Inositol
myo-Inositol
Also known as: myo-Inositol, D-chiro-inositol, Vitamin B8 (former), myo-Ins, MI:DCI ratio
Inositol is a sugar alcohol structurally similar to glucose that acts as a second messenger for insulin and neurotransmitters. It shows promise for PCOS, insulin resistance, and mood disorders.
Introduction
Inositol is a naturally occurring sugar alcohol that was once classified as vitamin B8 until it was discovered that the body can synthesize it from glucose. It exists in nine stereoisomeric forms, with myo-inositol being the most abundant and biologically relevant.
Myo-inositol serves as a precursor for inositol phosphates and phosphatidylinositol, which act as second messengers for several hormones and neurotransmitters, including insulin, FSH, TSH, and serotonin. This signaling role explains its broad effects on metabolism and mood.
Inositol has gained significant attention for polycystic ovary syndrome (PCOS), where it improves insulin sensitivity, restores ovulation, and improves fertility outcomes. The 40:1 ratio of myo-inositol to D-chiro-inositol mimics the physiological ratio found in healthy women.
Beyond PCOS, inositol shows promise for metabolic syndrome, gestational diabetes, and mood disorders. Studies suggest it may help with panic disorder, obsessive-compulsive disorder (OCD), and depression, possibly through modulation of serotonin and dopamine signaling.
Because inositol is well-tolerated with minimal side effects, it represents an attractive natural approach for several conditions, particularly for women seeking alternatives to hormonal treatments for PCOS.
Main Benefits
Improves insulin sensitivity and reduces insulin resistance in PCOS, metabolic syndrome, and gestational diabetes.
Restores ovulation and improves fertility outcomes in women with PCOS.
May reduce symptoms of panic disorder, anxiety, and obsessive-compulsive disorder (OCD) through modulation of serotonin signaling.
Improves metabolic parameters including blood glucose, HbA1c, and lipid profiles in insulin-resistant conditions.
May reduce gestational diabetes risk and improve pregnancy outcomes in at-risk women.
Mechanism of Action
Inositol functions primarily as a second messenger precursor in cellular signaling:
Insulin Signaling: Myo-inositol is incorporated into phosphatidylinositol phosphate (PIP2) in cell membranes. When insulin binds to its receptor, PIP2 is cleaved to IP3 (inositol trisphosphate) and DAG (diacylglycerol). IP3 triggers calcium release, mediating insulin's cellular effects. In insulin resistance, this pathway is impaired.
FSH Signaling: In ovarian cells, inositol phosphates serve as second messengers for FSH (follicle-stimulating hormone). Supplementation may improve ovarian response to FSH, explaining benefits in PCOS and fertility.
Neurotransmitter Modulation: Inositol influences serotonin, dopamine, and glutamate signaling. It is involved in the phosphatidylinositol cycle, which is disrupted in some mood disorders. This may explain its effects on anxiety and depression.
D-chiro-inositol Function: DCI is produced from myo-inositol by an epimerase enzyme. In PCOS women, this conversion is often impaired. DCI specifically mediates insulin's glycogen synthesis effects and has independent roles in androgen synthesis modulation.
Osmotic Regulation: Inositol acts as an organic osmolyte, helping cells maintain volume and protect against osmotic stress.
Natural Sources
Inositol is found in many foods, particularly fruits, beans, grains, and nuts. The body can also synthesize it from glucose.
Examples:
Citrus fruits (oranges, grapefruit)
Cantaloupe
Beans (kidney, navy, lima)
Brown rice
Wheat germ
Oats
Nuts (almonds, walnuts)
Bananas
Raisins
Cabbage
Found in whole foods; body synthesizes from glucose; therapeutic doses for PCOS/mood disorders exceed typical dietary intake.
Recommended Daily Intake
No established RDA or AI. Therapeutic doses vary by condition: PCOS typically 2-4 g myo-inositol daily; anxiety/panic studies used 12-18 g daily.
