i'm pretty sure it's because the drug is present in the semen.
A warning about PROSCAR and pregnancy.
PROSCAR is for use by MEN only.
Women who are or may potentially be pregnant must not use PROSCAR. They should also not handle crushed or broken tablets of PROSCAR.
If a woman who is pregnant with a male baby absorbs the active ingredient in PROSCAR after oral use or through the skin, it may cause the male baby to be born with abnormalities of the sex organs.
PROSCAR tablets are coated and will prevent contact with the active ingredient during normal handling, provided that the tablets are not broken or crushed.
If a woman who is pregnant comes into contact with the active ingredient in PROSCAR, a doctor should be consulted.
Remember, these warnings apply only when the woman is pregnant or could potentially be pregnant.
About side effects. Like all prescription drugs, PROSCAR may cause side effects. Side effects due to PROSCAR may include impotence (an inability to have an erection) or less desire for sex.
Some men taking PROSCAR may have changes or problems with ejaculation, such as a decrease in the amount of semen released during sex. This decrease in the amount of semen does not appear to interfere with normal sexual function. In some cases these side effects went away while the patient continued to take PROSCAR.
In addition, some men may have breast swelling and/or tenderness. Some men have reported allergic reactions such as rash, itching, hives, and swelling of the lips and face. Rarely, testicular pain has been reported.