Tribulus terrestris is a testosterone enhancer. Studies show that it works very well when stacked with DHEA and androstenedione. It increased testosterone levels in a different way, however, than either DHEA or andro do. Instead of being a testosterone precursor, it leads to the production of the luteinizing hormone (LH). When LH levels are increased, the natural production of testosterone also increases. LH is a hormone that also deals with sex drive. Now one can understand why it has been used in the sex products.