Effects of Tribulus (Tribulus terrestris L.) Supplementation on Erectile Dysfunction and Testosterone Levels in Men-A Systematic Review of Clinical Trials.

The short version

This systematic review of 10 clinical studies (483 men in total) examined whether Tribulus terrestris supplements improve erectile dysfunction (ED, difficulty achieving or keeping an erection) and testosterone levels. Tribulus is a plant used for centuries in India and China as a sexual stimulant. Its steroidal saponins (plant compounds with hormone-like structure) are proposed to raise testosterone and to boost nitric oxide, a molecule that relaxes blood vessels and supports erections, though the authors note the mechanism is not fully understood. The review asked whether the evidence supports either claim, and it looked at men with and without low testosterone. Researchers searched 13 databases for studies in which men took Tribulus on its own, without other supplements or drugs. Ten studies qualified: nine clinical trials and one study without a control group, conducted in Egypt, Bulgaria, Brazil, Australia, India, China and Spain. Participants were aged 16 to 70: healthy men, men with ED (some also with low testosterone), and men with low sperm counts or unexplained infertility. Doses ran from 400 mg to 12 g per day for 4 weeks to 3 months. Study quality was graded with the Jadad scale, a 5-point checklist of randomization, blinding and dropouts. Three of the five studies that measured erectile function found improvement, and all three enrolled men with ED. One trial using 500 mg daily for 3 months raised International Index of Erectile Function (IIEF-5) scores against placebo, with significance already at 4 weeks (p = 0.0119) and stronger by the end (p < 0.0001). Eight of ten studies found no significant testosterone change, and those men did not have low testosterone at the start. Two studies in men with low testosterone found rises of about 58 to 71 ng/dL (27 to 33%), a small increase in clinical terms (roughly from 215 to 273 and 213 to 284 ng/dL), and both scored poorly for methodological quality (Jadad 2 and 0). None of the studies reported side effects, and lipid and liver tests showed no impairment. The authors conclude that evidence for improved erectile function at 400 to 750 mg per day is of low level and that no solid evidence shows Tribulus raises testosterone. Half of the studies had a high risk of bias, samples were small, saponin content varied between products, and no meta-analysis was possible. The authors state that Tribulus is not a substitute for first-line treatment of severe ED and call for well-controlled randomized trials to define dose and duration, including trials in men with low testosterone.

Key findings

• A review of 10 clinical studies (483 men) found that Tribulus terrestris, a plant supplement, improved erectile function in 3 of the 5 studies that measured it, at doses of 400 to 750 mg per day for 1 to 3 months.
• Eight of the ten studies found no significant change in testosterone, and the men in those studies did not have low testosterone to begin with.
• Two studies in men with low testosterone (hypogonadism, a shortage of male sex hormone) found rises of about 60 to 70 ng/dL, a small change in clinical terms, and both were methodologically weak (quality scores of 2 and 0 out of 5).
• No included study reported side effects, and lipid and liver blood tests showed no impairment, although the studies were short (4 weeks to 3 months).
• The authors rate the evidence as low because half of the studies had a high risk of bias, and they call for better-controlled randomized trials to establish dose and duration.

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