Finasteride is a pill, approved by the FDA for the use for male pattern hair loss in 1997. Taken once a day in a 1 mg dose, it acts by decreasing the body’s level of (DHT) dihydrotesterone, a metabolite of testosterone that can cause hair loss. Studies have shown that it increases hair diameter, growth rate, and to a lesser degree hair count. Stabilization of hair loss has been reported in studies in 51% of men and hair regrowth in 48% of men. It is generally a very well tolerated medication with adverse side effects being rare and reported in 1-2% of patients. This practice has been prescribing it for many years, with many happy patients.
In 2015, some data was brought to the scientific community’s attention about some undesirable side effects. In large clinical trials, some of the reported side effects include decreased libido, erectile dysfunction, and decreased sperm count. Other side effects reported include breast tenderness, breast enlargement, breast nodules, allergic reactions, testicular pain, depression / suicidal ideation, and rare cases of male breast cancer. Upon the discontinuation of the medication, the resolution of the reported sexual dysfunction side effects has resolved, except in a small subset of patients who have reported permanent sexual dysfunction, which is of obvious concern. Note that permanent sexual dysfunction has not been substantiated in double-blind placebo-controlled clinical trials as all symptoms resolved in weeks to months following the discontinuation of the medication.
Finasteride also affects the levels of PSA (prostate-specific antigen), so the male patient should inform his primary physician and/or urologist of his use of the medication.
Finasteride is only approved for the use in men. If a woman is to become pregnant while taking finasteride, it could cause defects in the male fetus.