Inositol

non-nutrient/non-botanical

Take with food

What is it

Inositol is a sugar alcohol (cyclitol) once classified as part of the vitamin B complex. It exists in nine stereoisomers; myo-inositol is by far the most abundant in the body and the most commonly supplemented form. It is found in foods including beans, grains, fruits, and nuts.

How it works

Inositol is a key component of cell membrane phospholipids (phosphatidylinositol) and serves as a precursor to second messengers (inositol phosphates) that mediate cellular responses to many hormones and neurotransmitters. It plays particularly important roles in insulin signaling, neurotransmitter signaling, and cell function in the ovaries and brain. Myo-inositol and D-chiro-inositol are the two clinically relevant forms. Myo-inositol acts as a second messenger in the FSH (follicle-stimulating hormone) pathway and supports oocyte maturation. D-chiro-inositol is more involved in androgen synthesis and glucose metabolism. The natural ratio of myo to D-chiro inositol in tissues is approximately 40:1, and many therapeutic formulations match this ratio. In polycystic ovary syndrome (PCOS), insulin resistance disrupts inositol metabolism and shifts the myo:D-chiro ratio. Supplementation with myo-inositol (often combined with D-chiro at the 40:1 ratio) has been shown to improve insulin sensitivity, menstrual regularity, and ovulation in many women with PCOS.

Evidence for 6 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Polycystic ovary syndrome (PCOS)

Grade B

Good evidence

Multiple clinical trials and meta-analyses suggest myo-inositol (often with D-chiro at 40:1 ratio) improves insulin sensitivity, restores menstrual regularity, supports ovulation, and may improve fertility outcomes in women with PCOS. Effects develop over 2 to 6 months.

Gestational diabetes prevention

Grade B

Good evidence

Several trials in high-risk women suggest myo-inositol supplementation during pregnancy may reduce gestational diabetes incidence. Best evidence in women with PCOS or family history of diabetes.

Insulin sensitivity / metabolic syndrome

Grade C

Moderate evidence

Some research suggests inositol may improve insulin sensitivity and metabolic markers in people with insulin resistance, beyond PCOS contexts. Evidence is moderate.

Panic disorder / anxiety

Grade C

Moderate evidence

Older clinical trials suggested high-dose inositol (12 to 18 g per day) may reduce panic attacks. Effects may be comparable to fluvoxamine in some studies. Replication is limited.

Depression

Grade D

Mixed evidence

Some studies suggested possible antidepressant effects of high-dose inositol, but evidence is inconsistent. Not recommended as a primary treatment for depression.

OCD

Grade D

Mixed evidence

Small trials suggested possible benefits in OCD at high doses. Replication is limited.

5 commercial forms

Myo-inositol

The dominant inositol form in the body; well absorbed.

Most common supplement form. Used as monotherapy in many PCOS studies.

D-chiro-inositol

Specific isomer involved in insulin and androgen signaling.

Used at lower doses (50 mg twice daily) often combined with myo-inositol.

Myo + D-chiro 40:1 combination

Matches natural physiological ratio.

Most clinically studied PCOS formulation. Provides both isomers at physiological ratio.

Inositol hexaphosphate (IP6, phytic acid)

Plant-based form found in seeds and grains.

Distinct from free inositol; marketed for different uses (antioxidant, mineral chelation).

Inositol powder

Dissolves easily in water; mildly sweet taste.

Cost-effective for high doses. Practical for PCOS protocols.

Dosage

Typical doses are 2 to 4 g of myo-inositol twice daily (total 4 to 8 g per day). For PCOS, 2,000 mg twice daily is the most common regimen. The 40:1 myo:D-chiro combination provides 2,000 mg myo + 50 mg D-chiro twice daily. For depression and anxiety, higher doses (12 to 18 g per day) have been used. There is no established Tolerable Upper Intake Level.

When and how to take it

WHEN: For PCOS, take divided doses (typically morning and evening). Can be taken with or without food. HOW: Inositol powder dissolves easily in water and has a mildly sweet taste. Capsules are convenient but may require multiple per dose for therapeutic amounts. Allow 2 to 3 months of consistent use to evaluate effects on PCOS-related outcomes.

Food sources

Food	Amount	%DV
Cantaloupe	1 cup	—
Citrus fruits (oranges, grapefruit)	1 medium	—
Beans and lentils	1/2 cup cooked	—
Whole grains	1 cup cooked	—
Brown rice	1 cup cooked	—
Nuts (almonds, walnuts)	1 oz	—
Bran cereals	1 cup	—

Safety

Inositol is generally very well tolerated, even at high doses. Side effects are typically mild and include nausea, gas, bloating, and diarrhea at high doses (above 12 g per day). There is no established Tolerable Upper Intake Level. Long-term safety appears acceptable in available research.

Who should be cautious

Pregnant women with PCOS may use myo-inositol under medical guidance; some research suggests benefits for gestational diabetes prevention. People with diabetes should monitor blood glucose. Those on lithium should consult a psychiatrist. People with bipolar disorder should use caution; high-dose inositol has been studied for depression but could theoretically affect mood stability.

Interactions

Inositol may potentiate the effects of insulin and oral diabetes medications, potentially increasing hypoglycemia risk in people with diabetes. May affect lithium levels (used in bipolar disorder); inositol could theoretically reduce lithium's effectiveness. Otherwise, few significant drug interactions are documented.

Frequently asked questions

Which inositol form should I take for PCOS?⌄

The 40:1 myo:D-chiro combination (2,000 mg myo + 50 mg D-chiro, twice daily) has the strongest evidence. Myo-inositol alone at 2 g twice daily is also widely used and supported by research.

How long until I see PCOS effects?⌄

Improvements in menstrual regularity, ovulation, and metabolic markers typically develop over 2 to 6 months of consistent daily use. Be patient with the protocol.

Is inositol the same as vitamin B8?⌄

Inositol was historically classified as part of the B-vitamin complex (sometimes called vitamin B8), but it is no longer considered a true vitamin since the body can synthesize it. The classification is outdated.

Can men take inositol?⌄

Yes. While inositol is best known for PCOS, it may also support insulin sensitivity, metabolic health, and mood in men. It is generally well tolerated.

Is inositol safe in pregnancy?⌄

Yes, and it may have specific benefits. Some research suggests myo-inositol during pregnancy may reduce gestational diabetes risk in high-risk women. Consult an obstetrician about supplementation during pregnancy.

References

Wikidata: Inositol — Wikidata link
PubChem: Inositol (CID 892) — PubChem link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.