Myo-Inositol Supplement Ireland: Evidence Guide, PCOS, Dosage & Where to Buy
Myo-inositol is a naturally occurring B-vitamin family nutrient 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, and what to expect from a supplement at typical doses.
Myo-inositol is a naturally occurring carbohydrate belonging to the vitamin B-complex family, found in grains, legumes, and fruit. It is the most biologically abundant of nine inositol stereoisomers and functions as a second messenger in insulin signalling pathways.
In Ireland, myo-inositol supplements are classified as food supplements regulated by the FSAI — they are not medicines, carry no authorised EU health claims under EC Regulation 1924/2006, and are subject to Irish VAT at 13.5%.
The strongest human evidence signal 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 doses of 500 mg–2 g/day (standard supplement range), the evidence for specific effects in healthy adults is limited. Clinical psychiatric research used 12–18 g/day — well above typical supplement doses.
What has not been proven: inositol has not been established as a treatment for PCOS, anxiety, OCD, or any other medical condition. It is not interchangeable with d-chiro-inositol, and high-dose d-chiro-inositol supplementation alone has raised concerns about egg quality in some research.
NOW Foods Inositol 500mg (100 veg caps, €17.45) and NOW Foods Choline & Inositol (100 veg caps, €17.95) are available from Probiotic.ie with nationwide tracked delivery from Dublin.
- 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, solo inositol vs choline & inositol combo
- 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 classified within the B-vitamin family, synthesised endogenously from glucose-6-phosphate in the kidneys and liver, and found exogenously in grains, legumes, citrus fruits, and nuts — with highest concentrations in the brain, testes, and skeletal muscle.
A myo-inositol supplement in Ireland is a food supplement providing isolated myo-inositol — typically in capsule or powder form — and is regulated by the FSAI as a food supplement, not a medicine. It is not a hormone, not a drug, and carries no authorised EU health claims. The compound is found naturally in food and is also produced endogenously by the human body. The most studied use case is in women with PCOS, where systematic reviews suggest a potential supportive role in hormonal and metabolic markers — though inositol is not an approved PCOS treatment. NOW Foods Inositol 500mg provides 500 mg of myo-inositol per veg capsule, produced in a GMP-certified facility, and is available from Probiotic.ie at €17.45 for 100 capsules, with tracked delivery across Ireland.
- What it is: A naturally occurring cyclic polyol in the B-vitamin family; produced endogenously from glucose-6-phosphate
- Most abundant form: Myo-inositol — the primary isomer found in human tissue and in food
- Dietary sources: Wholegrains, legumes (beans, lentils), citrus fruits, nuts, cantaloupe — typically 1–2 g/day from a varied diet
- Supplement source: Typically produced via fermentation of phytic acid (inositol hexaphosphate) from plant sources — suitable for vegans
- Endogenous production: The kidneys produce approximately 2 g of inositol per day from glucose-6-phosphate
- Clinical trial dose range: 2–4 g/day in PCOS research; 12–18 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
- Vegetarian/vegan suitable? Yes — NOW Foods Inositol 500mg uses hypromellose (cellulose) capsules with no animal ingredients
- Irish regulatory status: Food supplement under FSAI guidelines — not a medicine; no disease treatment claims permitted
- Irish VAT rate on supplements: 13.5%
- 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–2 g/day is not the dose used in psychiatric research — psychiatric trials used 12–18 g/day
- Myo-inositol is not a stimulant, fat burner, or weight-loss supplement — no established evidence for weight loss in healthy populations
- Myo-inositol supplements do not carry any authorised EU health claim under EC Regulation 1924/2006
What is well-supported: Improvements in menstrual regularity, ovulation rate, and hormonal markers (LH/FSH ratio, androgens) in women with PCOS — 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 in healthy populations. Psychiatric research used doses (12–18 g/day) dramatically higher than standard supplements. Evidence outside PCOS is preliminary.
Most relevant human dose range: 2–4 g/day in PCOS studies; 500 mg–1 g/day in standard supplement format.
