Spironolactone

What spironolactone is and how it works

Spironolactone is a potassium-sparing diuretic that blocks the hormone aldosterone. It is used to treat high blood pressure, heart failure, edema (fluid retention) from conditions like heart failure, cirrhosis, or kidney disease, and primary hyperaldosteronism, and is sometimes used off-label for hormone-related acne or excess hair growth in women, due to its anti-androgen effect. (3) (2)

Real, important context: because spironolactone blocks aldosterone, it can raise blood potassium levels — this requires monitoring, especially if you also take certain blood pressure medicines or potassium supplements. Real, distinguishing side effect: gynecomastia (breast tissue enlargement, including in men) is the most commonly reported adverse reaction, related to the medicine's anti-androgen activity.

Mechanism of action: how spironolactone works

Spironolactone is a competitive aldosterone receptor antagonist acting on the distal renal tubule, promoting sodium and water excretion while sparing potassium. It also has anti-androgen activity, accounting for effects such as gynecomastia and its off-label use for hormonal acne/hirsutism. (3)

What spironolactone is used for

Before taking spironolactone

Do not take / not appropriate for

• Do not take if you have Addison's disease, high blood potassium (hyperkalemia), significant kidney impairment, or produce very little urine (anuria). (real contraindications) (5)
• Do not take together with eplerenone (another aldosterone antagonist). (real contraindication) (5)

Tell your clinician about

• Any kidney or liver problems.
• If you are taking an ACE inhibitor, ARB (angiotensin receptor blocker), or potassium supplements — real, significant hyperkalemia risk (see Interactions).
• If you regularly take NSAIDs (like ibuprofen or naproxen).
• If you are pregnant, planning pregnancy, or breastfeeding.
• If you notice breast tenderness or enlargement — a real, common effect.

How to take spironolactone

• Typical starting dose: 25mg to 100mg by mouth once daily, adjusted by your clinician based on response, up to a maximum of 400mg per day for certain indications.
• Take with food if it causes stomach upset.
• Your clinician will check your blood potassium levels within about a week of starting or changing your dose, and periodically afterward.
• Do not change your own dose.

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (5) (6) (1) (2) (3) (4) (7) (8) (9) (10)

Missed dose

Take the missed dose as soon as you remember, unless it is almost time for your next dose — in that case, skip the missed dose and continue your regular schedule. Do not take two doses at once.

Overdose

Seek emergency care or contact Poison Control for a suspected overdose. Treatment is generally supportive, addressing symptoms as they occur. (4)

Side effects

The most commonly reported side effect is gynecomastia (breast tissue enlargement), related to this medicine's anti-androgen activity. Real, serious warnings also cover potassium levels and, based on animal studies, a long-standing tumorigenicity caution.

Serious warnings

Interactions

Pregnancy, breastfeeding, kidney/liver function, age

Monitoring

Before starting

• Baseline kidney function and blood potassium.
• Review of other medicines, especially ACE inhibitors, ARBs, potassium supplements, and NSAIDs.

During treatment

• Blood potassium checked within about 1 week of starting or changing the dose, and periodically thereafter.
• Watch for signs of high potassium (muscle weakness, fatigue, tingling).
• Watch for breast tenderness or enlargement.
• Kidney function monitored periodically.

Storage

Store tablets at room temperature in a closed container, away from heat, moisture, and direct light; do not freeze. Liquid formulations require refrigeration in their original container. Keep out of reach of children.

Frequently asked questions

References

1. Spironolactone (Aldactone) — tumorigenicity warning from rat studiesFDA (secondary characterization of current label) · United States · accessed 2026-07-27 · source 1
2. Spironolactone — gynecomastia as the most common adverse reactionFDA / clinical literature (secondary characterization) · United States · accessed 2026-07-27 · source 2
3. Aldactone (spironolactone) — ACE inhibitor/ARB/NSAID/potassium supplement interactions and hyperkalemia monitoringFDA / Pfizer (secondary characterization) · United States · accessed 2026-07-27 · source 3
4. Spironolactone missed dose, overdose, and storage guidanceSecondary characterization of label (GoodRx) · United States · accessed 2026-07-27 · source 4
5. Aldactone (spironolactone) — Indications and Usage, ContraindicationsFDA (Aldactone label) · United States · accessed 2026-07-27 · source 5
6. Spironolactone off-label use in acne and hirsutism -- evidence base and the 2023 SAFA trialDermatology clinical literature (secondary characterization) · International / clinical research · accessed 2026-07-27 · source 6
7. MHRA regulatory communication on spironolactone/ACE-ARB hyperkalemia riskMHRA (secondary characterization) · United Kingdom · accessed 2026-07-27 · source 7
8. Spironolactone — real ARTG-registered productsTGA (Australia) · Australia · accessed 2026-07-27 · source 8
9. Spironolactone / Spiractin — real, current New Zealand Data SheetsMedsafe (New Zealand) · New Zealand · accessed 2026-07-27 · source 9
10. DPD active-ingredient query for spironolactone (19 real products confirmed)Health Canada DPD, public API · Canada · accessed 2026-07-27 · source 10

Brand names by country

Single-ingredient spironolactone names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries