Supplement
Myo-Inositol
Vitamin · inositol (marketed as vitamin B8, but not a vitamin in the strict sense)
Myo-inositol is a sugar-like substance that the body makes itself and that relays signals in every cell, including the insulin signal. As a supplement, it has one clear strength: in polycystic ovary syndrome (PCOS) it is well studied and improves the cycle and metabolic values. For anxiety, mood and fertility, the picture is considerably thinner.
In short
In women with PCOS, myo-inositol normalizes the menstrual cycle more often than placebo according to a meta-analysis of 26 randomized studies, slightly improves blood glucose, insulin and androgens, and is considerably better tolerated than metformin. The 2023 international PCOS guideline therefore considers inositol an option but sees the clinical benefit as limited and does not recommend any particular form, dose or mixture. In pregnancy, myo-inositol lowered the risk of gestational diabetes in a Cochrane review, with low certainty of evidence. For anxiety and depression, the meta-analysis shows no established effect, and the often-advertised 40:1 ratio comes from mouse experiments.
What it is
Inositol is a ring-shaped molecule with six carbon atoms, chemically related to a sugar. The most important form in the body is myo-inositol. The body makes it itself from glucose, which is why, despite the marketing name vitamin B8, it is not a vitamin in the strict sense. It also comes from food, from grains, corn, legumes and meat.
Under the influence of insulin, myo-inositol gives rise to D-chiro-inositol, a second form with its own role in sugar metabolism. Products contain either only myo-inositol, only D-chiro-inositol or a mixture. In the specialist literature, myo-inositol is classified as an insulin-sensitizing substance and is frequently used in PCOS, although for a long time comparatively little was collected systematically about its safety.
How it is supposed to work
Myo-inositol is a building block of messenger substances that relay the insulin signal inside the cell. Insulin resistance is often involved in PCOS, and an excess of insulin drives the production of male hormones in the ovaries. The idea: more inositol improves insulin action, so insulin and androgens fall, and the cycle can normalize.
In addition, there is an observation from the ovaries themselves. In women without PCOS, the ratio of myo- to D-chiro-inositol there is 100:1; in PCOS it is 0.2:1. From this came the recommendation to give both forms in a 40:1 ratio. So far, this ratio has only been supported in mouse models.
In the brain, inositol is part of the phosphatidylinositol signaling pathway, which also plays a role in the action of some psychiatric drugs. Lithium lowers the inositol level in the frontal brain, valproate slows inositol production. From this derives the hope that inositol could help with anxiety and depression.
What is well supported
In PCOS, myo-inositol is one of the well-studied supplements. A meta-analysis of 26 randomized studies with 1,691 patients found a 1.79-fold higher chance of a regular cycle compared with placebo and small but significant improvements in body mass index, fasting glucose, insulin, testosterone and SHBG. Compared with metformin, there was no clear difference in the cycle; that is not proof of equivalence, and the meta-analysis for the guideline sees metformin ahead for hirsutism and waist-to-hip ratio. Inositol was considerably better tolerated: in 4 comparative studies, side effects occurred in 7 percent compared with 53 percent under metformin. The studies used between 1,000 and 4,000 mg of myo-inositol daily, most often 4,000 mg, over 12 to 24 weeks. This is a figure from the studies, not an intake recommendation.
There are also human data outside PCOS. A Cochrane review of 7 randomized studies with 1,319 pregnant women found less gestational diabetes under myo-inositol (risk ratio 0.53), fewer hypertensive disorders of pregnancy and fewer preterm births. In people with metabolic disorders, inositol lowered triglycerides as well as total and LDL cholesterol in a meta-analysis of 14 studies. For panic disorder, there are two small double-blind studies with positive results, one of them with an effect comparable to that of the antidepressant fluvoxamine.
What the studies show
Meta-analysis Greff 2023, PCOS
26 randomized studies with 1,691 women, inositol versus placebo or metformin. The primary endpoint was normalization of the cycle: risk ratio 1.79 versus placebo, no clear difference versus metformin. Metabolic and hormone values improved slightly. Side effects 7 versus 53 percent in the comparison with metformin.
Guideline meta-analysis Fitz 2024
30 studies with 2,230 participants, prepared for the international PCOS guideline. Benefit for some metabolic values, possible advantages of D-chiro-inositol for ovulation, no effect on other endpoints. Metformin performed better for hirsutism and waist-to-hip ratio, inositol for tolerability. The authors’ conclusion: the evidence is limited and inconclusive.
Cochrane 2023, gestational diabetes
7 randomized studies with 1,319 pregnant women, 6 of them from Italy. Gestational diabetes risk ratio 0.53 from 6 studies with 1,140 women, plus less hypertension and fewer preterm births. The authors rate the certainty of evidence as low to very low and consider the approach promising but not established.
Cochrane 2018, fertility in PCOS
13 randomized studies with 1,472 women, mostly myo-inositol as pretreatment before in vitro fertilization. The evidence was of low to very low quality, mainly because of poorly reported methods and missing data on live births. Whether inositol increases the birth rate remained uncertain: the odds ratio was 2.42, but the confidence interval ranged from 0.75 to 7.83.
Panic disorder 1995 and 2001
Two double-blind crossover studies with 21 and 20 patients, each over about one month. Under inositol, frequency and severity of panic attacks fell more than under placebo; compared with fluvoxamine, attacks decreased by 4.0 versus 2.4 per week in the first month. The studies used very high amounts of 12 and up to 18 grams daily.
Where the data stop
Even in PCOS, the effects are smaller than advertising suggests. The 2023 international guideline rates the evidence as very low, sees only limited clinical benefit for ovulation, hirsutism and weight, and recommends metformin for hirsutism and abdominal fat. It explicitly cannot recommend any particular form, dose or mixture, including the advertised 40:1 ratio. For fertility, the guideline considers inositol experimental; a Cochrane review found only low- to very-low-quality evidence on this and no established effect on live births.
For anxiety and depression, a meta-analysis of 7 studies on depression and 4 on anxiety disorders found no significant effect, only trends, for example in premenstrual low mood. The positive panic studies are small, short and used amounts far above those in the PCOS studies. We did not find studies showing an improvement in hormones or cycle in metabolically healthy women without PCOS. We did not find verifiable experience reports that go beyond the studies.
Status, approval and legal
In Germany, myo-inositol is sold as a food supplement. The international PCOS guideline points out that different rules and quality controls apply to such products than to medicines and that dose and quality can vary. It encourages women who take inositol to tell their doctor. We did not find an official upper limit from EFSA, BfR or NIH. Relevance for doping is not noted in the sources reviewed.
Safety
Myo-inositol is considered well tolerated. No side effects were reported in placebo-controlled PCOS studies, and according to a review, only the highest amount studied, 12 grams daily, caused mild nausea, flatulence or diarrhea. In pregnancy, no harm was described in 7 studies; however, long-term consequences for the children have not been studied, and the Cochrane authors call for better recording of possible side effects. Because inositol slightly lowers blood glucose, you should coordinate its use with diabetes medication with your doctor. Lithium and valproate interfere with inositol metabolism in the brain; anyone taking these medicines should only use inositol after consultation.
BK-Score Supported, with caveats
| Human evidence | 7 | |
|---|---|---|
| Mechanism | 7 | |
| Safety data | 7 | |
| Hype gap | 5 | |
| Track record of use | 7 |
Well studied for PCOS, with limited clinical benefit. A meta-analysis of 26 RCTs with 1,691 patients (Reprod Biol Endocrinol 2023) shows a regular cycle more often than with placebo (RR 1.79; 95 % CI 1.13–2.85) and improvements in BMI, testosterone, fasting glucose and insulin; in direct comparison with metformin, no clear difference in the cycle, with fewer side effects (7 instead of 53 percent in 4 studies); that is not formal non-inferiority, and according to the guideline meta-analysis, metformin works better for hirsutism and waist-to-hip ratio. The meta-analysis for the international PCOS guideline (30 studies, 2,230 participants, J Clin Endocrinol Metab 2024) calls the evidence limited and inconclusive; the 2023 guideline recommends no particular form, dose or combination – the 40:1 ratio rests on mouse models – and classifies inositol for fertility as experimental. A Cochrane review (7 RCTs, 1,319 pregnant women) finds less gestational diabetes (RR 0.53) with low certainty of evidence. For depression and anxiety disorders, a meta-analysis (7 and 4 RCTs respectively) shows no significant effect; the panic data come from 2 small crossover studies. The insulin signaling pathway as a second messenger is established in humans. The broad marketing to metabolically healthy women and against anxiety is not covered by this evidence.
The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)
Frequently asked questions about myo-inositol
Does inositol help with PCOS?
Yes, to a moderate degree. A meta-analysis of 26 studies shows a regular cycle more often and slightly better metabolic and hormone values. The international guideline considers it an option but sees the clinical benefit as limited.
Is myo-inositol better than metformin?
For the cycle, the meta-analysis found no clear difference, but that does not establish equivalence; the guideline calls the evidence limited. It was considerably better tolerated: side effects occurred in 7 instead of 53 percent. Metformin had a stronger effect on hirsutism and abdominal fat. The decision belongs in a gynecology or endocrinology practice.
What does the 40 to 1 ratio do?
The rationale comes from mouse experiments. The 2023 international PCOS guideline explicitly does not recommend any particular form, dose or mixture, because good comparative studies are lacking.
Does inositol help with anxiety and panic attacks?
Two small studies in panic disorder were positive, though with very high amounts. A meta-analysis across all anxiety disorders found no significant effect. For anxiety disorders, medical or psychotherapeutic treatment is the right path.
Can inositol help when trying to conceive?
The guideline classifies inositol for fertility as experimental; a Cochrane review found only very low-quality evidence. Whether it increases the number of births is open.
Is inositol a vitamin?
No, even though it is often marketed as vitamin B8. The body makes myo-inositol itself from glucose; it is also found in grains, legumes and meat.
Related
- Works together withMagnesium
- Works together withVitamin B complex
- Same categoryVitamin D3
- Same categoryMethylfolate
- Same categoryVitamin K2 (MK-7)
- Also for hormonesZinc
- Same goal: fat burning / weight lossBerberine
- Same goal: hormone balanceChasteberry (Vitex agnus-castus)
- Same goal: improving moodOral lavender oil (Silexan)
- Same goal: hormone balanceBlack cohosh (Cimicifuga)
- Same goal: hormone balanceTribulus terrestris
- Same goal: improving moodMaca
- QuestionCravings and blood sugar fluctuations (German)
Sources
- Greff et al., Reprod Biol Endocrinol 2023
- Fitz et al., J Clin Endocrinol Metab 2024
- Teede et al., International PCOS guideline 2023, J Clin Endocrinol Metab
- Motuhifonua et al., Cochrane Database Syst Rev 2023 (CD011507)
- Showell et al., Cochrane Database Syst Rev 2018 (CD012378)
- Mukai et al., Hum Psychopharmacol 2014
- Benjamin et al., Am J Psychiatry 1995
- Palatnik et al., J Clin Psychopharmacol 2001
- Tabrizi et al., Lipids Health Dis 2018
- Carlomagno and Unfer, Eur Rev Med Pharmacol Sci 2011
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-10-04.