Encyclopedia · drug with hair side effects
Metformin
The world's most-used diabetes pill woke sleeping hair follicles in mice and was linked to regrowth in 6 of 12 women with a scarring alopecia, but there is no randomized hair trial and it is not a baldness treatment.
What it is
A prescription medicine for type 2 diabetes and PCOS, prescription-only in the US, EU and UK. Any hair use is off-label.
How it works
Metformin activates AMPK and autophagy. In mice, autophagy-activating molecules including metformin and rapamycin pushed follicles from rest into growth. Chai 2019 In scalp from scarring alopecia, metformin reversed fibrosis and Th17 gene signatures. Bao 2024
What the studies show
- Metformin, rapamycin and alpha-ketoglutarate induced growth from rest in mice, and autophagy blockers cancelled it. Mice only. Chai 2019
- In 12 patients with central centrifugal cicatricial alopecia given extended-release metformin 500 mg daily, 9 improved (pain, inflammation, itch) and 6 showed regrowth after at least 6 months. It was uncontrolled, and author disclosures include industry fees. Bao 2024
- A metformin nanosheet beat topical minoxidil in a mouse model of pattern hair loss with fewer side effects. Mice only. Mai 2025
- A phase 1 trial of topical pentoxifylline/metformin in alopecia areata (NCT06087796, 60 people) is registered, status unknown.
How it's used in studies
500 mg extended-release once daily in the scarring alopecia series. Mouse topical formulations are experimental.
Side effects and safety
Stomach upset is common, lactic acidosis is rare, and kidney function limits use.
Bottom line
Human data are limited to a 12-patient series for one rare scarring alopecia. Do not start it for hair. Discuss with a doctor.
Fun facts
- A diabetes pill nudged dormant mouse follicles into growth, and in 12 women with scarring alopecia half showed regrowth (uncontrolled). Bao 2024
Studies 3
Chai M et al. Stimulation of hair growth by small molecules that activate autophagy. Cell Rep. 2019
Result: Metformin, rapamycin and alpha-ketoglutarate started growth in resting follicles through autophagy; oral alpha-ketobutyrate prevented hair loss in aged mice.
Read the study ↗Bao A et al. Low-dose metformin and profibrotic signature in central centrifugal cicatricial alopecia. JAMA Dermatol. 2024
Tested: extended-release metformin 500 mg daily added to usual care
Result: 9 improved on symptoms and 6 showed regrowth after at least 6 months; uncontrolled; author industry disclosures.
Read the study ↗Mai Q et al. Robust metformin nanosystem promotes hair growth in androgenetic alopecia. Research. 2025
Result: A metformin-loaded nanosheet beat topical minoxidil with fewer side effects.
Read the study ↗Related
- Rapamycin (sirolimus)The longevity-world favourite is a hair paradox: one 2019 mouse study found it starts hair growth, while older and 2013 mouse work found it does not or even delays it, and mTOR-pathway cancer drugs can cause hair loss.
- Alpha-ketoglutarate (and alpha-ketobutyrate)Two ordinary body metabolites woke dormant mouse hair follicles in a 2019 study, and oral alpha-ketobutyrate prevented hair loss in aged mice, but there is no human data.
- SpironolactoneA cheap blood-pressure pill that blocks androgen receptors and is the most widely used off-label hormonal treatment for women's pattern hair loss.
- GLP-1 receptor agonists (semaglutide, tirzepatide)The new weight-loss injections list hair shedding as a side effect in about 3-6% of trial participants versus about 1% on placebo, far more often in women, and it appears tied to weight loss rather than toxicity to follicles.