Proscar is in the family of drugs commonly used to treat or prevent benign enlargement of the prostate gland and to restore hair growth. It inhibits an enzyme that converts the principal male hormone, testosterone, to its more potent form, dihydrotestosterone. Thus, it is a mild form of hormonal therapy. In my opinion, Proscar might mask the presence of prostate cancer for a time, allowing more aggressive cancer cells to develop. In addition, Proscar has adverse effects on sexual function in some men. Recent studies have reported that men taking Proscar had a 25% lower rate of prostate cancer during 7 years of follow-up but a significantly higher rate of high-grade aggressive appearing prostate cancer. Various explanations have been offered to explain this paradox. I believe the most likely explanation is that Proscar might be able to mask low-grade cancer better than high-grade cancer and it also shrinks the prostate gland. So, when men taking Proscar undergo prostate biopsy, it is more likely that high-grade prostate cancer will be found and less likely that low-grade prostate cancer will be found. Some doctors recommend taking Proscar to prevent prostate cancer; however, I do not. In my opinion, more research is needed before the safety of Proscar, Propecia or another similar drug, called Avodart, in the prevention of prostate cancer can be established. I would not recommend taking these for preventing prostate cancer or even as a first-line therapy for benign prostatic enlargement or baldness (Propecia). Other classes of drugs, called alpha-blockers, are helpful in relieving the symptoms of an enlarged prostate in many patients, and they do not carry a risk of masking prostate cancer. Some examples of these are Flomax, Cardura, and Hytrin.