We need to be very clear that Propecia, also sold under the name Finasteride, is used to treat two very different problems. The first is to slow the development of benign growths in the prostate. The second is the slowing of hair loss. You will understand that the first use was well established before the side effect was noticed. When Merck & Co realized the same drug might prevent hair loss in healthy men, it began full-scale clinical trials and gained FDA approval for this use. As a result, this drug has become one of the steady earning drugs for the manufacturer as men rely on the treatment to retain a full head of hair. However, in this history lies the same reality. This drug is actually designed to affect the prostate and, by implication, the surrounding areas including all the sexual apparatus. There always has been some level of interference with both the general level of interest in sex and the functional side of generating and maintaining an erection, ejaculation, sperm count, and so on.
The original studies suggested these were purely temporary disruptions and that, as soon as you stopped taking the drug, the sexual problems would quickly disappear. This has proved an optimistic expectation for the minoirity of men affected. The FDA has reviewed more than 400 post-marketing reports of sexual dysfunction and has concluded that men can expect the sexual problems to last at least three months after discontinuing use of Propecia. There may also be periods of depression or increased anxiety. Some experts are saying that, in a small number of cases, men who have taken the drug over many years may be permanently disabled. It's still to early to say with any degree of confidence. In the most recent of studies, it appears that about 2% of men experience some sexual difficulties. This is a relatively small percentage but nevertheless a level of risk you should take seriously. The moral of the story appears to be that, if you prove to be one of the small percentage, stop taking the drug sooner rather than later. The longer you expose your body knowing that damage may be sustained, the more likely it is to be damaged permanently.