Some aphrodisiacs do work. Take long jack or tongkat ali for eg. There's a scientific explaination for it and it's rather detailed and comprehensive but the most simplistic explaination would be aphrodisiacs like tong kat ali allow for more free testosterone to be used by the body. Some of the testosterone in the body is bound by some chemical compound and cannot be used by the body. What these aphrodisiacs do is that they free up the testosterone that is bound by the chemical so that the body can make use of it. Take note that aphrodisiacs don't actually cause the body to create more of the male hormone it only frees up more of the hormone that is bounded down. Steroids are the chemicals that allow the body to create more testosterone. Once the body utilizes more testosterone one of the effects is of course a higher sex drive and a higher desire for sex. Viagra does not really create a higher desire for sex. It just allows the male to get an erection even if he isn't horny or lacks the ability to get an erection thru natural means.