Most PCOS supplement advice starts and ends with inositol, and that’s roughly right — it’s the one with the strongest evidence behind it. What almost nobody tells you is the dose. The labels say 2,000mg. The trials used 4,000mg.
That gap changes everything about which product to buy, because at the real dose a cheap bottle of capsules stops being cheap. Below: what the research actually supports, what it costs per day at the proper dose, and the two products sold here that look like bargains and aren’t.
What is PCOS?
Polycystic Ovary Syndrome, better known as PCOS, is a hormonal disorder that affects the ovaries. Typical symptoms include polycystic ovaries, irregular periods and elevated androgen levels.
The main driver of PCOS is insulin resistance. Studies show that more than half of people with PCOS suffer from insulin resistance. This is where the body’s cells respond poorly to insulin, resulting in excessive androgen production by the ovaries. The excessive androgen production leads to problems with reproduction and fertility.
That’s where inositol comes in. It’s a sugar-like compound your body makes naturally, and it acts as a messenger inside cells — including the ones that respond to insulin. Supplementing it improves how well those cells hear the insulin signal, which is why it’s the most-studied supplement in PCOS.
There are two forms that matter, myo-inositol and D-chiro-inositol, and the ratio between them turns out to be as important as the dose.
Inositol Dose for PCOS
Most bottles suggest 2,000mg of myo-inositol a day. The clinical regimen is 4,000mg, usually split 2,000mg morning and 2,000mg evening.
That’s the dose used in the trials on insulin resistance and ovulation, and it’s the single most common reason inositol appears not to work — people take half of what was studied and conclude it isn’t for them.
How much inositol should I take for PCOS?
The standard protocol is:
- 4,000mg myo-inositol daily, split into two 2,000mg doses
- 100mg D-chiro-inositol daily, which comes with it in any 40:1 product
- Taken with food, morning and evening
- For at least three months before judging whether it’s working
Some protocols go higher for specific situations, but 4,000mg is the figure almost all the PCOS research is built on. Going above it hasn’t been shown to help more, and inositol is water-soluble, so the excess is simply excreted.
If you’re only taking 2,000mg because that’s what the label says, you’re taking a half dose. That’s the most common mistake with this supplement.
Why the 40:1 ratio matters
Myo-inositol and D-chiro-inositol are two forms of the same compound, and they do different jobs. Myo-inositol handles glucose uptake and the signalling that lets a follicle mature. D-chiro-inositol is involved in glycogen storage and in androgen production.
Healthy ovarian follicular fluid contains roughly 40 parts myo to 1 part D-chiro. Products are formulated to match that because tipping the balance the other way is actively unhelpful — trials using high D-chiro found egg quality got worse, not better. More is not better with this one, and the ratio does more work than the total.
The practical upshot: buy a product already formulated at 40:1 and you never have to think about it. All three below are.
Three practical notes:
- Give it three months. Inositol works on insulin sensitivity, which shifts slowly. Cycle changes typically show up somewhere between the second and third month.
- Split the dose. Two 2,000mg servings rather than one 4,000mg hit — better tolerated and closer to how it was studied.
- Powder is easier at this dose. 4,000mg is eight 500mg capsules. See the section below on why that matters.
PCOS Supplements to Regulate Periods
Irregular or missing periods are usually what sends someone looking for a PCOS supplement in the first place. So it helps to understand what’s actually going wrong.
Insulin resistance pushes the ovaries to produce more androgens. High androgens interfere with follicle development. And a follicle that never matures never releases an egg, which is why the period doesn’t arrive. The cycle isn’t late so much as it never got started.
Inositol works at the top of that chain rather than the bottom. It won’t bring on a period the way a hormonal treatment does. What it does is improve insulin sensitivity, which brings androgens down, which lets follicles develop the way they should. When it works, the cycle returns on its own.
Most of the trials showing restored ovulation ran three to six months at 4,000mg daily, and cycles usually start shifting around month two or three. If nothing has changed by month four, that’s worth a conversation rather than a higher dose. Insulin resistance drives most PCOS, but not all of it, and a supplement won’t fix a problem it isn’t aimed at.
One last thing. If you’re on the combined pill for cycle control, the bleed you get each month isn’t a real period, and inositol won’t change it. It may still be worth taking for the insulin resistance underneath, but your cycle won’t tell you whether it’s working.
