Inositol

A naturally occurring sugar, best known as the supplement taken for irregular cycles.

People take it for

Cycle regularity
Insulin and blood sugar
Testosterone levels
Blood sugar in pregnancy
Cholesterol and blood fats

A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.

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What is inositol?

Inositol is a simple sugar-like compound found in cereals, corn, legumes and meat, and the body makes its own as well, so food covers only part of what it uses. Nine slightly different versions exist, and two of them matter in practice: myo-inositol, much the commonest in food, and D-chiro-inositol, usually sold alongside it in a far smaller amount. Stores sit mainly in the kidneys, brain and liver, where both take part in the messaging cells use to pass a signal inwards. Almost all the research has been done in women, and that is where most of its reputation on the shelf comes from.

Why do people take inositol?

Cycle regularity

The thinking. Periods that come rarely, or stop, are the commonest reason people buy inositol, and it is often started while trying for a baby. The thinking runs through insulin: both inositols act as messengers inside the cell for the insulin signal, and the same messenger family carries hormone signals in the reproductive organs as well.

What research has found. Studies here measured how often periods came and whether ovulation returned. A large comparison of trials found periods came back more often on the two inositols together than on the medicine usually prescribed for the same purpose; in a smaller twelve-week trial, cycles returned in everyone taking myo-inositol who had been having them rarely or not at all. Research here is still young: a few studies so far, mostly pointing the same way.

Insulin and blood sugar

The thinking. Inositol’s reputation is really a reputation about insulin. Reviews describe both forms as insulin-sensitising, and shortfalls of it are described alongside insulin resistance, so people take it when fasting insulin and blood sugar are what they are watching.

What research has found. The clearest evidence is a review of six trials that set myo-inositol against the medicine most often prescribed to women for the same purpose. After a few months, fasting insulin, insulin-resistance scores, testosterone and body mass index all came out much the same on either one, while unwanted effects were reported about five times as often on the medicine. A fair body of trials has looked at this, and most point the same way.

Testosterone levels

The thinking. Raised testosterone is the other thing measured when cycles are irregular, and it is one of the reasons people take inositol. Interest followed the insulin work, so the hormone numbers were measured alongside. Reviewers note that what people actually notice, such as unwanted hair, has been measured far less often than the blood tests.

What research has found. A review pooled nine trials in 440 women and found lower total testosterone, lower free testosterone and more of the protein that carries testosterone in the blood. The reductions were clearest in women of normal weight; among those who were overweight the reviewers found no significant change, and called that part of the analysis exploratory. A reasonable number of trials have measured this, and most of them agree.

Blood sugar in pregnancy

The thinking. Most of the research sits here. Women take myo-inositol through pregnancy, usually from the first weeks and usually because their weight or a family history of diabetes means their blood sugar will be watched; the thinking is the insulin one again.

What research has found. Sixteen studies, ten of them pooling trials, counted how many women went on to have raised blood sugar later in pregnancy. Most found fewer, along with lower readings on the glucose test and fewer early births, in the groups given two grams of myo-inositol twice a day; trials pairing a much smaller dose with D-chiro-inositol found no clear difference. Reviewers rated the certainty low, and nearly every trial was Italian. This is one of the best-studied uses, and several reviews of trials broadly agree.

Cholesterol and blood fats

The thinking. Blood fats are measured at the same visits as insulin and blood sugar, so people taking inositol for one often have an eye on the other. The thinking is that the same chemistry sits behind both, which is why trials in people with metabolic conditions report cholesterol and triglycerides too.

What research has found. One review gathered fourteen trials in adults with metabolic conditions and found lower triglycerides, lower total cholesterol and lower LDL cholesterol, with HDL unchanged. Its authors described the findings in this corner as still contested and asked for more trials. Only a few studies have measured this so far, though they mostly agree.

What does inositol do in the body?

Inositol is a sugar alcohol rather than a vitamin. Some comes from food such as cereals, corn, legumes and meat, and the body makes the rest itself. Cells build it into the fatty molecules of their own membranes, and when a hormone arrives at the surface, small pieces are cut from those molecules and travel inwards as messengers. Passing signals on is the whole of its job.

Insulin is the signal it is best known for: reviews describe myo-inositol and D-chiro-inositol as second messengers in the insulin pathway and as behaving a little like insulin themselves, lowering blood sugar after a meal, which is why the research has followed insulin. The same messengers also carry the signal of other hormones, including the one that drives the thyroid, and take part in cell division and in how the body builds a nervous system in early development. Stores sit mainly in the kidneys, brain and liver, and what is not used leaves in the urine.

What do people say about taking inositol?

These are anecdotes people have shared, not evidence.

What people like

Very commonly, cycles becoming regular and predictable: people describe going from a handful of periods a year to something close to monthly.
Often, ovulation returning and being easier to spot, which is what most were after; several went on to conceive within about six months.
Some mention weight coming off more easily, steadier mood and less tiredness, usually in passing rather than as the reason they started.
A few say it suits them better than the prescription medicine offered for the same thing, which had upset their stomach.

Common complaints

In every thread a few say nothing changed after four to six months, which stings when others in the same thread describe quick results.
Some report the opposite of what they hoped, with cycles stretching to seventy days or more after starting, and stopping it again.
A minority describe putting on weight quickly without eating any differently, and that alone was enough for them to stop taking it.
Very commonly, confusion about the dose and about the ratio of the two forms, with packs listing far less than the research amounts.

How people take it

Four grams a day is the figure quoted most often, usually split into two doses, though some take the lot in the morning.
Powder stirred into water or juice is the usual form; capsules and tablets come up less often, and mainly at smaller doses.
Very commonly it is taken with folic acid, in the same sachet or separately, and often alongside other supplements taken while conceiving.
Most say to give it two to six months before judging it, and several stayed on it into pregnancy once they had conceived.
Some take the two forms together at about forty to one, while others deliberately take myo-inositol alone after reading about the second.

Read from these public discussions:

Myo Inositol - tell me your experiences! (Mumsnet, 2015)
Inositol (myo and or chiro) (Mumsnet, 2021)
MYO inositol? Irregular periods?? HELP! (Mumsnet, 2022)
Myoinositol - did it work for you? (Mumsnet, 2022)
PCOS Myo-Inositol? - Periods have Disappeared (Mumsnet, 2022)
Myo inositol or myo /d chiro for pcos (Mumsnet, 2023)

What forms of inositol are there?

Form	What’s different	Per serving, on products we list
Myo-inositol	The form that is commonest in food and in the body, and the one nearly every trial used.	500 mg
D-chiro-inositol	A closely related form of the same sugar, usually sold in a much smaller amount beside myo-inositol.	not in our price tables yet

What else is worth knowing about inositol?

Labels give the inositol per serving, and a serving may be more than one capsule or scoop; most trials used two grams of myo-inositol twice a day.
Many products pair the two forms at about forty parts myo-inositol to one of D-chiro-inositol, the ratio one trial reported ovulation most often on.
In one review, unwanted effects were about five times as common on the prescribed medicine as on myo-inositol; in another, one woman reported headaches.
Nearly all of this research is in women, and much of it in pregnancy; one review describes myo-inositol as appearing safe in human pregnancy.

If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.

The research behind this page (28 studies)

How much does inositol cost?

That depends on the form and the pack, so we work out the price of the same dose of every inositol product we can find and rank them.

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