Short answer: Inositol (myo-inositol and D-chiro-inositol) can improve insulin levels and some hormone results in women with PMOS, but there is little evidence that it reduces unwanted hair. A 2024 review done for the international PCOS guideline called the evidence “limited and inconclusive” and found that metformin may improve hirsutism more than inositol.[1] The guideline says inositol could be considered based on personal preference, not as a proven hair treatment.[2]
Inositol is one of the most popular supplements in the PMOS community. PMOS, short for polyendocrine metabolic ovarian syndrome, is the new name for polycystic ovary syndrome (PCOS), agreed in May 2026.[3] Many women take inositol hoping it will lower androgens (male-type hormones such as testosterone) and, in turn, reduce facial and body hair.
Below we look at what the trials measured, what they found, how inositol compares with metformin, and what to know about safety, product quality and research problems in this field. For the wider supplement picture, see our guide to supplements for hirsutism and popular hirsutism supplements versus the evidence.
What is inositol, and why is it used for PMOS?
Inositol is a sugar-like compound. The two forms studied in PMOS are myo-inositol and D-chiro-inositol, taken alone or combined, sometimes in a ratio of 40 parts myo-inositol to 1 part D-chiro-inositol.[1] Researchers have studied inositols as insulin sensitizers, meaning substances that help the body respond to insulin, and as an alternative to metformin, the standard insulin-sensitizing medicine, which often causes stomach side effects.[4]
The idea is that better insulin action means lower insulin levels, and lower insulin means less stimulation of androgen production. We explain that link in insulin resistance and facial hair.
Does inositol reduce hirsutism?
Evidence: Limited The evidence says probably not by much, and the studies are small. In a 2023 meta-analysis of 26 randomized trials with 1,691 women, only one small study (43 women) compared inositol with placebo on the Ferriman-Gallwey hair score, the standard 0 to 36 hirsutism score. It found no significant difference.[4] The same meta-analysis pooled 3 studies (220 women) comparing inositol with metformin and found that metformin lowered hair scores slightly more.[4]
The larger 2024 review by Fitz and colleagues, done for the international guideline, included 30 trials with 2,230 participants. It concluded that metformin may improve hirsutism and waist-to-hip ratio compared with inositol, and that the overall evidence for inositol in PCOS is “limited and inconclusive.”[1] A 6-month Danish trial comparing myo-inositol 4 g a day with metformin found that hair scores did not change significantly in either group.[7]
Does inositol lower testosterone and raise SHBG?
Some studies show small hormone changes, but results are inconsistent. Remember that a better blood test is not the same as less hair.
- Greff 2023 meta-analysis: Compared with placebo, inositol lowered total testosterone (by about 20 ng/dL on average), free testosterone and androstenedione, and raised SHBG, the protein that binds testosterone and keeps it inactive. The SHBG result had a very wide range of uncertainty.[4]
- Unfer 2017 meta-analysis: In 9 trials with 496 women, myo-inositol lowered fasting insulin, but the drop in testosterone was not statistically significant. SHBG rose only in studies that lasted at least 24 weeks.[5]
- Nestler 1999 trial: In 44 women with PCOS and obesity, D-chiro-inositol 1,200 mg a day for 6 to 8 weeks lowered free testosterone and more women ovulated than on placebo.[6] Hair was not measured.
Key inositol studies at a glance
This table shows what the main studies measured. Doses are reported as used in the trials, not as advice.
| Study | Type and size | Length | Inositol studied | Hair measured? | Main finding |
|---|---|---|---|---|---|
| Nestler 1999[6] | RCT, 44 women | 6-8 weeks | D-chiro-inositol 1,200 mg/day vs placebo | No | Lower free testosterone, more ovulation |
| Unfer 2017[5] | Meta-analysis, 9 RCTs, 496 women | Varied | Myo-inositol, alone or with D-chiro | Not pooled | Lower insulin; testosterone not significantly lower; SHBG up after 24+ weeks |
| Ravn 2022[7] | Open-label RCT, 45 women (28 finished) | 6 months | Myo-inositol 4 g/day vs metformin 2 g/day | Yes | No change in hair scores in either group; fewer side effects with inositol |
| Greff 2023[4] | Meta-analysis, 26 RCTs, 1,691 women | Varied | Myo- and/or D-chiro-inositol | Yes (few studies) | No hair benefit vs placebo (1 study); metformin slightly better for hair |
| Fitz 2024[1] | Guideline meta-analysis, 30 RCTs, 2,230 women | 6 weeks to 6 months | Myo 1-4 g/day; D-chiro 600 mg-1.2 g/day; combinations | Yes | “Limited and inconclusive”; metformin may be better for hirsutism |
| Minozzi 2008[8] | Uncontrolled study, 46 women | 6 months | Myo-inositol | Yes | Reported less hair; retracted in 2025 |
What doses of inositol were used in studies?
