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Best Myo-Inositol for Cycle Regularity and Ovulatory Support (2026)
Myo-inositol has the strongest evidence base of any inositol form for ovarian function, insulin sensitivity, and cycle regularity. Genazzani 2008 restored menstrual cyclicity in PCOS patients on 2 g/day; Costantino 2009 cut testosterone and triglycerides roughly in half on 4 g/day; the Unfer 2017 meta-analysis of 9 RCTs confirmed reductions in fasting insulin and HOMA-IR. The modern consumer standard for PCOS is the 40:1 myo to D-chiro ratio (Theralogix Ovasitol), which mimics the body's normal plasma ratio and carries NSF Certified for Sport. Pure myo-inositol from NOW, Jarrow, or BulkSupplements is the right pick for IVF preparation, gestational diabetes prevention, or hitting 4 g/day at the lowest cost.
See the full Myo-Inositol scorecard →What the Evidence Says About Myo-Inositol
How A-F grades work- APCOS metabolic profile and ovulation
- BIVF and ICSI oocyte quality in PCOS
- BGestational diabetes prevention in high-risk pregnancy
- CAnxiety, panic disorder, and OCD
- CInsulin sensitivity outside PCOS (metabolic syndrome)
- DType 2 diabetes glycemic control
- BPCOS guideline-level recommendation
A = strong RCT evidence · B = moderate · C = limited · D = weak · F = no evidence.
Our Top Picks
Inositol Powder, 1 lb (Pure Myo-Inositol)
$0.18/day at effective dose
Detailed Reviews
Ovasitol Inositol Powder, 90-Day Supply (Myo + D-Chiro 40:1)
Myo-Inositol + D-Chiro-Inositol (40:1) Powder | 2050mg/serving | 180 servings
The default consumer pick for PCOS metabolic and ovulatory support; for pure myo-inositol see NOW or Jarrow
Inositol Powder, 1 lb (Pure Myo-Inositol)
Pure Myo-Inositol Powder | 730mg/serving | 622 servings
Default value pick for pure myo-inositol at the 4 g/day PCOS, IVF prep, or GDM prevention dose
Inositol Powder, 8 oz (Pure Myo-Inositol)
Pure Myo-Inositol Powder | 600mg/serving | 378 servings
Solid step up from NOW Foods if you already trust Jarrow for other supplements
Also Scored
Inositol Powder, 250g (Pure Myo-Inositol)
$0.48/day | Pure Myo-Inositol Powder
Inositol Powder, 250g (Pure Myo-Inositol)
$0.78/day | Pure Myo-Inositol Powder
Inositol Powder, 1 kg (Pure Myo-Inositol)
$0.15/day | Pure Myo-Inositol Powder
Pure Inositol Powder, 8 oz (Pure Myo-Inositol)
$0.26/day | Pure Myo-Inositol Powder
What to Look For When Buying
- ✓Target 4 g/day total inositol, split as 2 g twice daily, taken with or without food in water
- ✓Theralogix Ovasitol (40:1 myo:DCI ratio, NSF Certified for Sport) is the default consumer pick for PCOS metabolic and ovulatory support
- ✓Pure myo-inositol (NOW Foods, Jarrow, BulkSupplements) is the form used in the IVF egg quality and gestational diabetes prevention trials
- ✓Powder beats capsules on cost - hitting 4 g/day in capsules typically requires 4-8 caps and runs 3-5x more per gram
- ✓Allow 8-12 weeks for insulin and metabolic markers; cycle regularity may take 3-6 months
- ✓Safe to combine with metformin (different but complementary mechanisms); watch for additive hypoglycemia with insulin or sulfonylureas
- ✓Avoid D-chiro-inositol alone above ~600mg/day; the 40:1 ratio is the right format if you want both stereoisomers
Frequently Asked Questions
Myo-inositol vs the 40:1 myo:D-chiro ratio for PCOS, which is better?
Both are reasonable. The 40:1 myo to D-chiro ratio (Ovasitol style) mimics the body's normal plasma ratio and is what most newer PCOS trials use, including the Nordio 2019 ratio comparison study. Pure myo-inositol has the longest research pedigree (Genazzani 2008, Costantino 2009, and the Unfer 2017 meta-analysis) and is what was used in the IVF oocyte quality and gestational diabetes prevention trials. If you want a single recommendation: the 40:1 ratio is the modern consumer default for PCOS, pure myo is the right pick if you are specifically targeting IVF preparation, GDM prevention, or the older mood and anxiety dosing. See the inositol family page for the full ratio comparison.
How long until I see PCOS results from myo-inositol?
Insulin and metabolic markers (fasting insulin, HOMA-IR, SHBG) usually move within 8-12 weeks. Ovulatory restoration and cycle regularity are slower; the Genazzani 2008 trial saw cyclicity return within 12 weeks but most clinicians recommend trialing for at least 3-6 months before judging response. Lipid and androgen changes (testosterone, triglycerides) tracked the 12-week mark in the Costantino 2009 data. Don't expect overnight results.
Is myo-inositol safe during pregnancy?
Yes, at the 4 g/day dose used in the D'Anna 2013 and 2015 gestational diabetes prevention trials. Those studies started myo-inositol in the first trimester and ran through delivery without harm signals to mother or infant. As always, talk to your OB before starting any supplement in pregnancy. The D-chiro-inositol component of the 40:1 ratio has thinner pregnancy data, so if you want to be conservative, pure myo-inositol is the form with the most pregnancy-specific evidence.
Pure myo-inositol vs Ovasitol, which should I buy?
Theralogix Ovasitol is the 40:1 ratio (myo plus a small amount of D-chiro) and is NSF Certified for Sport, the strictest third-party purity standard in the supplement industry. Pure myo-inositol from NOW Foods, Jarrow, or BulkSupplements is the same active molecule as the myo component of Ovasitol but lacks the D-chiro and runs much cheaper per gram. For PCOS, Ovasitol or another 40:1 product is the conventional pick because it matches recent trial protocols. For IVF preparation, GDM prevention, or simply hitting 4 g/day at the lowest cost, pure myo-inositol works.
Capsules vs powder, does it matter?
Form does not matter for absorption, but cost and convenience do. Reaching the 4 g/day clinical dose from capsules typically requires 4-8 capsules per day, which makes capsule formats roughly 3-5x more expensive per gram than powder. Powder mixes cleanly in water and tastes mildly sweet. Capsules are a fair pick if you travel, dislike measuring, or prefer the format; otherwise powder wins on cost and ease at the clinical dose.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products discussed on this page are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.