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One of the most well-known properties of tribulus is as an aphrodisiac. Tribulus does increase sexual function in animal models, and also reportedly improves libido in humans [6-7]. However, this is not necessarily indicative of a testosterone-increasing effect – there are other possible reasons, such as the hypotensive effect of tribulus. There is limited information regarding the effect tribulus ultimately has on testosterone levels.
Two mechanisms have been proposed for these increases – the first being that protodioscin directly increases LH, and the second being that protodioscin increases levels of DHEA, perhaps by functioning as a precursor [3, 9]. The neural effects of DHEA would also explain the aphrodisiac properties [7]. The ultimate effect of tribulus on testosterone levels in healthy humans, and consequently the effect on body composition and exercise performance, remains to be seen. The present research is not promising – a trial in fifteen resistance trained subjects found that tribulus did not improve body composition or strength over an eight week period [10]. On the other hand, this trial may not have even used a tribulus extract with adequate quantities of the active ingredients.
In human trials using tribulus, it has been reported as safe and side effect free [2-3, 17]. The LD50 of tribulus-derived saponins in mice is 813 mg/kg, which is considerably higher than the commonly used dose (which rarely exceeds more than a gram daily of saponins). In conclusion, tribulus is a relatively safe supplement that has aphrodisiac properties. The effect on testosterone levels and related variables is not well established.
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