Description
Tribulus terrestris has been used for centuries in Europe to treat impotence; however, it has recently been touted as an anabolic agent to be used by bodybuilders.
Usage
Tribulus purportedly enhances plasma testosterone concentrations; this effect should theoretically enhance muscle protein accretion (i.e., an anabolic muscle gain effect).
Prevalence
There are no current data on the prevalence or incidence of use.
Chemical Mechanism
The mechanisms underlying the alleged effects of tribulus have yet to be demonstrated. At this point, there are no peer-reviewed studies that have examined whether this herb can increase plasma testosterone.
Clinical Evidence
A placebo-controlled, double-blind study published in the International Journal of Sport Nutrition and Exercise Metabolism examined the effects of tribulus supplementation in a group of resistance-trained men. The dose ingested was 3.21 mg per kg body weight daily for eight weeks. Each subject participated in a heavy resistance-training program. The investigators found no changes in body weight, percentage fat, total body water, dietary intake, or mood states in either group. Thus, in this limited sample of resistance-trained men, the consumption of tribulus daily for eight weeks had no ergogenic effect.
Scientific Research
There is animal data that is of interest. Work by Dimitrov et al. found that a tribulus-containing preparation increased plasma testosterone levels in rams. This occurred supposedly via an increase in luteinizing hormone. However, for the most part, the claims made by supplement companies are not supported by peer-reviewed studies of any sort.
Administration
Tribulus is ingested orally in capsule form.
Dosage
Due to the lack of data showing an ergogenic effect, it is not clear what the proper dosage should be. It also is not clear if there are sex differences.
Contraindications
There is animal data that suggest potential adverse effects. For instance, Australian tribulus has been shown to induce staggers (irreversible, asymmetrical weakness of hindlimbs) and limb paresis in sheep; however, there is no evidence this can occur in humans.
Precautions/Warnings
Clearly, more safety and efficacy data are needed to establish the ergogenic (or ergolytic) effects of tribulus. There are no known harmful interactions with other supplements or drugs.
Banned/Permitted
Neither the International Olympic Committee nor the U.S. Olympic Committee currently includes tribulus on their lists of banned substances.
Legality
Tribulus is a legal substance.
References
Antonio J. et al. The effects of Tribulus terrestris on body composition and exercise performance in resistance-trained males. Int. J. Sport Nutr. Exerc. Metab.10:208-215, 2000.
Bourke, C.A. et al. Locomotor effects in sheep of alkaloids identified in Australian tribulus terrestris.Aust. Vet. J. 69:163-165, 1992.
Dimitrov, M. et al. Use of tribestan in rams with sexual disorders. Vet. Med. Nauki. 25:102-110, 1987.
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