Finasteride is a 5alpha-reductase inhibitor approved for the treatment of male pattern hair loss. Originally approved for the treatment of benign prostatic hypertrophy in 1992, its approval was expanded in 1997 to include the treatment of androgenetic alopecia (AGA) in men at a dose of 1 mg/day. Finasteride inhibits 5alpha-reductase, thereby prohibiting the conversion of testosterone to dihydrotestosterone (DHT), which is implicated in the development of hairless in some men. Reduction in DHT results in a significant improvement in subjective and objective assessments of hair growth and density. Finasteride is well-tolerated with a favourable adverse event history. The most common adverse events include reduced libido, decreased ejaculate volume and gynaecomastia.