Inositol vs Metformin
The PCOS decision most often made without a clinician on one side and with one on the other — and the guideline is more specific than either camp usually admits.
Inositol
Myo-inositol, D-chiro-inositol
Improves menstrual-cycle regularity in pooled PCOS trials, but the 2023 international guideline graded the evidence very low certainty — live birth is unproven and the 40:1 ratio is unvalidated in humans.
Full Inositol evidence reviewMetformin
An approved diabetes drug with an intriguing longevity hypothesis — but the dedicated aging trial (TAME) is still pending; longevity in healthy people is unproven.
Full Metformin evidence reviewSide by side
| Inositol | Metformin | |
|---|---|---|
| Marketed for | PCOS, insulin sensitivity, fertility, anxiety | Longevity, healthspan, metabolic aging |
| Evidence grade | Clinical data | Clinical data |
| Family | Metabolic / AMPK | Metabolic / AMPK |
| Key human source | Guideline systematic review, JCEM 2024 | MILES/TAME rationale 2014 |
marks a row where the two differ. Evidence grades come from our evidence matrix, which grades each molecule on the human data for the use it is marketed for.
Our verdict
For cycle regularity the gap is smaller than the prescription-versus-supplement framing suggests: a meta-analysis of 26 randomized trials in 1,691 women found inositol raised the chance of a regular menstrual cycle by a factor of 1.79 versus placebo and was non-inferior to metformin on that outcome, with fewer gastrointestinal side effects. The certainty is the catch. The systematic review behind the 2023 international PCOS guideline read 30 trials in 2,230 participants, called the evidence limited and inconclusive, graded the inositol recommendation very low certainty, and preferred metformin where hirsutism and central adiposity are the concern. Live birth remains genuinely uncertain for inositol on Cochrane's reading of 13 trials. Metformin is also sold separately as a longevity drug, which is a different and still-unproven claim — TAME has not reported.
Inositol fits if
Cycle regularity is the goal, tolerability matters to you, and you accept a guideline grading of very low certainty on a compound you can buy without a prescription.
Metformin fits if
Hirsutism or central adiposity is the concern, or you want the option with guideline preference and an approved-drug evidence base — and you have a clinician to prescribe and monitor it.