Clinical comparison · PCOS & fertility · Updated 2026-07-02
Metformin is an insulin sensitizer; spironolactone is an anti-androgen used off-label for PCOS skin and hair symptoms. This table reproduces labeled and trial-reported facts verbatim, per cell. They address different PCOS problems, so the outcomes are not directly comparable. The page does not rank them.
Every value below is reproduced verbatim from an FDA prescribing-information document or a published clinical trial, and each cell links to its source. This page does not rank the two options, does not declare one safer or more effective, and is not medical advice.
| Dimension | Metformin | Spironolactone |
|---|---|---|
| Drug class | Biguanide (insulin sensitizer)[1] | Aldosterone antagonist with anti-androgen effect[2] |
| Primary PCOS target | Insulin resistance and metabolic support[3] | Androgen-driven acne and hirsutism (off-label)[4] |
| Reported outcome | Improves ovulation and pregnancy rates vs placebo (Cochrane)[3] | Effective for adult female hormonal acne (Cochrane)[4] |
| Most common side effect | Diarrhea 53.2% (monotherapy)[1] | Increased urination (diuretic effect); irregular menses/breast tenderness reported[2] |
| Serious monitoring flag | Lactic acidosis (rare); periodic B12 on long-term use[1] | Hyperkalemia — monitor potassium[2] |
| Pregnancy handling | Sometimes continued under specialist care (historical category B)[1] | Avoided in pregnancy (anti-androgen); use effective contraception[2] |
Different targets, not comparable
The Cochrane metformin review measured ovulation and pregnancy rates; the Cochrane spironolactone review measured acne response. These are different PCOS symptoms and endpoints, so the results are not a head-to-head. Cochrane — Spironolactone for acne
Guideline context
The 2023 International PCOS Guideline discusses both agents within different symptom domains. This page reproduces numeric and labeled facts rather than guideline recommendations. International PCOS Guideline (2023)
No. Metformin targets insulin resistance, while spironolactone is used off-label for androgen-driven acne and hirsutism (Cochrane reviews; FDA labels).
The FDA Aldactone label flags hyperkalemia, so potassium monitoring is advised. Metformin's label notes rare lactic acidosis and periodic B12 checks on long-term use.
Editorial reviews from ClearHormones of telehealth providers in this category. These are not treatment recommendations, and prescribing decisions rest with a licensed clinician.