Myo-inositol

Inositol stereoisomer, supplement. Has evidence base in polycystic ovary syndrome (PCOS)

ATC code: A11JA-MYO-INOSITOL (Myo-inositol)

Brand names – supplements

Inofolic, Now Myo-Inositol, Jarrow Myo-Inositol, Thorne Myo-Inositol

Supplements are not tested in clinical trials and are not registered as medications.

Mechanism of action

Myo-inositol is one of 9 inositol stereoisomers (cyclohexane-1,2,3,4,5,6-hexaol), related to glucose. In the cell myo-inositol is a phosphoinositide component and second messenger inositol-1,4,5-trisphosphate (IP3) regulating intracellular calcium and insulin signalling. In polycystic ovary syndrome (PCOS) patients have reduced epimerase activity converting myo-inositol to D-chiro-inositol in ovaries; myo-inositol supplementation restores insulin sensitivity and normalises ovulation. Oral bioavailability is high, peak in 2-4 hours, renal and metabolic excretion. 2023 PCOS guideline classifies inositols as experimental therapy with possible effect requiring further studies.

Indications

Polycystic ovary syndrome

Adjunct

Myo-inositol is the only supplement with relatively convincing evidence in polycystic ovary syndrome (PCOS). Pundir 2018 (BJOG) meta-analysis of 13 RCTs in 1472 patients: myo-inositol 4 g/day × 3-6 months restores ovulation in 70% of PCOS patients vs 33% on placebo, reduces LH and testosterone and improves insulin sensitivity. 2023 PCOS guideline classifies inositols as experimental therapy with possible effect for irregular cycles and insulin resistance in PCOS, requiring further RCTs; conditional recommendation. SEGO 2017 (Spanish PCOS consensus) lists hormonal contraceptives or metformin first-line for anovulation; myo-inositol is additional option. If pregnancy planned – optimal combination is myo-inositol + folic acid under gynaecology supervision.

Sources

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Type 2 diabetes mellitus

Not recommended

Myo-inositol is sold for «natural blood sugar control» on the insulin signalling improvement hypothesis. Evidence in confirmed T2DM is weak: no quality RCTs with , cardiovascular event or microvascular complication endpoints. Standards of Care 2024 for T2DM lists metformin first-line, then SGLT2i and GLP-1 RA per cardiovascular and renal risk; myo-inositol is in no international diabetes guideline. In PCOS patients with insulin resistance the effect is described above; in patients with confirmed T2DM without PCOS replacing standard therapy with myo-inositol is not justified. If myo-inositol was recommended for T2DM instead of metformin, consider seeking a second opinion from an endocrinologist.

Sources

BJOG: Inositol treatment of anovulation in women with polycystic ovary syndrome: meta-analysis of randomised trials (2018)

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Official sources

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AEMPS / CIMA

Spanish Medicines Information Centre (CIMA)

Label dated: 09/17/2015

Safety

Contraindications

Known hypersensitivity
Bipolar disorder (myo-inositol theoretically modulates second messenger and may alter lithium effect)

Serious adverse effects

Allergic reactions (rare)

Common adverse effects

Nausea
Flatulence
Diarrhoea (at >4 g/day doses)
Headache

PregnancyFDA N

Myo-inositol combined with folic acid is used in PCOS patients during pregnancy planning and in the first trimester. Inofolic Combi and Ovusitol are registered in Spain. Doses of 2-4 g/day are considered safe in standard RCTs. In pregnant women without PCOS supplementation is not needed.

Breastfeeding

Myo-inositol is in breast milk at physiological concentrations. In lactating women supplement doses are considered safe. Inofolic as a pharmaceutical preparation in lactation under medical supervision.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Myo-inositol used for?

Myo-inositol is evaluated for the following indications with varying evidence strength: Polycystic ovary syndrome (evidence tier C), Type 2 diabetes mellitus (evidence tier D). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Myo-inositol?

Common side effects of Myo-inositol (≥ 1 in 100): Nausea, Flatulence, Diarrhoea (at >4 g/day doses), Headache. See the Safety section for uncommon and serious reactions.

Is Myo-inositol safe during pregnancy?

FDA category N. Myo-inositol combined with folic acid is used in PCOS patients during pregnancy planning and in the first trimester. Inofolic Combi and Ovusitol are registered in Spain. Doses of 2-4 g/day are considered safe in standard RCTs. In pregnant women without PCOS supplementation is not needed.

Is Myo-inositol compatible with breastfeeding?

Who should not take Myo-inositol?

Myo-inositol is contraindicated in: Known hypersensitivity; Bipolar disorder (myo-inositol theoretically modulates second messenger and may alter lithium effect). Full list in the Safety section.

Mechanism of action

Indications

Polycystic ovary syndrome

Adjunct

Sources

Safety

Contraindications

Known hypersensitivity
Bipolar disorder (myo-inositol theoretically modulates second messenger and may alter lithium effect)

Serious adverse effects

Allergic reactions (rare)

Common adverse effects

Nausea
Flatulence
Diarrhoea (at >4 g/day doses)
Headache

PregnancyFDA N

Breastfeeding

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Myo-inositol used for?

What are the side effects of Myo-inositol?

Common side effects of Myo-inositol (≥ 1 in 100): Nausea, Flatulence, Diarrhoea (at >4 g/day doses), Headache. See the Safety section for uncommon and serious reactions.

Is Myo-inositol safe during pregnancy?

Is Myo-inositol compatible with breastfeeding?

Who should not take Myo-inositol?

Myo-inositol is contraindicated in: Known hypersensitivity; Bipolar disorder (myo-inositol theoretically modulates second messenger and may alter lithium effect). Full list in the Safety section.