Reference Values:
| PCOS (myo-inositol) | 2-4 g/day |
| PCOS (40:1 MI:DCI) | 2-4 g/day (contains ~100 mg DCI) |
| Gestational diabetes | 2-4 g/day |
| Anxiety/panic disorders | 12-18 g/day |
| General metabolic support | 1-2 g/day |
Sources for RDI/AI:
The 40:1 ratio of myo-inositol to D-chiro-inositol is considered optimal for PCOS as it mimics the physiological ratio. Higher DCI ratios may be detrimental to egg quality.
Effectiveness for Specific Focuses
Strong evidence for PCOS; restores ovulation; improves fertility; supports gestational diabetes management.
Improves insulin sensitivity; reduces metabolic syndrome parameters; supports healthy glucose metabolism.
Promising evidence for panic disorder, OCD, and anxiety; modulates serotonin signaling; well-tolerated alternative to SSRIs for some.
May indirectly improve sleep through anxiety reduction; limited direct evidence for sleep enhancement.
Safety Information
Potential Side Effects
Mild nausea at high doses
Diarrhea or loose stools (dose-dependent)
Headache (rare)
Dizziness (rare)
Contraindications
Bipolar disorder (theoretical concern about mania induction)
Overdose Information
Extremely safe; water-soluble; minimal toxicity even at high doses (up to 18 g studied); main side effect is GI upset.
Exceptional safety profile. Very well-tolerated even at high therapeutic doses.
Interactions
Drug Interactions:
Lithium (inositol may oppose lithium effects)
Anti-anxiety medications (may have additive effects)
Diabetes medications (may enhance glucose-lowering effects)
May oppose lithium effects; caution with diabetes medications due to glucose-lowering effects; generally compatible.
Other Supplement Interactions:
Chromium - synergistic for insulin sensitivity
Alpha-lipoic acid - complementary metabolic effects
Folate and B12 - support methylation pathways
Synergistic with other insulin-sensitizing supplements; safe combinations.
Start with lower doses and titrate up to minimize GI upset. The 40:1 myo-inositol to D-chiro-inositol ratio is preferred for PCOS. Avoid high-dose DCI alone for fertility purposes.
Forms and Bioavailability
Myo-inositol is the primary form. D-chiro-inositol is a specific isomer with distinct metabolic effects. Combined products use a 40:1 ratio.
myo-Inositol
The most abundant natural form; well-absorbed; serves as precursor for second messengers.
Good oral bioavailability; reaches tissues effectively; well-studied form.
Standard form for PCOS, fertility, and mood support. Most research uses this form.
D-chiro-Inositol (DCI)
Specific stereoisomer with distinct metabolic effects; produced from myo-inositol in body.
Well-absorbed but different tissue distribution; specialized effects on glycogen synthesis.
Use only in combination with myo-inositol (40:1 ratio) or for specific metabolic purposes. Avoid high-dose DCI alone for fertility.
40:1 myo:DCI Combination
Combined product mimicking physiological ratio found in healthy women.
Optimal ratio for PCOS; provides both forms in physiologically appropriate amounts.
Preferred form for PCOS. Look for products providing ~2-4 g myo-inositol with ~50-100 mg DCI.
Warnings & Suitability
Did You Know...?
Inositol was once called "vitamin B8" until researchers discovered humans can synthesize it from glucose, making it no longer technically a vitamin.
The 40:1 ratio of myo-inositol to D-chiro-inositol in healthy women's blood was the key discovery that led to effective PCOS supplementation protocols.
Myo-inositol concentrations in the brain are 100-1000 times higher than in blood, highlighting its importance for neurological function.
Inositol is found in high concentrations in the heart, brain, and ovaries - tissues with high metabolic activity.
General Scientific Sources
Tags
Content Verification
Last Medical Review: 2/13/2026
Reviewed by: Editorial Team