Finasteride is a type II 5-α reductase inhibitor used to treat symptomatic benign prostatic hypertrophy and male pattern baldness. Inhibition of 5-α reductase decreases the peripheral conversion of testosterone to 5-α dihydrotestosterone. Finasteride causes increased prostatic and serum levels of testosterone and decreases prostatic volume. It may also slow and reverse hair loss in men with male pattern baldness, through poorly understood mechanisms.
The most common side effects are related to sexual dysfunction: decreased libido, erectile dysfunction and infertility. Clinical trials demonstrated an increased risk of high grade prostate cancer and breast cancer, although it remains to be determined whether the relationship between finasteride use and development of malignancies is causational or the result of study design. Finasteride is contraindicated in female patients, children, pregnant patients, and people who have previously experienced hypersensitivity to this drug class.
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