Myo-Inositol Supplement Ireland: Evidence Guide, PCOS, Dosage & Where to Buy
Myo-inositol is a naturally occurring carbohydrate, often mistaken for a B vitamin, that has attracted significant research attention, particularly in the context of PCOS and hormonal health. This guide explains what it is, what the evidence actually shows, how supplement doses compare with research doses, and how to choose between the four inositol capsule products stocked in Ireland by Probiotic.ie.
Myo-inositol is a naturally occurring carbohydrate (a cyclic polyol) found in grains, legumes and fruit, and made in the body from glucose. It is not a vitamin, although it is still sometimes called vitamin B8. It is the most abundant of nine inositol forms and acts as a second messenger in insulin signalling pathways.
In Ireland, myo-inositol supplements are food supplements under FSAI and HPRA oversight. They are not medicines, are not novel foods, carry no authorised EU health claim under Regulation 1924/2006, and attract Irish VAT at 13.5%.
The strongest human evidence is in PCOS: a 2012 systematic review by Unfer et al. (PMID 22296306) of 13 RCTs reported improvements in menstrual regularity, ovulation rate and hormonal markers at 4 g/day. Standard capsules provide 500 to 650 mg per capsule, well below that dose. Psychiatric research used 12 to 18 g/day.
What has not been proven: inositol is not an established treatment for PCOS, anxiety, OCD or any other condition. It is not interchangeable with d-chiro-inositol, and high-dose d-chiro-inositol on its own has raised concerns about egg quality in some research.
Probiotic.ie stocks four inositol capsule products in Dublin: NOW Foods Inositol 500mg, Osavi Inositol 600mg, Swanson Inositol 650mg and NOW Foods Choline & Inositol. Compare them in the inositol collection.
- Women with PCOS looking for evidence on myo-inositol, dosage, and the myo vs d-chiro-inositol distinction
- Anyone comparing inositol supplement options in Ireland: capsules vs powder, dose per capsule, vegan vs gelatine, solo inositol vs choline & inositol
- People researching inositol dosage and wanting to understand how supplement doses relate to clinical trial doses
- Anyone asking about side effects or safety of inositol supplements in Ireland
Not a guide for: Treating or managing PCOS, anxiety, OCD, or any medical condition. If you have a diagnosed condition, consult your GP before using supplements.
Myo-inositol (also written myo inositol, or simply inositol) definition: A naturally occurring cyclic polyol, historically called vitamin B8 although it is not a vitamin, synthesised in the body from glucose-6-phosphate in the kidneys and liver, and found in grains, legumes, citrus fruits and nuts, with highest tissue concentrations in the brain, testes and skeletal muscle.
A myo-inositol supplement in Ireland is a food supplement providing isolated myo-inositol, in capsule or powder form, regulated by the FSAI as a food supplement rather than a medicine. It is not a hormone, not a drug, and carries no authorised EU health claim. The compound occurs naturally in food and is produced in the body. The most studied use case is in women with PCOS, where systematic reviews suggest a potential supportive role in hormonal and metabolic markers at 4 g/day, though inositol is not an approved PCOS treatment. Capsule products in Ireland typically provide 500 to 650 mg of myo-inositol per capsule; powder is the practical format for gram-level intakes. Four capsule options are compared in the inositol collection.
- What it is: A naturally occurring cyclic polyol (a carbohydrate); produced in the body from glucose-6-phosphate. Not a vitamin.
- Why it is called vitamin B8: A historical label from when inositol was thought to be essential. The body makes its own, so it does not meet the definition of a vitamin. Some brands still file it under vitamin B.
- Most abundant form: Myo-inositol, the primary isomer in human tissue and in food. "Inositol" on a supplement label means myo-inositol unless another form is named.
- Dietary sources: Wholegrains, legumes (beans, lentils), citrus fruits, nuts, cantaloupe; typically 1 to 2 g/day from a varied diet
- Endogenous production: The kidneys produce approximately 2 g of inositol per day from glucose-6-phosphate
- Clinical trial dose range: 2 to 4 g/day in PCOS research; 12 to 18 g/day in psychiatric research (Levine et al., Palatnik et al.)