Key safety note: High-dose d-chiro-inositol alone may negatively affect oocyte quality. 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 | 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 side effects and safety
- Choline and inositol: the combination supplement
- Inositol supplements in Ireland: regulation 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 different 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 is often grouped with the B-vitamin family because of its structural similarity to B vitamins and its involvement in cell signalling — though it is not a vitamin in the strict sense, as the human body synthesises it endogenously from glucose-6-phosphate, primarily in the kidneys and liver at approximately 2 g per day.
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 specifically, 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 regulated under FSAI guidelines and EC Directive 2002/46/EC. It is not a medicine. No EU health claim is authorised for inositol under EC 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 it is 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, which are derived from inositol, appear to play a mediating role in how cells respond to insulin.[7]
The key systematic review in this area was conducted by Unfer et al. from Università di Roma and published in Gynecological Endocrinology in 2012 (PMID 22296306). The review 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 to placebo or metformin.[1]
A subsequent review and clinical guidance paper by Barrea et al. (Expert Reviews in Endocrinology & Metabolism, 2021, PMID 33827343) outlined the clinical evidence base and proposed that myo-inositol, particularly in combination 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 appropriate 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 NOW Foods Inositol 500mg or NOW Foods Choline & Inositol produce these effects. These products are food supplements, not medicines. No authorised EU health claim is currently made for inositol on this page or on the products.
NOW Foods Inositol 500mg — 100 Veg Capsules
Pure myo-inositol, vegan capsules, GMP-certified facility. Tracked 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 for other areas.
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 mg/day | 1 capsule (NOW Inositol 500mg, label dose) | Nutritional supplement — general use | Below all clinical trial doses; no specific evidence at this level |
| 2 g/day | 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 systematic review | RCT Systematic Review (13 trials); consult GP required |
| 12–18 g/day | Powder only — not practical in capsule form | Psychiatric research only (depression, panic, OCD) | Small early-stage trials (n=13–20); not recommended without specialist supervision |
The suggested use on NOW Foods Inositol 500mg is one capsule daily with food — 500 mg. This is the label dose and is well below any dose 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, and would typically use an inositol powder for practical dosing at that level.
Early psychiatric research — Levine et al. (Am J Psychiatry, 1995, PMID 7726322) and Palatnik et al. (J Clin Psychopharmacol, 2001, PMID 11386498) — explored inositol at 12–18 g/day in depression, panic disorder, and OCD in small trials (n=13–20). Results were mixed: the panic disorder crossover showed significant reduction in attack frequency vs fluvoxamine; the depression data was inconsistent across studies. These are hypothesis-generating findings, not practice-changing ones. The dose used (12–18 g/day) is 24–36× higher than a standard 500 mg capsule. Anxiety, OCD, and depression require professional diagnosis and management — they should not be self-treated with supplements. For supplements 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–2 g/day), myo-inositol is generally considered well tolerated. The most commonly reported side effects — reported in high-dose psychiatric research — are gastrointestinal, including nausea, flatulence, and loose stools. These effects are dose-dependent and have been primarily observed 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 a compound found naturally in food and produced endogenously — the body has established pathways for handling it.
Key cautions to be aware of: 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 — always consult a GP before use. Drug interactions: no significant pharmacokinetic interactions have been established, but those on insulin sensitisers (including metformin, used in PCOS) 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 (12–18 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 both members of the B-vitamin family with overlapping roles in phospholipid metabolism. Both are components of key membrane phospholipids — phosphatidylcholine and phosphatidylinositol — which is the rationale for combining them in supplement form.
Choline is an essential nutrient with EFSA-authorised health claims including support for normal lipid metabolism and normal liver function, at a reference intake of 400 mg/day for adults. Inositol does not carry an authorised EFSA health claim. Combining them in a supplement does not create new evidence for the combination — each ingredient has its own evidence profile.
