Does Inositol Work as Well as Metformin for PCOS? What a Head-to-Head Trial Found
A 192-woman trial compared inositol, metformin, diet, and all three for PCOS. What it found for cycles and insulin, and what it can't tell you.
Photo: Iskender Galat / Unsplash
First, I have some happy news to share! Last spring, PCOS was officially renamed PMOS (polyendocrine metabolic ovarian syndrome) in recognition of how it has body-wide effects and can be present even without ovarian cysts. Not everyone has fully adopted the new name, so you will likely still run into "PCOS" pretty often. So back to the question: does inositol work as well as metformin in PMOS? In a 2026 randomized trial of 192 women, more women taking inositol reported regular cycles after 12 weeks than women taking metformin: 64.6 percent compared with 39.6 percent, so roughly two in three women against four in ten. A calorie-restricted diet on its own reached 72.9 percent, about three in four, and all three together reached 85.4 percent, more than four in five. Reviews that pooled earlier trials found inositol and metformin closer to even, which is why this trial is one data point rather than a final answer.
PMOS is a hormonal condition in which ovulation is irregular, androgens (hormones like testosterone) tend to run high, and insulin resistance is common. Insulin resistance means your cells respond less to insulin, so your body has to make more of it to keep blood sugar in range. That is why a diabetes medication and a supplement that works on insulin signaling both come up when you're looking at PMOS options.
What the trial compared
Irfan and colleagues randomly assigned 192 women aged 18 to 35 to one of four groups for 12 weeks. One group took metformin. One took inositol, a combination of myo-inositol and D-chiro-inositol given twice a day at a ratio of 40 to 1. One followed a calorie-restricted diet of 1,200 to 1,500 calories a day, and the last group did all three.
The main outcomes included body mass index (BMI) and HOMA-IR (homeostatic model assessment of insulin resistance), a score calculated from fasting glucose and fasting insulin that estimates how insulin resistant someone is. The secondary outcomes included testosterone, cycle regularity, and the ratio between luteinizing hormone (LH) and follicle-stimulating hormone (FSH), two hormones made by the pituitary gland at the base of the brain that help control ovulation.
Every group improved. The combination produced the largest drops in both HOMA-IR and BMI. For cycles, the order was combination first, then diet, then inositol, then metformin, and the difference across the four groups was statistically significant, meaning it was unlikely to be due to chance alone. The authors wrote that, given the short follow-up, these findings reflect "early improvements rather than sustained normalisation."
The diet-only group also did better on cycles than metformin
It would be easy to read this trial as "supplement beats drug." The diet-only group also did better on cycles than the metformin group, though, and the combination did better than everything. I read that as three approaches that add to each other rather than a contest between a supplement and a drug, though the trial wasn't designed to measure how much each one adds. That fits how I think about PMOS in clinic: insulin resistance has several inputs, so working on more than one of them at a time usually helps more than relying on a single tool.
Inositol isn't a new idea in PMOS. I use it frequently with patients, and Dr. Joyce made a great video on why it is one of the better-researched supplements for PMOS. The 2024 guideline review below rates the evidence more cautiously than that video did, and I keep that in mind. In the same video, she explained that the two forms do different jobs. Myo-inositol is involved in FSH signaling in the ovary, which affects cycle regularity and egg quality, and it makes up the large majority of the inositol in the ovary. D-chiro-inositol is more involved in blood sugar handling. That is why the trial's combination, weighted heavily toward myo-inositol, makes sense to me.
What this trial can't tell you
There was no placebo group, meaning no group took a dummy treatment for comparison. A diet can't be hidden from the person following it, so the women in the two diet groups knew which treatment they were getting. Cycle regularity was based on what participants reported, and that is the kind of outcome where expectations can shift the result.
Twelve weeks is also short. Three months covers only a few cycles, and the authors themselves called these early improvements. The trial enrolled only women aged 18 to 35, and all three researchers were based at two medical colleges in Islamabad, Pakistan, so whether the same pattern holds for older women, or in other populations, is still an open question.