- Is it a hormone or stimulant? No. Inositol is a carbohydrate that functions as a cell-signalling molecule; it is not a hormone, steroid or stimulant
- EU novel food status: Myo-inositol is not a novel food. D-chiro-inositol was confirmed as not novel in food supplements by the European Commission in 2025, resolving earlier doubts raised by some member states.
- Vegetarian/vegan suitable? Depends on the capsule. NOW and Osavi use hypromellose (cellulose) capsules; Swanson uses gelatine. Powder is inositol only.
- Irish regulatory status: Food supplement under FSAI and HPRA oversight; not a medicine; no disease treatment claims permitted
- Irish VAT rate on supplements: 13.5%
- Myo-inositol is not a vitamin. The "vitamin B8" name is historical; the body synthesises inositol, so it fails the definition
- Myo-inositol is not a hormone and does not directly alter oestrogen, progesterone or testosterone levels
- Myo-inositol is not d-chiro-inositol; they are distinct stereoisomers with different tissue distributions and proposed mechanisms
- Myo-inositol is not an approved treatment for PCOS, anxiety, OCD or any other medical condition in Ireland or the EU
- Myo-inositol at 500 mg to 2 g/day is not the dose used in psychiatric research; psychiatric trials used 12 to 18 g/day
- Myo-inositol is not a stimulant, fat burner or weight-loss supplement; there is no established evidence for weight loss in healthy populations
- Myo-inositol supplements do not carry any authorised EU health claim under Regulation 1924/2006
What is well-supported: Improvements in menstrual regularity, ovulation rate and hormonal markers (LH/FSH ratio, androgens) in women with PCOS at 4 g/day. Unfer et al. systematic review of 13 RCTs (Gynecol Endocrinol, 2012, PMID 22296306).
What is not proven: Inositol has not been established as a treatment for any medical condition. Psychiatric research used doses (12 to 18 g/day) far above standard supplements. Evidence outside PCOS is preliminary. No trial evidence exists at the 500 to 650 mg one-capsule dose.
Most relevant human dose range: 2 to 4 g/day in PCOS studies; 500 mg to 1 g/day in standard capsule format.
Key safety note: High-dose d-chiro-inositol alone may negatively affect oocyte quality. Myo-inositol is generally well tolerated at supplement doses; GI side effects reported at doses above 12 g/day.
| Feature | Detail | Evidence Level |
|---|---|---|
| PCOS — menstrual regularity | Systematic review of 13 RCTs; improvements reported | RCT Evidence |
| PCOS — ovulation rate | Unfer et al. 2012; improvement vs placebo | RCT Evidence |
| Panic disorder | Palatnik et al. 2001; 18 g/day crossover RCT, n=20 | Small RCT |
| OCD | Fux et al. 1996; 18 g/day, n=13; preliminary only | Preliminary |
| Depression | Levine et al. 1995; 12 g/day, positive; subsequent meta-analysis mixed | Mixed |
| Insulin sensitivity (PCOS) | Croze & Soulage 2013; IPG second-messenger pathway proposed | Mechanistic |
| Healthy adults — mood, cognition | No established RCT evidence at supplement doses | Not established |
| Irish regulatory status | FSAI food supplement; not a medicine; not a novel food | Confirmed |
- What is myo-inositol? Types and forms explained
- Myo-inositol and PCOS: what the evidence shows
- Myo-inositol benefits: mechanisms and research
- Inositol dosage: 500 mg, 2 g and 4 g compared
- Inositol capsules vs powder
- Inositol side effects and safety
- Choline and inositol: the combination supplement
- Inositol supplements in Ireland: the four products compared
- Regulation in Ireland and where to buy
- Frequently asked questions
What Is Myo-Inositol? Types and Forms Explained
Inositol is a cyclic polyol, structurally similar to glucose, that occurs naturally in nine stereoisomeric forms. Of these, myo-inositol is by far the most biologically significant, accounting for the majority of inositol present in human tissue, food and commercially available supplements.[7]
The compound was historically grouped with the B vitamins and given the name vitamin B8. It is not a vitamin: the human body synthesises it from glucose-6-phosphate, primarily in the kidneys and liver, at approximately 2 g per day. Some manufacturers still list inositol under vitamin B, which is a legacy of that naming rather than a statement about its biology. The EU has set no Nutrient Reference Value for inositol, which is why supplement labels show no percentage against it.
