Propecia (finasteride) can be prescribed by your health care provider if you experience thinning of hair on your scalp - a condition known as male pattern hair loss. Another reason why you may be prescribed this medicine is to treat benign prostatic hyperplasia. This drug is intended for oral administration and should be taken at the same time every day for quite a long period of time. Propecia will be efficient for as long as you continue taking it. As soon as you stop the treatment you will lose all the hair you have managed to re-grow within a one year period. In case you have been taking this medicine for 12 months and still see no improvement this medicine is unlikely to work for you. In that case talk to your health care provider to find out what your options are. Impotence is one of the side effects of Propecia. While in some cases drug interactions are so dangerous you have to choose just one medicine to go with, in case of Propecia you can take some anti-impotence drugs (such as Viagra) and it will cause no interaction. In most cases Propecia is well tolerated and the few mild side effects that you may get tend to go away very soon on their own. However, some patients due to their individual sensitivity to some of the ingredients this medicine contains may develop serious side effects that require prompt medical attention and qualified advice. It's important that you let your health care provider know about any of the following serious side effects in case of having them: hives, swelling of the lips and face, breast pain, itching, rash, lumps in the breast, or nipple discharge.