In the trials reviewed for the guideline, myo-inositol was usually given at 1 to 4 g a day, often with 200 to 400 micrograms of folic acid. D-chiro-inositol alone was given at 600 mg or 1.2 g a day, and one combination product provided 550 mg myo-inositol plus 13.8 mg D-chiro-inositol twice a day.[1]
The 2023 guideline states that no specific type, dose or combination of inositol can currently be recommended, because the evidence is too limited.[2] These numbers describe the studies, not a recommendation. Talk to your doctor before starting.
Is inositol or metformin better for hirsutism?
Metformin did slightly better for hair in direct comparisons, while inositol has fewer side effects. The 2023 International PCOS Guideline says metformin should be considered over inositol for hirsutism and central fat, noting that metformin has more stomach side effects.[2] In 4 trials, side effects occurred in 7% of women on inositol versus 53% on metformin.[4]
Neither is a strong hair treatment, though. The Endocrine Society’s 2018 guideline suggests against insulin-lowering drugs for hirsutism alone,[11] and a Cochrane review found metformin was no better than placebo for hirsutism scores.[12] For hair, the combined birth control pill is the first-line medicine, with anti-androgens added if needed.[2] See our hirsutism medication guide for details.
| Inositol | Metformin | |
|---|---|---|
| Type | Supplement | Prescription medicine |
| Effect on hair scores | No proven effect vs placebo[4] | Slightly better than inositol, but not better than placebo in a Cochrane review[4][12] |
| Stomach side effects | Uncommon[4] | Common, usually dose-related and short-lived[2] |
| Guideline view | Could be considered based on personal preference[2] | Considered over inositol for hirsutism; pill preferred over metformin for hirsutism[2] |
Is inositol safe to take?
Inositol appears to have few side effects in trials. The international guideline describes it as having limited harm,[2] and in the Greff meta-analysis, the 4 placebo-controlled studies that reported safety found no side effects with inositol.[4] Trials lasted at most 6 months, so long-term safety is unknown.[1]
Product quality is a bigger concern. The guideline notes that the regulation and quality control of inositol may differ from those of medicines.[2] In the US, the FDA does not approve dietary supplements before they are sold and does not test them before they reach consumers.[10] The guideline also encourages anyone taking inositol to tell their healthcare professional.[2]
If you are trying to get pregnant, talk to your doctor. In its section on fertility treatment, the guideline says inositol in any form “should be considered experimental therapy.”[2]
Why should you be cautious about inositol research?
Part of the inositol literature has integrity problems. The 2024 guideline review assessed 43 trials for research integrity and excluded 13 of them.[1] A widely cited 2008 study reporting that myo-inositol reduced hirsutism in 46 women had no control group and was retracted in 2025.[8] In February 2026, Retraction Watch reported that three Italian gynecology researchers had 11 retractions between them, citing duplicated data, undisclosed conflicts of interest and unreliable methods. In four retracted papers, the products studied were made by companies one of the researchers had founded, owned or directed.[9] That researcher is a co-author of the retracted 2008 study and of the 2017 meta-analysis above.[5][8]
This does not prove inositol is useless. It does mean that claims of large benefits, especially on supplement websites, deserve skepticism.
How long should you try inositol for hirsutism?
If you try it, think in months, not weeks. Inositol trials lasted from 6 weeks to 6 months,[1] and SHBG rose only in studies lasting at least 24 weeks.[5] For medicines, the Endocrine Society advises waiting at least 6 months before judging the effect on hair, because hair grows in slow cycles.[11] If you see no change after that, it is reasonable to talk to your doctor about treatments with stronger evidence, such as the birth control pill or spironolactone. Lifestyle approaches are covered in natural remedies for hirsutism.
