Tribulus terrestris is also known as Puncture Vine and Caltrop fruit. Proponents of its use claim the substance acts as a luteinizing hormone stimulant that can increase the body’s production of testosterone, which in turn would augment protein synthesis.
Claims are based on obscure case studies published in foreign journals that are not easily obtained. Still, despite this lack of evidence, internet and magazine ads appear regularly touting its unfounded effects.
To further fuel the fire, former Eastern block “experts,” now residing in the United States, have begun to speak of “proprietary knowledge and expertise” regarding the use of this formerly guarded “state secret.” Currently, however, there is only one peer-reviewed study available on the use of Tribulus terrestris in healthy resistance-trained subjects.
Of general interest to athletes and those sports medicine professionals dealing with these individuals is that studies used to substantiate advertising claims often deal with disease or deficiency states and are not applicable to healthy populations. This is certainly the case with the data cited by supplement manufacturers marketing Tribulus terrestris.
In one of a handful of studies, Wang et al treated patients with coronary heart disease (CHD) using Tribulus terrestris. According to 406 cases of clinical observation and a cross test (67 cases treated with Yufen Ningxin Pian as control) in this Chinese journal, the results showed that the total rate of remission of angina pectoris was 82.3% in patients treated with Tribulus terrestris versus 67.2% in the control group. Similarly, the total effective rate of ECG improvement (52.7%) was higher than that of the control group (35.8%).
In another study examining the purported hormonal implications, Adimoelja et al. used Tribulus terrestris in the treatment of male subfertility. With the primary aim of examining alternative therapies to hormonal treatment, these investigators examined the use of this traditional herbal medicine used for centuries all over the world. The use of Tribulus terrestris in Asian countries has been claimed to improve strength. To scientifically evaluate these claims, extraction of the active components in this study were performed, identified, and purified. The main active constituent identified was protodioscin, a nonhormonal agent having a steroidal chemical structure similar to dehydroepiandrosterone (DHEA). The dried powder extract was then experimentally administered in a double-blind study involving 45 subfertile men with moderate idiopathic oligozoosperms.
During the trial, 36 of the men were treated with Tribulus terrestris dry powder extract and men were administered a placebo. After 3 months, 7 men were able to conceive with their wives. This was attributed to the enhancement of sperm function after Tribulus terrestris consumption. Further studies involving diabetic impotent men treated with Tribulus terrestris dry powder extract showed a significant increase of DHEA-S blood levels as well as improvement of libido.
Despite these results, two observations should be noted. First, this is not a peer-reviewed study. Second, despite the apparent effect of Tribulus terrestris in a hormonally compromised population, its effectiveness remains to be determined in a healthy male population. To this end, Antonio et al. examined the use of Tribulus terrestris with the express purpose of studying the effects on body composition and exercise performance in resistance-trained males. During this trial, 15 subjects were randomly assigned to a placebo or Tribulus terrestris (3.21 mg/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.
After 8 weeks, there were no changes in body weight, percent body 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 whereas the Tribulus terrestris group experienced an increase in leg press strength only. Therefore, owing to these preliminary data, supplementation with tribulus terrestris does not appear to enhance body composition or exercise performance in resistancetrained males.
Safety and Toxicity
There may be concerns about the safety of long-term, high-dose Tribulus terrestris supplementation in humans. Tribulus terrestris ingestion may cause toxic reactions in animals. It should be noted that “natural” and “herbal” supplements are not safe for all individuals and can be harmful to the health and well-being of athletes if improper dosing or a potentially dangerous substance is used. Tribulus terrestris is promoted as a safe alternative to anabolic steroids despite the fact that no toxicity studies in athletes have been conducted.