What this means in practice
If metformin is working and tolerable, the evidence does not support trading it for inositol. If the gastrointestinal effects are the reason it stopped being tolerable, inositol is the gentler option carrying weaker evidence, and that is a trade worth naming out loud with whoever prescribed the metformin rather than made quietly.
What people say
Inositol is the natural alternative to metformin. It does the same job without wrecking your stomach, so you can take it instead of the drug, or stack it on top for a stronger effect.
What the evidence supports
Pooling six trials of 388 women, adding inositol on top of metformin improved menstrual cycle regularity (RR 1.56, 95% CI 1.01 to 2.41) and lowered hirsutism score by about one point, while changing nothing on body mass index, fasting glucose or insulin resistance. Head to head, a meta-analysis of eight trials found no significant difference between myo-inositol and metformin on any metabolic or hormonal marker it measured. The tolerability claim is the part that holds: the 2023 guideline's evidence review found myo-inositol likely causes fewer gastrointestinal adverse events than metformin, and describes those events as typically mild and self-limiting. That same guideline still recommends metformin over inositol for hirsutism and central adiposity, and says metformin has greater efficacy overall.
How it is supposed to work
Both are described as insulin sensitisers acting at different points of the insulin signalling pathway, so taking them together is proposed to lower insulin resistance more than either does alone.
Which way it runs
Asymmetric in what has actually been tested. Trials added inositol on top of metformin and measured what changed, so the evidence runs in that direction. Nobody has run the trial people actually want, which is stopping metformin and taking inositol instead.
What is still missing
The swap people actually make has never been tested as a swap. What the trials tested was adding inositol to metformin, and what they found was a more regular month rather than a better outcome.
Sources
- Comparison of metformin with inositol versus metformin alone in women with polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trialsKelly FA, de Oliveira Macena Lobo A, Cardoso JHCO, de Moraes FCA, 2025
- Effects of myo-inositol vs. metformin on hormonal and metabolic parameters in women with PCOS: a meta-analysisFatima K, Jamil Z, Faheem S, et al., 2023
- Inositol for Polycystic Ovary Syndrome: A Systematic Review and Meta-analysis to Inform the 2023 Update of the International Evidence-based PCOS GuidelinesFitz V, Graca S, Mahalingaiah S, et al., 2024
- Comparative efficacy of oral insulin sensitizers metformin, thiazolidinediones, inositol, and berberine in improving endocrine and metabolic profiles in women with PCOS: a network meta-analysisZhao H, Xing C, Zhang J, He B, 2021
- Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary SyndromeTeede HJ, Tay CT, Laven JJE, et al., 2023
- Inositol is an effective and safe treatment in polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trialsGreff D, Juhasz AE, Vancsa S, et al., 2023
- Insulin-sensitising drugs (metformin, rosiglitazone, pioglitazone, D-chiro-inositol) for women with polycystic ovary syndrome, oligo amenorrhoea and subfertilityMorley LC, Tang T, Yasmin E, Norman RJ, Balen AH, 2017