An amino acid hyped as a testosterone booster, this supplement has little evidence to back its claims and has been associated with side effects that include increased prolactin levels and breast enlargement, bloating, anxiety, headaches and confusion. It appears makers of testosterone therapies put a new twist on this marketing scheme. Manufacturers like Eli Lilly & Co. and Abbott Laboratories are riding on the successful marketing of Viagra and other erectile dysfunction treatments to encourage relatively healthy men to try testosterone therapy.