What is Vitamin B8 (Myo-Inositol)?

Myo-inositol is a naturally occurring sugar alcohol found in the body and many foods. It is sometimes called vitamin B8, but it is not considered an essential vitamin.

What is myo-inositol used for?

It is commonly used to support insulin sensitivity and hormone balance, especially in people with PCOS. It is also used in fertility support and for certain mental health symptoms, though evidence varies by condition.

How much myo-inositol should I take?

Common supplemental amounts are 2–4 g per day. Dosing can vary by goal and product, so follow label directions and clinician guidance.

Does myo-inositol help with fertility?

It may support ovulation and menstrual regularity in PCOS and is also used to support egg quality in some fertility settings. Some evidence also suggests potential benefits for sperm parameters in men.

Is myo-inositol safe, and who should be cautious?

It is generally well tolerated, but some people may experience mild gastrointestinal side effects. People who are pregnant, breastfeeding, or taking medications for blood sugar or mental health should consult a clinician before use.

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Vitamin B8 (Myo-
Inositol)

Moderate study situation·7/10

A higher score indicates better study conditions, but not necessarily effectiveness.

A naturally occurring nutrient often used as a supplement for metabolic, reproductive, and mental health.

PCOS Male Fertility Depression / Mood Enhancement Glucose Metabolism Anxiety Relief Female Fertility Hormone Balance Weight Management

dose range

2–4 g

Divide daily dose into two (e.g., 2 g morning, 2 g evening) for better tolerability.

Consumption

Take with or without meals; mix powdered form in water or juice. For PCOS and metabolic benefits, 2–4 g/day. Higher doses (12–18 g/day) used for psychiatric conditions only under supervision.

Not fat-soluble.

Best time

Two divided doses with first and second meals for metabolic/fertility benefits. High-dose protocols require professional guidance.

Description

Myo-inositol (formerly vitamin B8) is a sugar alcohol found abundantly in the human body and many foods. It plays a vital role in cell signaling, insulin sensitivity, and hormone balance. It is not an essential vitamin but is regularly used as a supplement, especially for PCOS, fertility, and some mental health conditions.

benefits

Main effects with level of evidence

Moderate

Note on evidence

Strong evidence supports use in PCOS and insulin resistance. Evidence for mental health benefits is mixed but promising in some studies.

Improves Symptoms of Polycystic Ovary Syndrome (PCOS)

Strong

Myo-inositol supplementation improves insulin sensitivity, restores ovulation, and regulates menstrual cycles in women with PCOS.

Particularly relevant for: Women with PCOS

S3 · PMC8896029: Myo-Inositol in PCOS Management S4 · Cochrane Review: Inositol for PCOS

Supports Female Fertility and Egg Quality

Moderate

May improve oocyte quality and increase pregnancy rates, including in women undergoing IVF.

Particularly relevant for: Women seeking fertility assistance

S4 · Cochrane Review: Inositol for PCOS S5 · PubMed: Myo-Inositol Safety and Efficacy

May Improve Sperm Quality in Men

Limited

Some studies suggest benefits for sperm motility and count, potentially aiding male fertility.

Particularly relevant for: Men seeking fertility support

S2 · Examine.com: Inositol

Supports Blood Sugar Control and Insulin Sensitivity

Moderate

Helps reduce fasting insulin and blood sugar in individuals with metabolic syndrome or insulin resistance.

Particularly relevant for: Individuals with insulin resistance or metabolic syndrome

S2 · Examine.com: Inositol S3 · PMC8896029: Myo-Inositol in PCOS Management

Potential Mental Health Benefits

Mixed

High-dose myo-inositol may help reduce symptoms of anxiety, depression, and OCD, though evidence is mixed and more research is needed.

Particularly relevant for: Individuals with anxiety, depression, or OCD

S2 · Examine.com: Inositol S5 · PubMed: Myo-Inositol Safety and Efficacy

Safety & Information

Important safety information & known risks

For educational purposes only • not medical advice

Well tolerated at recommended doses; main risk is gastrointestinal upset at higher intake.

warning notices

GI side effects (nausea, diarrhea) possible above 12 g/day.
Long-term safety considered good, but research on use in pregnancy and breastfeeding is lacking.
Rare allergic reactions reported.
Avoid doses above 12 g/day unless supervised by a healthcare professional due to risk of GI side effects.
Use only with clinician oversight if taking diabetes medication (may affect blood sugar).
Do not use in pregnancy or breastfeeding unless directed by a qualified provider; research on safety is insufficient.
People with bipolar disorder should consult a psychiatrist before use, as inositol may impact mood stability.

Known interactions with medications

May potentiate effects of antidiabetic medication; monitor hypoglycemia risk.
May interact with mood stabilizers in psychiatric conditions.

Contraindications / special precautions

High-dose use in people with bipolar disorder without professional oversight.
Use in pregnancy or breastfeeding unless directed by a qualified professional.

interactions

Important interactions between active ingredient ↔ supplement / medication / food

Myo-inositol may interact with blood sugar–lowering medications and other psychiatric medications.

May enhance hypoglycemic effect of diabetes drugs.

drug · Diabetes medication

MonitorModerate

Why

Myo-inositol improves insulin sensitivity and may lower blood glucose, increasing effect of antidiabetic medications.

recommendation

Monitor blood glucose closely and consult healthcare provider to adjust medication if needed.

S1 · NIH Office of Dietary Supplements: Inositol Fact Sheet S6 · WebMD: Inositol Overview

May alter the effects of mood-stabilizing psychiatric drugs.

drug · Mood stabilizers

CautionLimited

Why

High-dose inositol may influence neurotransmitter pathways; risk for people with bipolar disorder.

recommendation

Discuss use with psychiatrist before combining with psychiatric medications.

S2 · Examine.com: Inositol S5 · PubMed: Myo-Inositol Safety and Efficacy

mechanisms of action

Brief explanations of how it works

Enhances Insulin Signaling and Sensitivity

Acts as a second messenger for insulin, supporting glucose uptake and signaling in cells. This underlies its benefits for PCOS and blood sugar regulation.

S3 · PMC8896029: Myo-Inositol in PCOS Management S2 · Examine.com: Inositol