I've read from Wikipedia (perhaps not-reliable but it's still a great place to go for information) and pubmed, and this is what they say.
cliffs:The extract is claimed to increase the body's natural testosterone levels and thereby improve male sexual performance and help build muscle. Its purported muscle-building potential was popularized by American IFBB bodybuilding champion Jeffrey Petermann in the early 1970s. However, T. terrestris has consistently failed to increase testosterone levels in controlled studies. It has also failed to demonstrate strength-enhancing properties - a finding indicating that the anabolic steroid effects of Tribulus terrestris may be more myth than fact.
>extract of tribulus claims to increase bodys test levels
>consistently failed to increase test levels in controlled studies
>failed to demonstrate strength-enhancing properties
cliffs:The purpose of this study was to determine the effects of the herbal preparation Tribulus terrestris (tribulus) on body composition and exercise performance in resistance-trained males. Fifteen subjects were randomly assigned to a placebo or tribulus (3.21 mg per kg body weight daily) group. Body weight, body composition, maximal strength, dietary intake, and mood states were determined before and after an 8-week exercise (periodized resistance training) and supplementation period. There were no changes in body weight, percentage fat, total body water, dietary intake, or mood states in either group. Muscle endurance (determined by the maximal number of repetitions at 100-200% of body weight) increased for the bench and leg press exercises in the placebo group (p <.05; bench press +/-28.4%, leg press +/-28.6%), while the tribulus group experienced an increase in leg press strength only (bench press +/-3.1%, not significant; leg press +/-28.6%, p <.05). Supplementation with tribulus does not enhance body composition or exercise performance in resistance-trained males.
>15 resistance-trained males assigned to placebo or tribulus
>No changes in body composition in either group
>Placebo group had increase in bench and leg press
>Tribulus group only eperienced increase in leg press
I've heard constantly that tribulus is the thing to get when it comes to naturally increasing your testerone, but these two things say otherwise. I'd like someone to prove me wrong please