Myo + D-Chiro Inositol 40:1 by Fairhaven Health

This inositol blend is aimed at women who want to support regular cycles and ovulation, including those preparing for pregnancy. It fits best when irregular cycles travel with signs of insulin resistance, so useful labs to have before you start are Insulin, HbA1c, Total Testosterone and SHBG. If your periods are absent, very irregular or have changed suddenly, see your clinician first: a supplement should not delay finding the cause.

Myo-inositol and D-chiro-inositol are closely related compounds the body makes from glucose and also gets from fruit, beans and grains. Inside cells they act as messengers that help relay the signals of insulin and of FSH, the hormone that drives follicle growth. The 40:1 ratio mirrors the proportion normally found in blood. Most of the research comes from women with polycystic ovary syndrome (PCOS), in whom inositol has been studied for insulin sensitivity and cycle regularity. Results are encouraging, but the trials are small, and the evidence for egg quality in particular is mixed.

The label directs 4 capsules daily with a meal. Together they provide 2,000 mg of myo-inositol and 50 mg of D-chiro-inositol. Taking them with food also lowers the chance of stomach upset. Many trials used about twice this daily amount, split morning and evening, and the label says to take it only as directed, so ask your clinician which amount fits you before taking more.

Inositol can modestly lower blood sugar and insulin, so check with your clinician before combining it with metformin, insulin or other glucose-lowering medicines. If you are working with a fertility clinic, tell them you are taking it. If you become pregnant or are nursing, ask your obstetric clinician whether to continue. Side effects are uncommon at this amount and are mostly mild nausea, gas or loose stools.

Cycles change slowly. Allow about three months of steady daily use before judging, and track cycle length as you go. Inositol does not replace a prenatal vitamin or folate if you are trying to conceive, and it does not stand in for a medical evaluation of irregular periods. Compared with myo-inositol alone, the 40:1 blend adds a small amount of D-chiro-inositol; whether that improves results is still debated.