Propecia (finasteride) is a medicine known to prevent the conversion of testosterone to dihydrotestosterone therefore helping men taking it to re-grow some of the hair they lost. Propecia must never be taken by pregnant or breastfeeding women, as it can cause harm to an unborn or nursing baby. Mild side effects are sometimes possible when Propecia is taken. Make sure you let your doctor know if any of the following mild side effects change in intensity or get bothersome: decreased amount of semen, swelling or tenderness in your breasts, decreased sexual desire, runny nose, pain in the testicles, headache, and impotence. If Propecia is taken for hair loss, it will be efficient for only as long as you are using it. Make sure you continue taking it even if you notice no results because up to three months may be required for you not notice the first benefits of the treatment. Tell your health care provider if you have any medical conditions that may prevent you from safely taking this medicine, such as stricture of the urethra, inability to urinate, prostate cancer, abnormal liver enzyme tests, liver disease, and bladder muscle disorder. Your dose may need to be adjusted for you to benefit from taking Propecia.