Metformin can modestly reduce facial hair growth, but it won’t stop it completely. In clinical trials, women with PCOS who took metformin saw their hirsutism scores drop by about 15 to 20 percent over six to twelve months. That’s a noticeable improvement, but it’s milder than what other medications can achieve, and it works slowly.
How Metformin Affects Facial Hair
Metformin wasn’t designed to treat excess hair. It’s a blood sugar medication that happens to have a useful side effect: it lowers insulin levels, which in turn reduces the amount of testosterone your body produces. In women with PCOS, high insulin drives the ovaries to pump out extra androgens (male-type hormones), and those androgens are what transform fine facial hair into thicker, darker, more visible growth. By interrupting that chain at the insulin level, metformin gradually lowers the hormonal signal that fuels unwanted hair.
This indirect approach is both metformin’s strength and its limitation. It addresses one of the root drivers of excess hair rather than just blocking the hormone at the skin. But because it works upstream of the hair follicle itself, the effect on visible hair is slower and less dramatic than medications that directly block androgens.
What the Clinical Numbers Show
Researchers measure excess hair using the Ferriman-Gallwey score, which rates hair thickness and coverage across nine body areas on a scale from 0 to 36. In one controlled trial, women taking metformin saw their scores drop from 13.0 to 10.4 over 12 months, a statistically significant change. In the placebo group, scores barely moved.
A separate study tracking women over six months found metformin reduced hirsutism scores from 12.5 to 10.0. Hair growth velocity, measured in millimeters per day, also slowed during metformin treatment compared to placebo (0.67 mm/day versus 0.77 mm/day). These differences are real but subtle. Most women notice some thinning and slower regrowth rather than hair disappearing entirely.
One important caveat: metformin does not reverse terminal hairs that have already established themselves. Once a hair follicle has been converted from fine vellus hair to thick terminal hair by years of androgen exposure, lowering androgens can slow its growth and sometimes thin it, but the follicle itself doesn’t revert. For hair that’s already coarse and deeply rooted, physical removal methods like laser hair removal or electrolysis are more effective at producing visible results.
How It Compares to Other Treatments
When researchers directly compared metformin to spironolactone (an androgen blocker commonly prescribed for facial hair), spironolactone came out ahead. Over six months, spironolactone reduced hirsutism scores from 12.9 to 8.7, while metformin brought scores from 12.5 down to 10.0. Spironolactone also worked faster, showing significant improvement by three months, while metformin’s testosterone-lowering effect took closer to six months to fully kick in.
Combined oral contraceptive pills also outperform metformin for hirsutism on their own. The 2023 international evidence-based guidelines for PCOS recommend oral contraceptives over metformin as first-line treatment when the primary concern is excess hair growth and irregular periods. Metformin is preferred for metabolic issues like insulin resistance and is recommended over supplements like inositol for hirsutism, but it sits behind other options in the hair-specific pecking order.
Where metformin may add the most value for facial hair is in combination. A Cochrane review found that combining metformin with an oral contraceptive pill improved hirsutism more than either medication alone. If you’re already on birth control for PCOS and still dealing with unwanted hair, adding metformin may provide incremental benefit beyond what the pill achieves by itself.
How Long Before You See Results
Patience is essential. Hair follicles cycle through growth phases that last weeks to months, so even after your androgen levels drop, existing hairs need to finish their current growth cycle before you notice a change. Most trials measuring hirsutism improvements with metformin show statistically meaningful changes at six months, with continued improvement through twelve months. Don’t expect to see results at four or eight weeks.
In one 14-month crossover study, women completed a full six-month phase of metformin before hirsutism scores and self-assessed hair growth showed significant improvement compared to placebo. That timeline aligns with the biology: it takes time for lower androgen levels to translate into visibly thinner, slower-growing hair.
What Metformin Can and Can’t Do
Metformin is best understood as one piece of a larger strategy rather than a standalone solution for facial hair. Here’s what to realistically expect:
- It can slow the rate of new hair growth and reduce hair thickness over several months
- It can lower the testosterone levels driving excess hair, particularly when high insulin is a major factor
- It can’t eliminate established coarse facial hair on its own
- It can’t work as quickly or as powerfully as direct androgen blockers or cosmetic procedures
For women with PCOS whose primary frustration is facial hair, metformin alone is unlikely to be satisfying as the sole treatment. Its real strength lies in improving insulin sensitivity and metabolic health, with a moderate hair benefit as a bonus. Combining it with an oral contraceptive, an androgen blocker, or hair removal methods like laser treatment typically produces better cosmetic results than relying on metformin by itself.