The term "inositol" on a supplement label almost always refers to myo-inositol unless otherwise stated. D-chiro-inositol is a distinct stereoisomer produced from myo-inositol by an epimerase enzyme, and some combination products contain both. The physiological ratio of myo-inositol to d-chiro-inositol in human plasma is approximately 40:1; in ovarian tissue the ratio is similar.[2]
Inositol powder and capsule supplements typically contain only myo-inositol. Products labelled "myo-inositol and d-chiro-inositol" or "40:1 ratio" contain both isomers at the specified ratio, which some researchers have proposed as closer to the physiological distribution. The clinical evidence specifically for 40:1 combination products is more limited than for myo-inositol alone.
Myo-inositol is a food supplement ingredient regulated under Directive 2002/46/EC and FSAI guidance. It is not a medicine and not a novel food. D-chiro-inositol's status was less clear until 2025, when the European Commission updated the Novel Food Status Catalogue to record it as not novel in food supplements, following questions raised by Spanish authorities about its use before May 1997.[8] No EU health claim is authorised for either form under Regulation 1924/2006. Any product claiming to treat, cure or prevent a disease would be misrepresenting its regulatory status.
Myo-Inositol and PCOS: What the Evidence Shows
PCOS (polycystic ovary syndrome) is the most extensively researched clinical application of myo-inositol, and the use case with the strongest available human evidence. The proposed mechanism involves inositol's role as a second messenger in insulin receptor signalling. In women with PCOS, impaired insulin sensitivity is a common feature, and inositolphosphoglycan (IPG) molecules derived from inositol appear to play a mediating role in how cells respond to insulin.[7]
The key systematic review was conducted by Unfer et al. from Università di Roma and published in Gynecological Endocrinology in 2012 (PMID 22296306). It covered 13 RCTs and reported that myo-inositol supplementation at 4 g/day was associated with improvements in menstrual regularity, ovulation rate and hormonal markers including the LH/FSH ratio and androgen levels, compared with placebo. Some included trials used an active comparator.[1]
A subsequent clinical guidance paper by Barrea et al. (Expert Reviews in Endocrinology & Metabolism, 2021, PMID 33827343) outlined the evidence base and proposed that myo-inositol, particularly combined with d-chiro-inositol at a 40:1 ratio, may support hormonal and metabolic outcomes in PCOS patients under medical supervision.[3]
PCOS is a complex hormonal condition requiring diagnosis and medical management. The research discussed here relates to myo-inositol as a studied nutritional compound. It should not be read as evidence that an inositol supplement treats, cures or manages PCOS. Anyone with PCOS or suspected PCOS symptoms should consult their GP or a specialist. Inositol supplementation, if considered, should be discussed with a healthcare professional who can advise on dose and monitoring.
The clinical and mechanistic research discussed in this article relates to myo-inositol as a studied compound. It should not be read as a claim that any inositol product sold by Probiotic.ie produces these effects. These products are food supplements, not medicines. No authorised EU health claim is made for inositol on this page or on the products.
Inositol capsules stocked in Dublin
Four single-format options: 500 mg, 600 mg and 650 mg single-ingredient capsules, plus a 250/250 mg choline and inositol combination. All myo-inositol. Tracked DPD delivery from Dublin.
Myo-Inositol Benefits: Mechanisms and Research
Inositol's proposed biological roles span several physiological systems. As a component of phosphatidylinositol, a key phospholipid in cell membranes, it is involved in multiple second-messenger cascades that regulate how cells communicate and respond to external signals.[7]
It is important to distinguish between mechanisms demonstrated in vitro or in animal models and outcomes established in human clinical trials. Many proposed inositol mechanisms are based on cell culture or animal research. The human evidence is strongest for PCOS-related hormonal markers, and more limited or preliminary elsewhere.
