Clinical comparison · PCOS & fertility · Updated 2026-07-02
Metformin is an insulin sensitizer; letrozole is an aromatase inhibitor used to induce ovulation. This table reproduces labeled and trial-reported facts verbatim, per cell. They target different problems (insulin resistance vs ovulation), so their 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 | Letrozole |
|---|---|---|
| Drug class | Biguanide (insulin sensitizer)[1] | Aromatase inhibitor[2] |
| Primary PCOS role | Insulin resistance and metabolic support[3] | Ovulation induction[2] |
| Reported outcome | Improves ovulation and pregnancy rates vs placebo (Cochrane)[3] | 27.5% live-birth rate vs clomiphene 19.1% in PPCOS II[4] |
| Most common side effect | Diarrhea 53.2% (monotherapy)[1] | Hot flashes/flushes 33.5% (Femara label)[2] |
| Typical dosing | Target 1,500-2,000 mg/day (titrated)[1] | 2.5 mg daily for 5 days each cycle[2] |
| Pregnancy handling | Sometimes continued under specialist care (historical category B)[1] | Taken before conception and stopped; not used in established pregnancy[2] |
Different targets, not comparable
The Cochrane metformin review measured ovulation and pregnancy rates for a metabolic drug; PPCOS II measured live-birth rate for an ovulation-induction drug. The two address different mechanisms and cannot be read as a head-to-head. Cochrane — Metformin for PCOS
No. Metformin targets insulin resistance and metabolic factors, while letrozole is used to induce ovulation (Cochrane; FDA Femara label).
Not necessarily. Metformin is sometimes continued under specialist care, whereas letrozole is taken before conception and then stopped (FDA labels).
Editorial reviews from ClearHormones of telehealth providers in this category. These are not treatment recommendations, and prescribing decisions rest with a licensed clinician.