Clinical studies showed that side effects in men using Propecia were not common and did not affect most men although a small number of men had sexual side effects, occurring in less than 2 percent of men. These included less desire for sex, difficulty in achieving an erection, and a decrease in the amount of semen. The reason men experienced these side effects was not discovered however, they went away in men who stopped taking Propecia.

The following side effects have also been reported while taking Propecia; allergic reactions including rash, itching, hives, and swelling of the lips and face; problems with ejaculation; breast tenderness and enlargement; and testicular pain. Anyone who notes any changes in your breasts such as lumps, pain, or nipple discharge should seek immediate advice from their doctor. Similarly, it is important to consult a doctor before taking this or any other drug because other conditions or medications may affect the way the drug reacts to you.

Women should not use or handle Propecia when pregnant, an ingredient in Propecia, is Finasteride which is not indicated for use by women and women should not to take or handle this medication. In the United States Food and Drug Administration, Finasteride is a pregnancy category X. and this means that it is known to cause birth defects in an unborn baby. The medication could be absorbed through the skin while being handled and Propecia is known to cause birth defects in a developing male baby. Exposure to whole tablets should be avoided whenever possible; however exposure to whole tablets is not expected to be harmful as long as the tablets are not swallowed but women should just avoid handling the pills altogether.  There is no knowledge as to whether Finasteride passes into breast milk an it appears that Finasteride does pass into the semen of men, but caution should be used to avoid ingestion of semen during oral sex if a woman is pregnant or may become pregnant.

Propecia is the first and only FDA-approved pill for the treatment of male pattern hair loss on the vertex and the anterior mid-scalp for use in men only.

It is known that chemical imbalances and family history are the reasons for hair loss but a substance found in your body called DHT that can shrink the hair follicle until it no longer produces visible hair. For men with a family history of hair loss, DHT is believed to contribute to their hair loss. You should consult your doctor if you experience other side effects not included on the list of known effects.