Myo-Inositol (with D-Chiro-Inositol)
Myo-inositol is a sugar alcohol doing serious signaling work: it's a second messenger inside both the insulin and FSH pathways. In your ovaries specifically, it supports the FSH response and helps the oocyte mature, while also improving insulin sensitivity out in the rest of your body. There's a physiologic ratio at play too, myo- to D-chiro-inositol around 40:1, thought to mirror what's naturally found in healthy follicular fluid. That's exactly why combined formulas get used instead of D-chiro alone: your ovary didn't evolve to run on D-chiro by itself, so why would a supplement work that way.
Evidence
Moderate evidence, and it's specifically strongest in women with PCOS. Several randomized trials and meta-analyses report real improvements in ovulation, menstrual regularity, and insulin markers. The studies themselves are a mixed bag: different doses, different ratios, uneven quality across the board. And if you're looking for data outside PCOS, or specifically for live-birth outcomes, that evidence gets thinner fast.
Interactions
May have additive glucose-lowering effects with insulin-sensitizing medications such as metformin or with other blood-sugar-lowering agents; no major drug interactions are well established, but combined use warrants clinician oversight to avoid low blood sugar.
Cautions
Generally well tolerated; higher doses can cause mild nausea, gas, or loose stools. High-dose D-chiro-inositol alone has been associated in some reports with poorer oocyte quality, which is one reason the myo-dominant ratio is favored. People with diabetes or on glucose-lowering drugs, and anyone pregnant or trying to conceive, should confirm dose and formulation with a clinician.
Food sources
Found naturally in fruits (especially cantaloupe and citrus), beans, whole grains, nuts, and buckwheat, though dietary amounts are far below therapeutic study doses.
