Evidence explainerInositol
Inositol for PCOS: More Regular Periods in 26 Trials, With Real Caveats
Myo-inositol is the most-studied supplement for polycystic ovary syndrome. A 2023 meta-analysis found more regular cycles than placebo and results close to metformin, but most trials were small and one was later retracted.
Key takeaways
- In a 2023 meta-analysis of 26 trials (1,691 women with PCOS), regular periods were 1.79 times as likely with inositol as with placebo [1].
- Inositol was non-inferior to metformin for cycle regularity in that analysis [1].
- Testosterone, androstenedione and BMI fell more than with placebo, and SHBG rose [1].
- Most trials used 1,000 to 4,000 mg a day of myo-inositol for 7 to 24 weeks [1].
- Side effects were rare in a safety review; mild nausea, gas and diarrhea appeared only at 12 g a day [3].
The evidence, graded
Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.
- Grade BImprovedRegular menstrual periods in PCOSRegular periods were 1.79 times as likely as with placebo (95% CI 1.13–2.85), and inositol was non-inferior to metformin on this outcome.
- Grade CImprovedFasting insulin and HOMA insulin resistance in PCOSFasting insulin fell (SMD −1.02) and HOMA index fell (SMD −0.59) vs control; testosterone showed only a non-significant trend down. SHBG rose only in trials of at least 24 weeks.
- Grade CImprovedTestosterone, androstenedione and SHBG in PCOSCompared with placebo, free testosterone (MD −0.41), total testosterone (MD −20.39), androstenedione (MD −0.69) and BMI (MD −0.45) fell more, and SHBG rose (MD +32.06).
What the trials found for periods and hormones
The largest pooled analysis, from 2023, combined 26 randomized trials with 1,691 women with PCOS: 806 took inositol, 311 placebo and 509 metformin [1]. Regular menstrual cycles were 1.79 times as likely with inositol as with placebo (95% CI 1.13 to 2.85), and inositol was non-inferior to metformin on this outcome [1].
Hormone and weight markers moved in the same direction. Compared with placebo, free and total testosterone, androstenedione, fasting glucose and BMI fell more, and SHBG rose [1]. Each of these drew on a subset of the trials, and the BMI change was small, about half a point [1].
Insulin resistance
An earlier meta-analysis of 9 trials (247 women on inositol, 249 controls) found lower fasting insulin and HOMA insulin resistance with myo-inositol, and only a non-significant trend for testosterone [2]. SHBG rose only in trials lasting at least 24 weeks [2]. Two of its authors worked for an inositol manufacturer and another was a paid consultant to it [2].
Dose and forms studied
Most trials gave 1,000 to 4,000 mg a day of myo-inositol, 4,000 mg most often, for 7 to 24 weeks [1]. Some used D-chiro-inositol or a combination of the two forms [1]. See the inositol monograph for forms and label reading.
Limits of the evidence
The trials were mostly small and many came from Italy [1]. One early placebo-controlled trial in the pool, from 2007, was retracted in 2023 [1][4]. Cycle regularity is not the same as pregnancy or live birth, and those outcomes were not the primary endpoint [1]. That is why we grade the cycle result B rather than A [1].
Safety
A safety review found that only the highest dose studied, 12 g a day, caused mild nausea, gas and diarrhea, and severity did not rise with dose [3]. Drug interactions have not been studied systematically [3]. PCOS is a medical diagnosis, so discuss inositol with the clinician managing it, especially if you take metformin or are trying to conceive; check other medicines in the interaction checker.
Quick answers
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References
- [1]Inositol is an effective and safe treatment in polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials. Reproductive Biology and Endocrinology, 2023.
- [2]Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials. Endocrine Connections, 2017.
- [3]Inositol safety: clinical evidences. European Review for Medical and Pharmacological Sciences, 2011.
- [4]Randomized, double blind placebo-controlled trial: effects of myo-inositol on ovarian function and metabolic factors in women with PCOS (retracted 2023). European Review for Medical and Pharmacological Sciences, 2007.