(finasteride) belongs to a class of medications called 5-alpha-reductase inhibitors.   Taken in pill form, Propecia is a prescription drug used to treat hair loss due to male pattern baldness by targeting dihydrotestosterone (DHT). DHT, a hormone that some men are more genetically susceptible to, shortens the growth phase of the hair cycle and causes a miniaturization of the follicles (healthy hair being replaced by thinner, finer hair). Proscar, in 5 mg doses, was the first finasteride-based medication manufactured by Merck

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