How it fits with earlier research
A 2023 meta-analysis from Semmelweis University in Budapest pooled 26 randomized trials covering 1,691 women. Women taking inositol were 1.79 times as likely as those on placebo to have a regular cycle, and inositol was non-inferior to metformin for cycle regularity, meaning it did at least about as well.
A 2024 review, carried out to inform the 2023 international PCOS guidelines, gathered 30 trials with 2,230 participants and reached a more cautious conclusion. Those authors described the evidence for inositol in PMOS as limited and inconclusive. They found likely no difference between inositol and metformin for reproductive outcomes, and they found that metformin may do better for waist-to-hip ratio and hirsutism (excess hair growth). They also found that myo-inositol likely causes fewer digestive side effects than metformin, though these are typically mild and tend to settle on their own. Their advice was shared decision-making between patients and clinicians, weighing that uncertainty against personal values and preferences.
Taken together, the two earlier reviews put inositol and metformin roughly even on cycles and reproductive outcomes. The 2026 trial found a bigger difference in inositol's favor, and a single 12-week trial with no placebo group isn't enough to overturn that. It does add a direct comparison against diet, which is the kind of head-to-head evidence the trial's own authors describe as limited.
Questions to bring to your prescriber
If you take metformin, please don't stop it on the strength of this trial. It is a prescription medication, and changes belong with whoever prescribes it. This trial is still a useful thing to bring to that appointment. You might ask whether inositol could be added alongside your current plan, whether structured diet support is part of that plan, and how you'll both measure progress, whether that is cycle tracking, fasting insulin, or something else.
If your blood sugar markers look normal, including your A1c (an estimate of your average blood sugar over the past two to three months), but you still suspect insulin resistance, the post on a normal A1c with high fasting insulin explains which test can show your body making extra insulin to keep blood sugar in range. For the broader picture of what helps insulin resistance, there is a separate post on where the evidence for reversing insulin resistance is strongest, and the diabetes and metabolic health hub gathers the rest.
If you want a more structured approach to metabolic health, the Wayfinder's Well membership includes the full educational library, and Beyond Blood Sugar, an upcoming course on diabetes, will arrive in three parts.
FAQ
Is inositol better than metformin for PMOS?
In one 2026 trial of 192 women, more women in the inositol group reported regular cycles after 12 weeks than in the metformin group, 64.6 percent compared with 39.6 percent, roughly two in three against four in ten. A 2023 review that pooled earlier trials found inositol did at least about as well as metformin for cycle regularity. So inositol looks at least comparable on cycles, and one trial isn't enough to call it better.
What is the difference between myo-inositol and D-chiro-inositol?
Both are forms of inositol, a compound your body uses in insulin and hormone signaling. Myo-inositol is involved in FSH signaling in the ovary, which affects ovulation and cycle regularity. D-chiro-inositol is more involved in blood sugar handling. The 2026 trial gave the two together at a ratio of 40 parts myo-inositol to 1 part D-chiro-inositol.
Can I stop metformin and take inositol instead?
That is a decision for the clinician who prescribes your metformin, and it isn't one to make on your own. The 2026 trial compared each approach in separate groups of women over 12 weeks. It didn't test switching from one to the other, which leaves what happens after a switch unmeasured.
Does diet help PMOS as much as medication?
In the 2026 trial, a calorie-restricted diet on its own led to more women reporting regular cycles than metformin did, 72.9 percent compared with 39.6 percent, about three in four against four in ten. Diet, inositol, and metformin together did best of all. The trial had no placebo group and lasted 12 weeks, so these are early results.
How long does inositol take to work for PMOS?
The 2026 trial measured results at 12 weeks, and the authors described the changes they saw as "early improvements rather than sustained normalisation." Whether the effect holds over a longer stretch wasn't tested in that trial.
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