Metformin is primarily known for managing blood sugar levels, but it is also used as a treatment option for women experiencing excessive hair growth, known as hirsutism. Hirsutism is characterized by the growth of coarse, dark hair in a male-like pattern, typically on the face, chest, and back. This article explores the biological connection between Metformin and hair growth reduction, the science behind its action, and the clinical evidence regarding its effectiveness.
Understanding Hirsutism and Its Hormonal Roots
Hirsutism is a dermatological manifestation of hormonal imbalance. It occurs when hair follicles are stimulated by an excess of androgens, hormones present in all women but normally at lower concentrations. Elevated levels of androgens, such as testosterone, cause fine vellus hairs to transform into thick, pigmented terminal hairs.
The most common underlying cause is Polycystic Ovary Syndrome (PCOS). A key feature of PCOS is insulin resistance, where the body’s tissues become less responsive to insulin, leading to high circulating insulin, known as hyperinsulinemia. This excess insulin directly stimulates the ovaries and adrenal glands to produce more androgens.
Insulin also reduces the liver’s production of Sex Hormone-Binding Globulin (SHBG), a protein that binds to and deactivates androgens. The resulting combination of increased production and reduced deactivation leads to higher levels of “free” androgens. These free androgens then act on hair follicles and cause hirsutism, which provides the rationale for using Metformin to treat the symptom.
Metformin’s Action on Androgen Levels
Metformin is an insulin-sensitizing agent that makes the body’s cells more responsive to insulin. It works by reducing the liver’s glucose production and improving glucose uptake in tissues, leading to a reduction in circulating insulin.
Lowered insulin levels reduce the hyperstimulation of the ovaries and adrenal glands. Since excessive insulin drives these organs to produce androgens, reducing the insulin signal lowers the production of testosterone and related hormones. Metformin may also directly impact androgen production within the adrenal and ovarian cells by regulating enzymes involved in steroid hormone synthesis.
The decrease in hyperinsulinemia also helps normalize the liver’s production of SHBG. Increased SHBG levels bind to more free androgens in the circulation. This dual mechanism—reducing androgen production and increasing their clearance—addresses the root hormonal cause of hirsutism, creating an environment less conducive to terminal hair growth.
Clinical Evidence of Hair Reduction
Clinical studies have investigated Metformin’s ability to reduce hirsutism, primarily in women diagnosed with PCOS. Effectiveness is measured using the Ferriman-Gallwey (F-G) score, a standardized method for quantifying hair growth across nine body areas. Research indicates that Metformin can lead to a clinically relevant improvement in hirsutism scores compared to a placebo.
The efficacy of Metformin as a standalone treatment is moderate. While some trials show it is comparable to traditional anti-androgen treatments, its effect on circulating androgen levels can be modest. The drug’s benefit is most pronounced when the underlying cause is strongly linked to hyperinsulinemia.
A limitation in observing results is the natural hair growth cycle. Existing hair must complete its life cycle before the hormonal changes induced by Metformin become physically visible. Due to this slow turnover, improvements in hair reduction typically take many months of consistent treatment to become apparent.
What to Expect During Treatment
Metformin treatment for hirsutism typically begins with a low dose, such as 500 milligrams (mg) once or twice daily. The dose is gradually increased over several weeks to minimize adverse effects, often reaching an effective range between 1,000 mg and 1,700 mg per day.
The most common side effects are gastrointestinal. Patients frequently report nausea, diarrhea, stomach upset, and bloating, which can affect up to one-third of individuals starting the medication. Taking the medication with meals or using the extended-release formulation can help alleviate these digestive issues.
Visible changes in hair growth are not immediate due to the lengthy hair follicle cycle. Patients should expect to wait six to twelve months before noticeable softening or reduction in hair growth is observed. Metformin must be taken under the supervision of a healthcare provider who can monitor kidney function and other health parameters during treatment.