Finasteride is an antiandrogenic compound or ‘testosterone blocker’ which is used as a treatment for an enlarged prostate and can treat male hair loss. It inhibits the production of the enzyme Type-II 5a-reductase which converts testosterone into the more active metabolite 5a-dihydrotestosterone (DHT). DHT is responsible for the development and enlargement of the prostate and can contribute to hair loss by shortening hair follicles and causing them to fall out more quickly. By suppressing production of DHT, finasteride directly targets the molecule responsible for stimulation of prostatic growth. Finasteride is commonly sold under the brand name Proscar and in 2016 was the 75th most prescribed drug in the USA. This application brief describes the use of a Quasar C18 column to analyze finasteride in accordance with the official Finasteride Tablets USP monograph.