What Do We Know About 5-Alpha Reductase Inhibitors?

Five years ago, a study at the Instituto de Dermatologia Integral in Madrid, Spain, reviewed the efficacy and safety of 5-alpha reductase inhibitors, finasteride and dutasteride, in treating benign prostatic hyperplasia and androgenic alopecia. Finasteride, approved by the FDA in 1991 and 1997, reduces dihydrotestosterone (DHT) levels by 70% at a 5mg/day dose. Dutasteride, approved by the FDA in 2002, reduces DHT levels by over 90% at a 0.5mg/day dose. Both drugs were classified as Level I evidence in treating male androgenetic alopecia, but were associated with a low incidence of reversible sexual side effects. In women, finasteride was classified as Level III evidence, and a 2017 review found that 1mg/day finasteride did not yield better outcomes than a placebo. The study also explored alternative uses of these drugs, such as topical finasteride and capillary mesotherapy with dutasteride.