Myo-Inositol: What It Is, What It Does, and Who Takes It
Myo-Inositol has become one of the more heavily researched supplements in women's health over the past decade — particularly in relation to PCOS. If you've arrived here from that direction, this article will give you an accurate picture of what the evidence actually says.
It's also worth reading if you've encountered Myo-Inositol in a different context — mental health, thyroid support, metabolic health — where a smaller but growing body of research also exists.
This article covers what Myo-Inositol is, how it works, what the evidence supports, and how to choose between the powder and capsule formats.
What Is Myo-Inositol?
Inositol is a naturally occurring carbohydrate-like compound found throughout the body and in a wide range of foods — fruits, beans, whole grains, nuts, and seeds are among the better dietary sources. It is sometimes informally referred to as Vitamin B8, though this is technically inaccurate: unlike true vitamins, inositol can be synthesised by the body from glucose and is therefore not classified as an essential vitamin.
There are nine naturally occurring forms of inositol (stereoisomers), but two are of primary biological relevance:
- Myo-Inositol (MI) — the most abundant form in the body, present in virtually every tissue and involved in a wide range of cellular signalling processes
- D-Chiro-Inositol (DCI) — present in smaller quantities, converted from Myo-Inositol by an enzyme, and involved in specific metabolic pathways
The ratio of MI to DCI varies between tissues and is tightly regulated by the body. Disruption of this ratio — particularly in ovarian tissue — is a significant focus of current research in PCOS.
Health Leads supplies Myo-Inositol in its pure form, sourced from phytin derived from corn (maize). Non-GMO. No other ingredients.
Inositol occurs naturally in fruits, legumes, whole grains, and nuts — with Myo-Inositol being the most abundant form in food and in the body.
How Does Myo-Inositol Work?
Myo-Inositol functions primarily as a second messenger in cellular signalling — it's involved in how cells receive and respond to hormonal signals. Two pathways are particularly relevant to its most studied applications:
Insulin signalling: Myo-Inositol plays a role in the intracellular cascade that follows insulin binding to its receptor. When insulin signalling is impaired — a condition known as insulin resistance — the downstream effects include elevated blood glucose, compensatory hyperinsulinaemia, and a range of metabolic consequences. Myo-Inositol has been investigated as a means of supporting insulin signal transduction at a cellular level.
FSH signalling in the ovary: Myo-Inositol is a secondary messenger in follicle-stimulating hormone (FSH) signalling in ovarian follicles. It is required for normal follicular development. Research has shown that in women with PCOS, ovarian Myo-Inositol levels are often depleted — and that restoring these levels may support follicular maturation and normal ovarian function.
Myo-Inositol and PCOS — What the Evidence Shows
This is where the most substantive body of research sits. PCOS (polycystic ovary syndrome) is a complex endocrine condition affecting approximately 8–13% of women of reproductive age globally. Its presentation varies considerably, but commonly involves irregular ovulation or anovulation, elevated androgens, insulin resistance, and polycystic-appearing ovaries on ultrasound.
The research on Myo-Inositol in PCOS is more developed than for most supplement applications — there are multiple randomised controlled trials, systematic reviews, and meta-analyses. The evidence base is substantive, not merely anecdotal.
What the research consistently shows:
- Myo-Inositol supplementation is associated with improvements in menstrual regularity in women with PCOS and anovulatory cycles
- It is associated with reductions in fasting insulin and improvements in insulin sensitivity markers in women with PCOS and insulin resistance
- It is associated with reductions in testosterone and other androgen markers in some studies — relevant to symptoms such as excess hair growth and acne
- Studies in the context of assisted reproduction (IVF) have shown improvements in oocyte quality and embryo quality in women with PCOS supplementing with Myo-Inositol
The MI:DCI ratio: Research has established that the optimal ratio of Myo-Inositol to D-Chiro-Inositol in supplementation appears to be 40:1 — reflecting the physiological ratio found in healthy ovarian tissue and in plasma. Many studies use a combined MI/DCI formula at this ratio. Pure Myo-Inositol supplementation is still the more widely studied approach and has a strong evidence base independently; the ratio-specific research adds a further layer of nuance that some practitioners use when advising on combined supplementation.
Doses used in research: Clinical studies in PCOS have typically used doses of 2–4g of Myo-Inositol per day, often divided across two doses. This is significantly higher than what a standard capsule provides at one capsule daily — at 500mg per capsule, the research dose range corresponds to 4–8 capsules per day, or 2–4 level scoops of the powder. The product pages allow for up to 3 capsules or 3 scoops daily. If you are supplementing with Myo-Inositol specifically in the context of PCOS at research-level doses, seek advice from a qualified healthcare professional.
