While urban legends claim that drinking Mountain Dew can harm sperm count, no reputable studies have backed up that claim, according to ABC News. Some people have taken this unsupported claim to mean that Mountain Dew can be used as a contraceptive, About.com states.
People who believe that Mountain Dew affects fertility point to the high level of caffeine or the presence of Yellow Dye No. 5 in the drink. However, neither ingredient causes sterility; in fact, About.com states that FDA studies show that caffeine may actually increase sperm cell efficacy. PepsiCo, the maker of Mountain Dew, has stated forthrightly that the claim that Mountain Dew affects fertility is ridiculous.