What does finasteride inhibit?

Finasteride specifically inhibits the enzyme 5α-reductase, which plays a crucial role in the conversion of testosterone to dihydrotestosterone (DHT). This inhibition is significant because DHT is a more potent androgen than testosterone and is involved in the development of conditions such as benign prostatic hyperplasia (BPH) and androgenetic alopecia (male pattern baldness). By blocking the action of 5α-reductase, finasteride effectively reduces levels of DHT, leading to a decrease in prostate size in men with BPH and a slowing of hair loss in those experiencing male pattern baldness.

Other options listed are associated with different metabolic pathways; for instance, COX enzymes are involved in the inflammatory process and are the target of nonsteroidal anti-inflammatory drugs (NSAIDs). Xanthine oxidase is important in purine metabolism, and its inhibitors are used to treat gout. Carbonic anhydrase is involved in regulating acid-base balance and is targeted by some diuretics. None of these are relevant to the mechanism of action attributed to finasteride.