonists of testosterone and DHT. In addition, spironolactone reduces adrenal and gonadal androgen synthesis by inhibiting certain steroidogenic enzymes (17-hydroxylase, 17-20 lyase). In the skin, sebaceous glands, and hair follicles — tissues highly sensitive to androgen stimulation — this results in reduced sebum production, decreased follicular keratinocyte proliferation, and improved hair follicle cycling. These effects explain its clinical benefit in hormonally driven acne, hirsutism, and female pattern hair loss.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Spironolactone tablets should be taken with food, which improves absorption and reduces the risk of gastrointestinal upset. If taken once daily, a consistent time each day aids compliance. For conditions requiring doses above 100 mg, dividing the daily dose into two administrations may reduce side effects.
Side Effects of Spironolactone
Spironolactone is generally well tolerated, but some side effects may occur.
- Increased urination
- Dizziness or lightheadedness
- Breast tenderness or enlargement (gynecomastia)
- Menstrual irregularities (in women)
- Fatigue
- Hyperkalaemia (high potassium levels) — muscle weakness, irregular heartbeat
- Severe dehydration or low blood pressure — fainting, confusion
- Kidney problems — reduced urine output, swelling
- Severe allergic reaction — swelling of face, lips, or throat, difficulty breathing
Patients should be informed about the risk of hyperkalaemia and the importance of regular monitoring of potassium levels.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting Spironolactone
Important Warnings
High potassium levels can cause life-threatening cardiac arrhythmias. Electrolytes and renal function must be checked before starting treatment and monitored regularly thereafter, with frequency determined by baseline values, concurrent medications, and clinical stability. Patients should be advised to avoid potassium-containing salt substitutes and limit high-potassium foods if taking spironolactone at higher doses alongside other potassium-raising drugs.
Spironolactone must not be taken during pregnancy. Effective contraception is required throughout treatment and for at least one month after stopping. Advise patients to contact their clinician immediately if they think they may be pregnant.
Regular use of over-the-counter NSAIDs (ibuprofen, naproxen) by patients on spironolactone carries a significant risk of hyperkalaemia and renal impairment. Patients should avoid regular NSAIDs unless specifically advised otherwise by their clinician.
Speak to a Clinician About Treatment
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The treatment you need, when you need it.
Spironolactone FAQs
Improvement in hormonal acne with spironolactone is gradual. Most women begin to notice meaningful changes after 3 months of consistent use, with maximum benefit typically seen at 6 months. Because the mechanism targets androgen-driven sebum production and follicular cycling rather than bacteria, results are not immediate. Persistence is important — many women who persevere for 6 months achieve excellent long-term control.
Menstrual irregularity is a common side effect at higher doses, including spotting between periods, shorter or longer cycles, and occasionally amenorrhoea. These effects often settle over time. Women using spironolactone for acne are frequently prescribed a combined oral contraceptive pill concurrently, which regulates periods and provides contraception.
Men can take spironolactone for cardiac or blood pressure indications, but the anti-androgenic and pro-oestrogenic side effects (primarily gynaecomastia and breast tenderness) are much more bothersome in male patients. For these reasons, eplerenone — a more selective mineralocorticoid receptor antagonist without significant anti-androgenic activity — is often preferred in men when the primary indication is heart failure or hypertension. Spironolactone is not appropriate for male acne or hair loss treatment.
Paradoxically, spironolactone is used to treat female pattern hair loss. It does not typically cause hair loss. In men, however, anti-androgenic effects could theoretically affect androgen-dependent hair, but this is not a standard concern at typical therapeutic doses.
Alcohol can enhance the blood-pressure-lowering and diuretic effects of spironolactone, increasing the risk of dizziness, dehydration, and hypotension. Moderate alcohol consumption is generally not prohibited, but patients should be aware of additive hypotensive effects, particularly when standing up.