NOW Foods Choline & Inositol provides 250 mg of choline (as choline bitartrate) and 250 mg of inositol per capsule — a practical option for those who want both compounds in one daily capsule, at a lower inositol dose than the solo product. The choline component contributes toward the EFSA reference intake of 400 mg/day alongside dietary sources.
| Comparison | NOW Inositol 500mg | NOW Choline & Inositol |
|---|---|---|
| Inositol per capsule | 500 mg | 250 mg |
| Choline per capsule | None | 250 mg (as Choline Bitartrate) |
| Capsule count | 100 | 100 |
| Price | €17.45 | €17.95 |
| Best suited for | Those wanting higher inositol dose | Those wanting both compounds together |
| Vegan | Yes | Yes |
| GMP certified | Yes | Yes |
Choose the Inositol 500mg if your primary interest is a higher per-capsule inositol dose. Choose Choline & Inositol if you want both nutrients in one capsule at a combined entry dose. Neither product replaces medical advice or dietary assessment.
Inositol Supplements in Ireland: Regulation and Where to Buy
In Ireland, myo-inositol supplements are classified as food supplements regulated by the Food Safety Authority of Ireland (FSAI) under EC Directive 2002/46/EC. They are not medicines, carry no authorised health claims under EC 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, purchasing directly from the manufacturer. Both inositol products are dispatched from Dublin with tracked delivery across Ireland — next-day via DPD on orders placed before the daily cut-off, free on orders over €75. UK customers should visit probiotic.co.uk.
Product details on this page — including dose (500 mg per capsule for NOW Inositol; 250 mg inositol + 250 mg choline per capsule for NOW Choline & Inositol), capsule count (100 per bottle), and prices (€17.45 and €17.95 inc. VAT at 13.5%) — were verified by Probiotic.ie from current NOW Foods packaging and supplier information. Product details should always be checked against the current label before use, as formulations and pricing may change.
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 NOW Foods Inositol 500mg or NOW Foods Choline & Inositol produce these effects. These products are food supplements, not medicines. No authorised EU health claim is currently made for inositol on this page or on the products.
Both NOW Foods Inositol Products — Available from Probiotic.ie
Authorised Irish retailer for NOW Foods. Tracked delivery from Dublin. Free over €75.
- Myo-inositol is a naturally occurring cyclic polyol classified in the B-vitamin family, produced endogenously at approximately 2 g/day and found in grains, legumes, and citrus fruits.
- Myo-inositol is not a hormone, stimulant, or medicine — it is a food supplement regulated by the FSAI in Ireland.
- Myo-inositol is the most biologically 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.
- Most PCOS trials used 4 g/day of myo-inositol — standard 500 mg capsule supplements at one capsule per day provide considerably less than the researched dose.
- Psychiatric research (panic disorder, OCD, depression) used 12–18 g/day — well above supplement doses. Evidence at these levels is preliminary and from small trials.
- High-dose d-chiro-inositol alone (without maintaining the 40:1 myo ratio) has raised concerns in some research about oocyte quality — relevant for those pursuing fertility support.
- No EFSA-authorised health claim currently exists for myo-inositol under EC Regulation 1924/2006.
- In Ireland, inositol supplements are regulated by the FSAI as food supplements — not medicines. Irish VAT at 13.5% applies.
- NOW Foods Inositol 500mg (100 veg caps, €17.45) and NOW Foods Choline & Inositol (100 veg caps, €17.95) are available from Probiotic.ie with nationwide tracked delivery from Dublin.
Frequently Asked Questions — Myo-Inositol Ireland
What is myo-inositol and what does it do?
What is the difference between myo-inositol and d-chiro-inositol?
Does myo-inositol help with PCOS?
What is the correct myo-inositol dosage?
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. NOW Foods Inositol 500mg and NOW Foods Choline & Inositol are food supplements regulated under FSAI guidelines 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. Probiotic.ie is regulated under FSAI food supplement guidelines. 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
- Food Safety Authority of Ireland. Food Supplements Legislation. FSAI.ie. 2024. — fsai.ie/legislation/food-legislation/food-supplements