Other Areas of Research
PCOS is the most extensively studied application, but Myo-Inositol appears in several other areas of ongoing research:
Mental Health
Myo-Inositol is a precursor to the phosphoinositide second messenger system used in serotonin, dopamine, and other neurotransmitter signalling pathways. Early research — including randomised controlled trials — found positive signals in panic disorder and OCD at doses of 12–18g per day. More recent research has been more mixed. The mental health application requires doses substantially higher than standard supplementation and should not be undertaken without professional guidance. This remains an active area of research rather than a settled application.
Thyroid Health
A more recent area of interest involves Myo-Inositol in the context of thyroid autoimmunity, particularly Hashimoto's thyroiditis. Some research has investigated combined Myo-Inositol and selenium supplementation in reducing thyroid antibody levels. This research is preliminary — interesting but not yet at a level that warrants strong claims.
Gestational Diabetes
Several studies have investigated Myo-Inositol supplementation during pregnancy as a means of reducing the risk of gestational diabetes in at-risk women. The evidence is promising but not yet definitive, and any supplementation during pregnancy should be discussed with a GP or midwife.
Metabolic Health
Beyond the PCOS context, Myo-Inositol has been studied in relation to insulin resistance and metabolic syndrome more broadly. The evidence here is less developed than in PCOS but the mechanistic rationale — supporting insulin signal transduction — applies to metabolic dysfunction generally.
What There Are No Claims For
Unlike some nutrients, Myo-Inositol has no EU-approved health claims. This means that supplement manufacturers — including Health Leads — cannot legally make specific health benefit claims about it on product labels or in marketing.
This doesn't reflect a lack of evidence. It reflects the fact that the health claim approval process is separate from and slower than the research literature. The clinical trial evidence for Myo-Inositol in PCOS is genuine and meaningful — it just hasn't been through the EU EFSA health claim approval pathway.
What this means practically: Myo-Inositol is a food supplement, not a medicine. It is not a treatment for PCOS, which is a diagnosed medical condition requiring appropriate medical care. Women with PCOS should be under the care of a GP or specialist and should discuss any supplementation with their healthcare team.
Powder or Capsules — Which Format Is Right for You?
Health Leads offers Myo-Inositol in two formats. The choice depends primarily on your intended dose and preference for convenience.
Myo-Inositol Powder 300g — £24.40
Pure Myo-Inositol powder with zero other ingredients. Supplied with a 1ml measuring scoop (approximately 700mg per level scoop). Mix one scoop with approximately 75ml of water — the powder dissolves readily and is unflavoured with a mildly sweet taste.
Up to three servings daily. 300g provides a substantial supply at lower doses, or a meaningful amount at higher doses closer to those used in research.
The powder format is the more practical choice for those supplementing at higher daily doses, as it allows flexible, cost-effective dosing without swallowing multiple capsules.
View Myo-Inositol Powder 300g →
Myo-Inositol 500mg x 90 Capsules — £13.70
500mg of pure Myo-Inositol per HPMC vegetable capsule. No fillers, no flow agents, no other ingredients. One to three capsules daily with food — providing 500mg to 1500mg per day.
At one capsule daily: 90-day supply. At three capsules daily: 30-day supply.
The capsule format is more convenient for everyday use at lower to moderate doses and requires no measuring or mixing.
View Myo-Inositol 500mg Capsules →
What's in Both Products
| Powder 300g | Capsules 500mg x 90 | |
|---|---|---|
| Active ingredient | Myo-Inositol 100% | Myo-Inositol 500mg |
| Other ingredients | None | HPMC capsule shell only |
| Fillers / flow agents | None | None |
| Source | Phytin from corn (maize), non-GMO | Myo-Inositol (vegan) |
| Vegan | Yes | Yes |
| Flexible dosing | Yes — scoop included | 1–3 capsules daily |
| Price | £24.40 | £13.70 |
Both made in Wales by Health Leads, ISO accredited, additive-free since 1998.
The Bottom Line
Myo-Inositol has one of the stronger evidence bases in the women's health supplement category, particularly for PCOS. The research is not perfect — no supplement research is — but the volume, quality, and consistency of findings across multiple trials is meaningful and represents more than marketing.
The key points to take from the evidence: the doses used in clinical research are typically 2–4g per day; the effects studied are on menstrual regularity, insulin sensitivity, androgen levels, and reproductive outcomes in women with PCOS; and PCOS is a medical condition that warrants professional care alongside any supplementation approach.
Beyond PCOS, the research in mental health and metabolic health is interesting but less conclusive. The thyroid and gestational diabetes applications are preliminary.
Both formats — powder and capsules — provide 100% pure Myo-Inositol with no additives. The choice between them comes down to dose preference and convenience.
Health Leads Myo-Inositol — 100% pure Myo-Inositol, non-GMO, additive-free. Available as powder (300g, £24.40) or capsules (500mg x 90, £13.70). No fillers. No flow agents. Vegan. Made in Wales. ISO accredited. Additive-free since 1998.