Inositol
Summary
In women with PCOS, inositol (mostly 1,000–4,000 mg/day of myo-inositol) made regular periods more likely than placebo and lowered insulin and testosterone in a 2023 meta-analysis of 26 trials (grade B). In pregnancy, myo-inositol may lower gestational diabetes risk, but a 2023 Cochrane review rated that evidence low certainty (grade C).
Key facts
- A carbocyclic sugar made in the body and found in cereals, corn, legumes and meat; myo-inositol and D-chiro-inositol are the two forms studied[1][3]
- PCOS: more regular periods vs placebo (B); lower insulin and androgens (C). Pregnancy: lower gestational diabetes incidence (C)[1][2][3]
- 1,000–4,000 mg/day of myo-inositol in PCOS trials (4,000 mg most often); 2,000 mg twice daily in a pregnancy trial[1][5]
- None set; inositol is not an essential nutrient[3]
- None reported in our sources; not systematically studied[6]
- Mild nausea, gas and diarrhea, reported only at 12 g/day[6]
- 5 graded human outcomes on this page
- October 10, 2026
How it works
ProposedMyo-inositol is one of the messengers that carries the insulin signal inside cells, and levels track insulin sensitivity. Improving that signal is the proposed reason it could help the insulin resistance seen in PCOS and pregnancy.[1][3]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| PCOS | Grade B | Improved | Meta-analysis of 26 trials · n = 1,691 · 2023 | 3 rows |
| Pregnancy | Grade C | Improved | Systematic review of 7 trials · n = 1,319 · 2023 | 2 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Regular menstrual periods in PCOS | Improved | Grade B | Meta-analysis · n = 1,691 · 2023 Women with PCOS in 26 RCTs (806 inositol, 311 placebo, 509 metformin) Form: myo-inositol, D-chiro-inositol or both · Dose: Mostly 1,000–4,000 mg/day myo-inositol (4,000 mg most often); D-chiro-inositol 600–1,200 mg/day in two trials · Duration: 7–24 weeks Regular 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. | 36703143 (opens PubMed)Source [1] |
| Testosterone, androstenedione and SHBG in PCOS | Improved | Grade C | Meta-analysis · n = 1,691 · 2023 Women with PCOS in 26 RCTs Form: myo-inositol, D-chiro-inositol or both · Dose: Mostly 1,000–4,000 mg/day myo-inositol · Duration: 7–24 weeks Compared 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). | 36703143 (opens PubMed)Source [1] |
| Gestational diabetes incidence | Improved | Grade C | Systematic review · n = 1,319 · 2023 Pregnant women enrolled at 10–24 weeks in 7 RCTs (6 in Italy, 1 in Ireland) Form: myo-inositol, alone or in combination products · Dose: Varied across trials · Duration: From enrolment to the glucose test or delivery Gestational diabetes was less frequent with myo-inositol (RR 0.53, 95% CI 0.31–0.90; 6 studies, 1,140 women), rated low-certainty evidence. Hypertensive disorders (RR 0.34) and preterm birth (RR 0.35) were also lower. | 36790138 (opens PubMed)Source [3] |
| Fasting insulin and HOMA insulin resistance in PCOS | Improved | Grade C | Meta-analysis · n = 496 · 2017 Women with PCOS in 9 RCTs (247 treated, 249 controls) Form: myo-inositol alone or with D-chiro-inositol · Dose: Varied across trials, up to 4,000 mg/day myo-inositol · Duration: 12–24 weeks or longer Fasting 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. | 29042448 (opens PubMed)Source [2] |
| Gestational diabetes in women with a parent with type 2 diabetes | Improved | Grade C | RCT · n = 220 · 2013 Pregnant women in Italy with a parent with type 2 diabetes Form: myo-inositol powder with folic acid · Dose: 2,000 mg myo-inositol plus 200 mcg folic acid twice daily (4,000 mg/day); control got folic acid only · Duration: End of first trimester to delivery Gestational diabetes occurred in 6% vs 15.3% (P = 0.04; odds ratio 0.35); fetal macrosomia was also less frequent. Other outcomes did not differ. | 23340885 (opens PubMed)Source [5] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Myo-inositol (powder or capsules) | Varies[1] | No human absorption data in our sources.[1] | Mild stomach upset reported only at 12 g/day.[6] | PCOS and pregnancy trials (1,000–4,000 mg/day) |
| Myo-inositol plus D-chiro-inositol (about 40:1, e.g. 1,100 mg + 27.6 mg) | Varies[1] | No human absorption data in our sources.[1] | No specific tolerance data in our sources.[1] | PCOS trials, 24 weeks |
| D-chiro-inositol alone | Varies[1] | No human absorption data in our sources.[1] | No specific tolerance data in our sources.[1] | Two short PCOS trials (600–1,200 mg/day, 7 weeks) |
Studied doses
Doses studied in human trials ranged from 1,000 to 4,000 mg/day of myo-inositol, most often 4,000 mg/day, for 12 to 24 weeks in PCOS trials. A pregnancy trial used 2,000 mg twice daily from the end of the first trimester to delivery. Tolerance data extend to 12 g/day.[1][5][6]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
None found in our sources.