Inositol Dosage: 500 mg, 2 g and 4 g — What the Research Uses
Inositol dosage is one of the most searched questions, and one where supplement labels, popular advice and clinical research diverge significantly. The dose on a capsule label is not the same as the dose studied in clinical trials. Understanding that gap matters before drawing conclusions from published research.
Inositol dose at a glance: 500 mg, 2 g and 4 g compared
| Dose Level | Typical Format | Research Context | Evidence Basis |
|---|---|---|---|
| 500 to 650 mg/day | 1 capsule (the label dose on NOW 500 mg, Osavi 600 mg and Swanson 650 mg) | Nutritional supplement; general use | Below all clinical trial doses; no specific evidence at this level |
| 2 g/day | 3 to 4 capsules; or powder | Entry-level PCOS research dose; some metabolic studies | Below primary PCOS trial dose; consult GP before use at this level |
| 4 g/day | Powder (2 × 2 g with meals) | Primary PCOS research dose (Unfer et al. 2012) | RCT systematic review (13 trials); consult GP required |
| 12 to 18 g/day | Powder only; not practical in capsule form | Psychiatric research only (depression, panic, OCD) | Small early-stage trials (n=13 to 20); not recommended without specialist supervision |
Every capsule product stocked by Probiotic.ie directs one capsule daily on the label, giving 500 to 650 mg of myo-inositol depending on the product. That is the labelled dose and is well below any intake associated with GI side effects in the published literature. Anyone wanting to follow PCOS research protocols at 4 g/day should discuss this with their GP first, and would typically use an inositol powder for practical dosing at that level.
Inositol capsules vs powder: which format?
The ingredient is identical in both formats. The difference is practical. Capsules give a fixed, measured dose with no taste and no scoop, which suits people who want a set daily amount and are happy at the 500 to 650 mg range. Powder suits people who want to take gram-level amounts, or adjust the quantity, because reaching 2 to 4 g/day from capsules means four to eight capsules a day. Powder dissolves in water and has a mildly sweet taste; inositol is technically a polyol, the same class as sugar alcohols, though at these amounts it contributes negligible energy. Probiotic.ie currently stocks capsules only.
Early psychiatric research by Levine et al. (Am J Psychiatry, 1995, PMID 7726322) and Palatnik et al. (J Clin Psychopharmacol, 2001, PMID 11386498) explored inositol at 12 to 18 g/day in depression, panic disorder and OCD in small trials (n=13 to 20). Results were mixed: the panic disorder crossover showed a significant reduction in attack frequency vs fluvoxamine; the depression data was inconsistent across studies. These are hypothesis-generating findings, not practice-changing ones. The doses used are 20 to 36 times a standard capsule. Anxiety, OCD and depression require professional diagnosis and management and should not be self-treated with supplements. For compounds with a more established stress evidence profile, see our L-theanine Ireland guide and Rhodiola Rosea guide.
Inositol Side Effects and Safety
At standard nutritional supplement doses (500 mg to 2 g/day), myo-inositol is generally considered well tolerated. The most commonly reported side effects, seen in high-dose psychiatric research, are gastrointestinal: nausea, flatulence and loose stools. These effects are dose-dependent and have been observed primarily at doses of 12 g/day and above.[5]
No serious adverse events have been attributed to myo-inositol at supplement doses in the published clinical literature. There is no established concern for liver, kidney or cardiovascular toxicity at nutritional intake levels. Inositol is found naturally in food and produced in the body; the body has established pathways for handling it.
Key cautions: bipolar disorder may be a contraindication for high-dose inositol, as some case reports have raised concerns about mood cycling; this applies to very high doses and is not established at 500 mg levels. Pregnancy and breastfeeding: insufficient safety data exists for supplemental doses in these groups, so consult a GP before use. Drug interactions: no significant pharmacokinetic interactions have been established, but anyone on prescribed medication for PCOS or blood glucose management should inform their doctor.
Some clinical literature has raised concerns about high-dose inositol and mood cycling in individuals with bipolar disorder. This applies to doses used in psychiatric research (12 to 18 g/day), not to supplement doses. However, anyone with a history of bipolar disorder should consult a psychiatrist before using inositol supplements at any dose.
