Taken from: Adverse effects of cannabis, by Hall W, Solowij N (1998):
"Chronic administration of THC to animals lowers testerone secretion, impairs sperm production, mobility, and viability and disrupts the ovulary cycle. Whether these effects affect humans is uncertain because the published evidence is small and incosistent."
Note:
1) THC was administrated. There are 200+ other chemicals in weed that could effect your little doods.
Personally its an aphrodiasiac to me.