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5α-Reductase inhibitors like finasteride and dutasteride inhibit 5α-reductase type II and/or other isoforms and are able to decrease circulating DHT levels by 65 to 98% depending on the 5α-reductase inhibitor in question.     As such, similarly to the case of 5α-reductase type II deficiency, they provide useful insights in the elucidation of the biological functions of DHT.  5α-Reductase inhibitors were developed and are used primarily for the treatment of BPH. The drugs are able to significantly reduce the size of the prostate gland and to alleviate symptoms of the condition.   Long-term treatment with 5α-reductase inhibitors is also able to significantly reduce the overall risk of prostate cancer, although a simultaneous small increase in the risk of certain high-grade tumors has been observed.  In addition to prostate diseases, 5α-reductase inhibitors have subsequently been developed and introduced for the treatment of pattern hair loss in men.  They are able to prevent further progression of hair loss in most men with the condition and to produce some recovery of hair in about two-thirds of men.  5α-Reductase inhibitors seem to be less effective for pattern hair loss in women on the other hand, although they do still show some effectiveness.  Aside from pattern hair loss, the drugs are also useful in the treatment of hirsutism and can greatly reduce facial and body hair growth in women with the condition.