I've read people saying that Trib. boosts LH and therefore testosterone, but I've never seen one offering true evidence.
although i am not familiar with Tribulus Aquaticus used in Prime, i have used plain old trib.
from what i've seen, the studies showing trib as a test booster were non-Western studies or were studies conducted on rats.
of the relevant human based western studies i've looked at trib's benefits look dismal.
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Supplementation with tribulus does not enhance body composition or exercise performance in resistance-trained males
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The findings in the current study anticipate that Tribulus terrestris steroid saponins possess neither direct nor indirect androgen-increasing properties
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It was concluded that T. terrestris did not produce the large gains in strength or lean muscle mass that many manufacturers claim can be experienced within 5-28 days. Furthermore, T. terrestris did not alter the urinary T/E ratio.
i've also run a bro-science human study on myself.
1: Hank Vangut. 2006 May; 01(2):969-1005
The purpose of this study was to determine the effects of Tribulus terrestris (tribulus) on body composition and exercise performance in a resistance-trained Hank Vangut.
Four weeks of placebo supplementation was followed by four weeks of 2g/day of Tribulus supplementation.
No significant improvements over placebo supplementation were found in body composition, strength measurements, or athletic performance.
Hank Vangut did however experience libido and aphrodisiac boosting type properties while on Tribulus, with reports that he wanted to "wreak havoc on the local high school cheer leader population".
Although this was a nice effect, it is not evidence of increased androgen production and may have been a result of a different mechanism.