Arginine. The amino acid L-arginine, which occurs naturally in food, boosts the body's production of nitric oxide, a compound that facilitates erections by dilating blood vessels in the penis. Studies examining L-arginine's effectiveness against impotence have yielded mixed results. A 1999 trial published in the online journal BJU International found that high doses of L-arginine can help improve sexual function, but only in men with abnormal nitric oxide metabolism, such as that associated with cardiovascular disease. In another study, published in 2003 in the Journal of Sex & Marital Therapy, Bulgarian scientists reported that ED sufferers who took L-arginine along with the pine extract pycnogenol saw major improvements in sexual function with no side effects. Arginine can be helpful, says Geo Espinosa, ND, director of the Integrative Urological Center at NYU Langone Medical Center. Espinosa says that men with known cardiovascular problems should take it only with a doctor's supervision; L-arginine can interact with some medications.