Arginine (l-arginine) is the amino acid that supplies the body with the neurotransmitter nitric oxide (NO). As neurotransmitter, nitric oxide plays a specific role in facilitating erections. In combination with lysine, arginine is also used by body builders in an attempt to trick the body into releasing growth hormone.

Pure arginine is one of the more popular amino acid supplements. By and large, there are two groups of users: body builders and people who want to enhance their sexual functions.

Bodybuilders usually combine arginine with either ornithine or lysine to release growth hormone. The idea behind taking arginine to enhance sexual function is based on the fact that the body metabolizes nitric oxide from arginine, and nitric oxide works as neurotransmitter responsible or at least partially responsible for penile and clitoral erections. There are a number of scientific studies supporting the theory that nitric oxide, metabolized from arginine, indeed is necessary to make erections possible at all. However, it is less clear whether taking arginine as supplements beyond a usual intake in food will improve sexual function. And even more doubts exist as to whether arginine supplements can correct erectile dysfunction effected by causes other than arginine deficiency.

Arginine may enhance sexual function not only via the nitric oxide route but via the growth hormone route as well. The release of growth hormone has long been associated with an increase of sexual desire. A sensible idea is to test oneself whether taking arginine supplements will do one good or not. If dosages of a few gram per day do not have the desired effect, one may as well give up on arginine. To just increase arginine dosages is an approach unlikely to have the desired effect, and may even be harmful as arginine is proven to facilitate the replication of viruses.

Therefore, excess arginine consumption, in food or as supplements, has been associated with herpes outbreaks in infected people.

Lysine is an amino acid that balances arginine. An example of a amino acid-balanced diet is oats and milk. While oats are rich in arginine, milk is a prime food source for lysine. As mentioned above, the combination of arginine and lysine is believed to further the release of growth hormone.