Choline and Inositol: The Combination Supplement
Choline and inositol are often paired in one capsule. Neither is a vitamin, although both were once grouped with the B vitamins. Both are components of key membrane phospholipids, phosphatidylcholine and phosphatidylinositol, which is the rationale for combining them.
The regulatory position of the two ingredients differs. Choline is an essential nutrient with three authorised EU health claims under Regulation 432/2012: choline contributes to normal lipid metabolism, choline contributes to normal homocysteine metabolism, and choline contributes to the maintenance of normal liver function. The condition for using these claims is at least 82.5 mg of choline per 100 g, per 100 ml or per single portion.[9] EFSA has set an adequate intake of 400 mg of choline per day for adults. Inositol carries no authorised claim. Combining them does not create new evidence for the combination; each ingredient keeps its own profile.
NOW Foods Choline & Inositol provides 250 mg of choline (from 630 mg choline bitartrate) and 250 mg of inositol per capsule. At 250 mg of choline per capsule it meets the 82.5 mg condition, so the authorised choline claims apply to that product. It gives half the inositol of the single-ingredient 500 mg capsule.
Inositol Supplements in Ireland: The Four Products Compared
Four inositol capsule products are stocked in Dublin. All use myo-inositol, all are 100-capsule bottles, and all direct one capsule daily. They differ on three things: how much inositol is in each capsule, what the capsule shell is made of, and whether choline is included.
| Product | Inositol per capsule | Other active | Capsule shell | Vegan |
|---|---|---|---|---|
| Swanson Inositol 650mg | 650 mg | None | Gelatine | No |
| Osavi Inositol 600mg | 600 mg | None (inulin as filler) | HPMC (vegan) | Yes |
| NOW Foods Inositol 500mg | 500 mg | None | Hypromellose (vegan) | Yes |
| NOW Foods Choline & Inositol | 250 mg | 250 mg choline | Hypromellose (vegan) | Yes |
Choose by dose if inositol alone is the goal: Swanson gives the most per capsule, then Osavi, then NOW. Choose Osavi or NOW if you need a vegan capsule. Choose Choline & Inositol if you specifically want both nutrients in one capsule and are content with 250 mg of inositol. Current prices are on each product page and in the inositol collection.
Regulation in Ireland and Where to Buy
In Ireland, myo-inositol supplements are food supplements regulated by the Food Safety Authority of Ireland (FSAI) under Directive 2002/46/EC, with the HPRA as the medicines authority that determines they are not medicinal products. They carry no authorised health claim under Regulation 1924/2006 and do not require a prescription. Irish VAT at 13.5% is included in all prices at Probiotic.ie.
Probiotic.ie is an authorised Irish retailer for NOW Foods and Osavi. All four inositol products are dispatched from Dublin with tracked DPD delivery across Ireland, free on orders over €75, with no customs charges because the stock ships from within Ireland. UK customers should visit probiotic.co.uk.
Product details on this page (myo-inositol per capsule, other actives, capsule shell, capsule count and directions) were verified by Probiotic.ie against manufacturer supplement-facts panels on 3 September 2026. Prices are deliberately not stated here because they change; the live price is on each product page. Always check the current label before use.
The clinical and mechanistic research discussed in this article relates to myo-inositol as a studied compound. It should not be read as a claim that any inositol product sold by Probiotic.ie produces these effects. These products are food supplements, not medicines. No authorised EU health claim is made for inositol on this page or on the products.
Four inositol products, one Dublin warehouse
Authorised Irish retailer for NOW Foods and Osavi. Tracked DPD delivery from Dublin. Free over €75.
- Myo-inositol is a naturally occurring cyclic polyol (a carbohydrate), produced in the body at approximately 2 g/day and found in grains, legumes and citrus fruits. It is not a vitamin; "vitamin B8" is a historical name.
- Myo-inositol is not a hormone, stimulant or medicine. It is a food supplement under FSAI and HPRA oversight in Ireland and is not a novel food in the EU.
- D-chiro-inositol was confirmed as not novel in food supplements by the European Commission in 2025.
- Myo-inositol is the most abundant of nine inositol stereoisomers; d-chiro-inositol is a distinct derivative with a different tissue distribution and proposed role.
