Propecia Mechanism of Action

Pharmacology: PROPECIA (finasteride, MSD) is a synthetic 4-azasteroid compound that is a specific inhibitor of Type II 5α‑reductase, an intracellular enzyme that metabolizes the androgen testosterone into dihydrotestosterone (DHT).
Pharmacodynamics: Results of Clinical Studies: The effect of PROPECIA on male pattern hair loss has been demonstrated in 3 studies in more than 1,800 men. Two of these studies were done over a 5-year period in men with different amounts of hair loss and with balding at the top of the head. The third study was conducted for 1 year in men with balding at the front of the head.
A special photographic method was used to count the number of hairs in a balding area of the scalp. In general, men who took PROPECIA maintained or showed an increase in the number of hairs and noticed improvement in their hair, with benefit continuing with long term use. At the same time, those who did not take PROPECIA continued to lose their hair.
At each clinic visit, men in the studies were also asked to fill out a questionnaire and rate the change in appearance of their hair and their satisfaction with the treatment result. For every question asked, men treated with PROPECIA reported greater improvement than those who did not receive PROPECIA. Men who took PROPECIA reported improvements as early as 3 months after beginning treatment. Improvements continued throughout the 5 years of treatment.
These men were also rated by physicians who determined whether there was an increase or decrease in scalp hair. The ratings were based on a balding scale and on photographs of the patient's head taken before, during, and at the end of the studies. Almost all men treated with PROPECIA for 5 years had no further hair loss and many of these men had improved hair growth as rated by physicians.