Myo-Inositol
A naturally occurring sugar alcohol produced in the body and found in many foods. Often called 'vitamin B8' though it's not technically a vitamin. Most relevant for women with polycystic ovary syndrome (PCOS) — a condition affecting roughly 10% of women that involves insulin resistance and is strongly linked to obesity. The 2023 international PCOS guidelines recommended myo-inositol as an alternative to metformin for some women. Evidence for weight loss in people without PCOS or insulin resistance is weak.
Quick read · 3 min
- •Evidence: Very weak — little to no reliable trial evidence
- •A 2023 systematic review and meta-analysis informing the International Evidence-Based PCOS Guidelines found that myo-inositol significantly reduced BMI and improved insulin resistance, testosterone, and menstrual regularity in women with PCOS.
- •Excellent safety record — myo-inositol is naturally present in food and produced by the body.
- •Unlike prescription drugs, supplements are not tested for effectiveness by the FDA before sale
Based on clinical trials · No rankings · Every claim linked to source
Last reviewed: March 2026
How it works
Inositol is a component of cell membrane signalling pathways, particularly those involved in insulin action. In insulin resistance, the cellular response to insulin is impaired — cells can't efficiently take up glucose, leading to higher insulin levels and fat storage. Myo-inositol appears to improve insulin signalling at the cellular level, effectively enhancing the body's sensitivity to its own insulin. This reduces circulating insulin, which in turn can reduce fat storage and appetite signals. A 40:1 ratio of myo-inositol to D-chiro-inositol is thought to best replicate the body's natural balance.
What the evidence shows
A 2023 systematic review and meta-analysis informing the International Evidence-Based PCOS Guidelines found that myo-inositol significantly reduced BMI and improved insulin resistance, testosterone, and menstrual regularity in women with PCOS. It was recommended as an alternative to metformin in women who cannot tolerate metformin. In non-PCOS populations, evidence for weight loss is weaker — a broader 2024 meta-analysis found BMI reductions that were most pronounced in people with PCOS or overweight/insulin resistance. If you have PCOS, the evidence is notably stronger than if you don't.
The trade-off
What this tends to offer:
- ✓Strong evidence for insulin sensitivity improvement in PCOS
- ✓Modest weight loss observed in PCOS-specific trials
- ✓Generally well-tolerated at standard doses
- ✓Affordable (~$15–$30/month)
What this involves:
- •Benefits are primarily relevant for PCOS/insulin resistance
- •Much weaker evidence for weight loss without PCOS
- •Requires consistent daily dosing (2–4g)
- •GI effects (bloating, gas) at higher doses
Safety
Excellent safety record — myo-inositol is naturally present in food and produced by the body. Side effects are very rare at typical doses (2–4 g/day) and are usually mild GI symptoms (nausea, gas). Safe in pregnancy — it has actually been studied for gestational diabetes prevention with a good safety profile. Much better tolerated than metformin, which causes GI side effects in about 30% of users. No significant drug interactions documented.
Community insights
These are personal experiences shared in public online communities — not medical advice.
“If you have PCOS, this is one of the supplements most worth discussing with your doctor — the evidence is genuinely better than most supplements in this category, and it was included in the 2023 international PCOS treatment guidelines.”
“Many people use the 40:1 myo-inositol to D-chiro-inositol ratio — this mimics the natural ratio found in the body and appears in several studies. Products combining both are widely available.”
“If you're not responding to just myo-inositol, combining with 200 mcg of chromium picolinate is supported by some trial data for blood sugar regulation in PCOS.”
Common questions
After reading this page, most people compare this with other supplements, look at prescription options, or check what they can do today without a prescription.