- The strongest human evidence for myo-inositol is in PCOS: a systematic review by Unfer et al. (Gynecol Endocrinol, 2012, PMID 22296306) of 13 RCTs reported improvements in menstrual regularity, ovulation rate and LH/FSH ratio at 4 g/day.
- Standard capsules provide 500 to 650 mg per capsule at one a day, roughly one-sixth to one-eighth of the researched PCOS dose. Powder is the practical format for gram-level intakes.
- Psychiatric research (panic disorder, OCD, depression) used 12 to 18 g/day, from small trials. Evidence at these doses is preliminary.
- High-dose d-chiro-inositol alone (without the 40:1 myo ratio) has raised concerns about oocyte quality in some research.
- No EU health claim is authorised for inositol under Regulation 1924/2006. Choline, by contrast, holds three authorised claims at 82.5 mg or more per portion.
- Probiotic.ie stocks four inositol capsule products in Dublin: NOW Foods Inositol 500mg, Osavi Inositol 600mg, Swanson Inositol 650mg and NOW Foods Choline & Inositol, compared in the inositol collection.
Frequently Asked Questions — Myo-Inositol Ireland
What is myo-inositol and what does it do?
Is inositol a vitamin? Why is it called vitamin B8?
What is the difference between myo-inositol and d-chiro-inositol?
Does myo-inositol help with PCOS?
What is the correct myo-inositol dosage?
Inositol capsules or powder: which is better?
What are the side effects of inositol supplements?
Can inositol help with anxiety or OCD?
What does choline and inositol do together?
Is inositol legal in Ireland?
Can inositol cause weight gain?
Where can I buy myo-inositol in Ireland?
Related Evidence Guides — Ireland
This guide is for educational purposes only and does not constitute medical advice. The inositol products sold by Probiotic.ie are food supplements regulated under FSAI guidance and are not intended to diagnose, treat, cure or prevent any disease or medical condition. If you have persistent or worsening symptoms, consult a GP or relevant specialist. Always read the label and do not exceed the stated recommended daily dose.
References
- Unfer V et al. Effects of myo-inositol in women with PCOS: a systematic review of randomized controlled trials. Gynecol Endocrinol. 2012;28(7):509-15. PMID 22296306. pubmed.ncbi.nlm.nih.gov/22296306
- Monastra G et al. The sensitivity of the ovary to insulin and androgen production. Gynecol Endocrinol. 2016;32(6):435-8. PMID 26940448. pubmed.ncbi.nlm.nih.gov/26940448
- Barrea L et al. Myo-inositol and d-chiro-inositol in the treatment of PCOS: a guide for the clinician. Expert Rev Endocrinol Metab. 2021;16(3):99-119. PMID 33827343. pubmed.ncbi.nlm.nih.gov/33827343
- Levine J et al. Double-blind, controlled trial of inositol treatment of depression. Am J Psychiatry. 1995;152(5):792-4. PMID 7726322. pubmed.ncbi.nlm.nih.gov/7726322
- Palatnik A et al. Double-blind, controlled, crossover trial of inositol versus fluvoxamine for panic disorder. J Clin Psychopharmacol. 2001;21(3):335-9. PMID 11386498. pubmed.ncbi.nlm.nih.gov/11386498
- Fux M et al. Inositol treatment of obsessive-compulsive disorder. Am J Psychiatry. 1996;153(9):1219-21. PMID 8780431. pubmed.ncbi.nlm.nih.gov/8780431
- Croze ML, Soulage CO. Potential role and therapeutic interests of myo-inositol in metabolic diseases. Biochimie. 2013;95(10):1811-27. PMID 23764390. pubmed.ncbi.nlm.nih.gov/23764390
- European Commission. Novel Food Status Catalogue, entry for d-chiro-inositol (not novel in food supplements), updated 2025. ec.europa.eu novel food catalogue
- European Commission. EU Register on nutrition and health claims: choline entries, Commission Regulation (EU) 432/2012. EU Register (PDF)
- Food Safety Authority of Ireland. Food Supplements Legislation. fsai.ie/legislation/food-legislation/food-supplements