So which product gets you there?
Best PCOS Supplement
Three worth knowing about: one prescription-only, one on the shelf at Watsons, one you order in.
1. Revosit
Revosit is what most fertility clinics reach for first, and it’s prescription-only. Each daily dose gives you 4,000mg of myo-inositol and 100mg of D-chiro-inositol — the full clinical dose, in the 40:1 ratio, with nothing you need to calculate.
That’s the case for it. You don’t have to work out servings, you don’t have to double anything, and a doctor is overseeing it. The case against is that you can’t just buy it, and it costs more than the retail options.
- Pros: Full 4,000mg dose in one serving. Prescribed and supervised.
- Cons: Prescription-only, so it needs a consultation. Most expensive per day.
2. Moom Health Happy Hormones
Shelf price when photographed in December 2025: S$39.90. Watsons currently sells it at S$27.93.
Moom is the easiest to actually buy — it’s on the shelf at Watsons, currently S$27.93 for 30 sachets, and it comes in lemon and passion fruit, which matters more than it sounds when you’re taking something daily for months.
Here’s the part to watch. Each sachet contains 2,000mg of myo-inositol and 50mg of D-chiro, and the directions say one sachet daily. That’s exactly half the clinical dose. To reach 4,000mg you need two sachets a day, which means a box lasts fifteen days, not thirty, and the real cost is closer to S$56 a month.
Worth reading the ingredient list too: alongside the inositol there’s lemon and ginger extract, licorice, sweeteners and a small amount of brown sugar. The quantities are small, but it’s worth knowing if you’re taking this specifically for insulin resistance.
- Pros: Available at Watsons, no ordering or shipping. Flavoured, which helps with long-term adherence. Vegan and halal certified.
- Cons: One sachet is half the studied dose. At two a day the cost roughly doubles. Contains sweeteners and brown sugar.
3. Ovasitol
Ovasitol is the one the research community actually uses, and it’s made by Theralogix, a practitioner-channel brand. It’s the only 40:1 inositol supplement independently tested and certified by NSF International — meaning someone outside the company has verified the bottle contains what the label says.
The formula is pure inositol and nothing else. No flavouring, no sweeteners, no fillers. Two doses a day gives you the full 4,000mg plus 100mg of D-chiro, and a 90-day supply is 180 servings, so the maths is done for you.
It comes as a canister with a scoop or as single-serve packets. The packets cost slightly more and are easier to travel with; otherwise there’s no difference.
- Pros: NSF certified for content and purity, which nothing else here is. Pure inositol, no additives. Unflavoured, so it mixes into anything. Vegan and gluten-free. Cheapest per day at the full 4,000mg dose.
- Cons: Not sold locally, so you’re ordering internationally. Unflavoured means it tastes of nothing, which some people dislike more than a flavour they don’t love.
Why Cheap Capsule Inositol Isn't Cheap
Two capsule products sold in Singapore look much cheaper than Moom: Wholesome Story and Nano Singapore. Both get the 40:1 ratio right. The catch is the capsule.
Only about 500mg of inositol fits in one capsule (magnesium has the same problem), so a 4,000mg day means eight capsules. A “serving” on the label is whatever the brand decides it is, not the dose the research used.
Nano Singapore lists a serving as 2 capsules: 1,000mg of myo-inositol, a quarter of the studied dose (label above).
Wholesome Story lists 4 capsules: 2,000mg, half the studied dose (label above).
At the full 4,000mg, a 120-capsule bottle of either lasts 15 days, and the bargain disappears. Here is what each option costs per day at the dose the trials used:
| Product | Form | Pack price | For 4,000mg a day | Cost per day |
|---|---|---|---|---|
| Ovasitol (canister) | Powder | S$139.56 for 180 scoops | 2 scoops | S$1.55 |
| Moom Happy Hormones | Sachet | S$27.93 for 30 sachets | 2 sachets | S$1.86 |
| Ovasitol (packets) | Powder | S$176.18 for 180 packets | 2 packets | S$1.96 |
| Wholesome Story | Capsule | S$35.07 for 120 capsules | 8 capsules | S$2.34 |
| Nano Singapore | Capsule | S$38.90 for 120 capsules | 8 capsules | S$2.59 |
| Revosit (prescription only) | Sachet | S$64.90 for 30 sachets | 2 sachets | S$4.33 |
Prices checked December 2025, except Moom (Watsons, September 2026). Check before you buy.