When should you see a doctor?
See a doctor before relying on any supplement, so that the cause of your hair growth is checked. Go promptly if:
- Hair growth started suddenly or is getting worse within months
- You notice a deepening voice, an enlarged clitoris or other signs of virilization
- Your periods are irregular or have stopped
These can point to causes other than PMOS, including rare hormone-producing tumors.[11] You can score your hair growth first with our hirsutism self-check.
Frequently asked questions
Is myo-inositol or D-chiro-inositol better for hirsutism?
Neither has shown a clear benefit for hair. The 2023 guideline says no specific type, dose or combination can be recommended.[2]
Does inositol lower testosterone?
It may lower it slightly. One meta-analysis found lower total and free testosterone versus placebo,[4] while another found no significant change in testosterone.[5]
Can I take inositol with birth control or spironolactone?
We found no trials on interactions between inositol and these medicines. Tell your doctor or pharmacist about any supplement you take, as the guideline recommends.[2]
How long does inositol take to work on facial hair?
There is no good evidence that it works on facial hair at all. Hormone changes such as higher SHBG were seen only in studies lasting 24 weeks or longer.[5]
Is inositol better than metformin?
For hair, no: Metformin did slightly better in direct comparisons.[4] Inositol causes fewer stomach side effects, which is why some women prefer it.[4]
Key takeaways
- Inositol can modestly improve insulin and some hormone levels in PMOS, but trials have not shown that it reduces unwanted hair.
- The guideline review called the evidence “limited and inconclusive,” and metformin did slightly better for hair.
- No type, dose or combination of inositol is recommended by the 2023 guideline.
- Some inositol research has been retracted, so be skeptical of big claims.
- For hair, the pill, anti-androgens and hair removal have much stronger evidence.
Sources
- Fitz V, Graca S, Mahalingaiah S, et al. Inositol for Polycystic Ovary Syndrome: A Systematic Review and Meta-analysis to Inform the 2023 Update of the International Evidence-based PCOS Guidelines. J Clin Endocrinol Metab. 2024;109(6):1630-1655. PubMed 38163998
- Teede HJ, Tay CT, Laven JJE, et al. Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. J Clin Endocrinol Metab. 2023;108(10):2447-2469. PubMed 37580314
- Teede HJ, Khomami MB, Morman R, et al. Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome: a multistep global consensus process. Lancet. 2026;407(10545):2329-2339. PubMed 42119588
- Greff D, Juhász AE, Váncsa S, et al. Inositol is an effective and safe treatment in polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials. Reprod Biol Endocrinol. 2023;21(1):10. PubMed 36703143
- Unfer V, Facchinetti F, Orrù B, Giordani B, Nestler J. Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials. Endocr Connect. 2017;6(8):647-658. PubMed 29042448
- Nestler JE, Jakubowicz DJ, Reamer P, Gunn RD, Allan G. Ovulatory and metabolic effects of D-chiro-inositol in the polycystic ovary syndrome. N Engl J Med. 1999;340(17):1314-1320. PubMed 10219066
- Ravn P, Gram F, Andersen MS, Glintborg D. Myoinositol vs. Metformin in Women with Polycystic Ovary Syndrome: A Randomized Controlled Clinical Trial. Metabolites. 2022;12(12):1183. PubMed 36557221
- Minozzi M, D’Andrea G, Unfer V. Treatment of hirsutism with myo-inositol: a prospective clinical study. Reprod Biomed Online. 2008;17(4):579-582. Retracted. PubMed 18854115
- Retraction Watch. Gynecologists in Italy collect more retractions and an expression of concern. February 17, 2026. Accessed October 2026. Link
- US Food and Drug Administration. Questions and Answers on Dietary Supplements. Accessed October 2026. Link
- Martin KA, Anderson RR, Chang RJ, et al. Evaluation and Treatment of Hirsutism in Premenopausal Women: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(4):1233-1257. PubMed 29522147
- van Zuuren EJ, Fedorowicz Z, Carter B, Pandis N. Interventions for hirsutism (excluding laser and photoepilation therapy alone). Cochrane Database Syst Rev. 2015;(4):CD010334. PubMed 25918921
This article is for education and is not medical advice. Talk to a doctor about diagnosis and treatment.