Who should be careful
- Pregnancy
- Myo-inositol has been tested in pregnant women, but the trials were small and mostly from Italy, and harms were poorly reported. Pregnancy use belongs in a plan with the obstetric team.[3]
- PCOS medicines
- Inositol was non-inferior to metformin for regular periods in pooled trials, but that does not make it a swap for prescribed treatment without the prescriber.[1]
- High doses
- Only the highest studied dose, 12 g/day, caused mild nausea, gas and diarrhea.[6]
- Medicines
- No drug interactions are reported in our sources, but they have not been systematically studied.[6]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Safety and evidence quality
Inositol was well tolerated in trials; the bigger question is the quality of the evidence.
- Side effects
- A safety review found that only 12 g/day caused mild gastrointestinal effects, and their severity did not rise with dose.[6]
- Retracted trial
- A 2007 PCOS trial of 4 g/day myo-inositol (Gerli) was retracted in 2023; both PCOS meta-analyses on this page included it.[1][2][7]
- Industry ties
- Two authors of the 2017 PCOS meta-analysis worked for an inositol manufacturer.[2]
How to read the label
- Label dose vs clinical dosePCOS trials most often used 4,000 mg/day of myo-inositol and the pregnancy trial 2,000 mg twice daily. Compare the myo-inositol listed per serving with those totals.[1][5]
- Check which inositolA label should name myo-inositol, D-chiro-inositol or both, with amounts. "Inositol" alone cannot be matched to a trial dose.[1]
- Combination ratiosThe combination trials used about 40 parts myo-inositol to 1 part D-chiro-inositol (1,100 mg + 27.6 mg).[1]
Cost per studied dose, without the sales pitch
Compare any product you already have by the amount it delivers, not by capsule count or front-of-pack weight.
Cost per studied dose
Enter the price, servings and the amount per serving from your label.
Frequently asked questions
Does inositol help PCOS?
Pooled trials suggest it helps. A 2023 meta-analysis of 26 trials found regular periods 1.79 times as likely as with placebo, plus lower testosterone and insulin. The trials were small, and one was later retracted.[1][7]
How much inositol was used in PCOS studies?
Most trials used 1,000–4,000 mg/day of myo-inositol for 12–24 weeks, with 4,000 mg/day the most common dose.[1]
Does myo-inositol lower gestational diabetes risk?
Possibly. A 2023 Cochrane review found about half the risk (RR 0.53) but rated the evidence low certainty. A 2022 meta-analysis of 7 trials reached a similar result (OR 0.32) and advised caution because of heterogeneity.[3][4]
What dose was used in pregnancy?
The main Italian trial gave 2,000 mg myo-inositol with folic acid twice daily from the end of the first trimester.[5]
Is inositol safe?
It was well tolerated in trials. A safety review found that only 12 g/day caused mild nausea, gas or diarrhea.[6]
Myo-inositol or D-chiro-inositol?
Most trials used myo-inositol. Some used a roughly 40:1 myo- to D-chiro-inositol mix; D-chiro-inositol alone was tested in only two short trials.[1]
Sources
- [1]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. meta-analysis
- [2]Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials.. Endocr Connect, 2017. meta-analysis
- [3]Antenatal dietary supplementation with myo-inositol for preventing gestational diabetes.. Cochrane Database Syst Rev, 2023. systematic-review
- [4]Myo-inositol supplementation for the prevention of gestational diabetes: A meta-analysis of randomized controlled trials.. Eur J Obstet Gynecol Reprod Biol, 2022. meta-analysis
- [5]myo-Inositol supplementation and onset of gestational diabetes mellitus in pregnant women with a family history of type 2 diabetes: a prospective, randomized, placebo-controlled study.. Diabetes Care, 2013. RCT
- [6]Inositol safety: clinical evidences.. Eur Rev Med Pharmacol Sci, 2011. review
- [7]Randomized, double blind placebo-controlled trial: effects of myo-inositol on ovarian function and metabolic factors in women with PCOS.. Eur Rev Med Pharmacol Sci, 2007. RCT
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every row re-read against its abstract and the included-study tables (PMC9878965, PMC5655679). Found that the 4 g/day PCOS trial in the brief (PMID 18074942) was retracted in 2023; it is cited only as a retraction, never as evidence. Manufacturer ties disclosed for the 2017 meta-analysis; the pregnancy trial labelled open-label. Page set indexable.