NAC for PCOS
Inositol and NAC both work on insulin resistance, but they get there differently. Inositol improves how insulin receptors function. NAC works on the oxidative stress and inflammation that impaired those receptors in the first place.
That’s why they stack rather than compete. If inositol alone hasn’t moved things after three months, NAC is the reasonable next addition rather than a replacement.
The evidence goes back further than most people realise. A 2002 trial found NAC improved insulin sensitivity in women with PCOS, and it’s been studied since against metformin — the standard pharmaceutical for the same problem. Results have been broadly comparable in several trials, with fewer gastrointestinal side effects, though metformin has far more data behind it and NAC is not a substitute for a prescription your doctor has made.
Dose: 600 to 1,800mg daily, usually split across meals. Same range used for fertility generally.
We’ve covered NAC in full — including what it does for endometriosis, fibroids and egg quality — in our guide to NAC for women.
Best Supplement Stack for PCOS
So what does a full stack actually look like? Inositol is the base, but it isn’t the whole answer, and the rest depends on what you’re treating.
- Inositol, 4,000mg daily — the foundation. Works on insulin sensitivity, which is the mechanism underneath most PCOS symptoms. Split morning and evening, in the 40:1 myo to D-chiro ratio.
- NAC, 600–1,800mg daily — the second layer. Addresses the same insulin resistance by a different route, through oxidative stress rather than receptor function. Worth adding if inositol alone hasn’t shifted things after three months.
- Vitamin D, if you’re deficient — worth testing before supplementing rather than adding it blindly. Deficiency is common in PCOS and it affects insulin sensitivity.
- Omega-3 — for the inflammatory component. Modest effects, but low risk and cheap.
- CoQ10, if you’re trying to conceive — works on egg quality specifically rather than on PCOS itself. See our CoQ10 guide for dosing.
The table below sets out the doses. For prices, see the inositol table above and our NAC and CoQ10 comparisons.
| Supplement | Daily dose | What it’s for |
|---|---|---|
| Inositol (40:1 myo to D-chiro) | 4,000mg myo-inositol + 100mg D-chiro, split morning and evening | Insulin sensitivity. The base of the stack. |
| NAC | 600–1,800mg, split across meals | The same insulin resistance by a different route. Add it if inositol alone hasn’t shifted things after three months. |
| Vitamin D | Only if a blood test shows you’re low, dosed to the result | Deficiency is common in PCOS and affects insulin sensitivity. |
| Omega-3 | Standard label dose | The inflammatory side. Modest effect, low risk. |
| CoQ10, if trying to conceive | 400–600mg ubiquinone, or 200–300mg ubiquinol | Egg quality, not PCOS itself. |
FAQs
What's the best inositol dose for PCOS?
4,000mg of myo-inositol daily, split morning and evening, plus 100mg of D-chiro in the 40:1 ratio. Most labels say 2,000mg, which is half the studied dose.
Inositol or metformin for PCOS?
Trials comparing them have found broadly similar effects on insulin sensitivity and ovulation, with fewer gastrointestinal side effects from inositol. Metformin has far more data behind it. If your doctor has prescribed it, inositol isn’t a replacement.
Does NAC help PCOS?
It works on the same insulin resistance by a different route — through oxidative stress rather than receptor function. Reasonable to add if inositol alone hasn’t shifted things after three months.
Best PCOS supplement to regulate periods?
Inositol at 4,000mg daily. It doesn’t induce a period; it improves insulin sensitivity so ovulation resumes on its own. Expect two to three months.
Who Am I?
Dr. Mark Chern (Ph. D) is a Chinese Medicine practitioner in Singapore, trained in Taipei and active in women’s health since 2011. With over a decade of expertise in treating fertility, pregnancy and various women’s health conditions, Dr Mark is always faced with questions about supplements for fertility and hormone regulation.
He has researched deeply into melatonin, CoQ10 and NAC for fertility also. This article covers what the research shows about inositol for PCOS — the dose, the 40:1 ratio, and which products actually get you there.
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