It works by inhibiting the enzyme 5-alpha reductase, which converts testosterone into dihydrotestosterone (DHT), a hormone that can contribute to hair loss and prostate growth
Free testosterone in circulation is actually increased, usually by about 10-20%
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It will increase testosterone levels in the body, which decreases prostate size
Finasteride inhibits the 5-alpha-reductase enzyme from converting testosterone to dihydrotesterone (DHT), the androgen we usually associate with body hair and head hair after puberty (it has a major role in the development of the body and puberty, more so than testosterone, but I don't think it affects these things (much) later in life)
Finasteride vs Dutasteride: What’s the right First approved in 1992 in the treatment of benign prostatic hypertrophy, finasteride was approved for the treatment of alopecia in 1997 at a dose of 1 mg daily (propecia ®)
Hair follicle miniaturization is caused hypoxia of the follicle by mechanisms of DHT due to the presence of 5a reductase type 2 in the Though rare, in clinical trials, 3
Testosterone in this case simply acts as a prohormone that is converted to the active androgen DHT by the action of the enzyme 5alpha reductase (5-AR)
Aldactone (spironolactone) is most commonly used, but other drugs like Propecia (finasteride), Avodart (dutasteride), and Eulexin (flutamide) may also be prescribed
Typically, the cost of Propecia is around $75-$80 a month