The active ingredient in horny goat weed, icariin, has been studied for its ability to increase testosterone levels. In this study, male rats were injected with a chemical that damaged the reproductive system and then treated with icariin in one group and testosterone in another group to determine icariin’s effect on testosterone levels.
The researchers concluded:
Icariin improved the condition of reproductive organs and increased the circulating levels of testosterone. Icarrin suppressed the extent of cell death of penile cavernosal smooth muscle cells.