By David Kiefer, MD

Clinical Assistant Professor, Department of Family Medicine, University of Wisconsin; Clinical Assistant Professor of Medicine, Arizona Center for Integrative Medicine, University of Arizona, Tucson

Dr. Kiefer reports no financial relationships relevant to this field of study.


  • If the conflicts of interest in this study are considered insignificant, the product Tribestan at a dose of 500 mg three times daily for 12 weeks can be considered for men with mild-to-moderate erectile dysfunction (who fit the inclusion criteria).

SYNOPSIS: This double-blind, randomized, controlled trial in 180 men showed that a standardized extract of Tribulus terrestris improved erectile function after 12 weeks of treatment.

SOURCE: Kamenov Z, Fileva S, Kalinov K, Jannini EA. Evaluation of the efficacy and safety of Tribulus terrestris in male sexual dysfunction — A prospective, randomized, double-blind, placebo-controlled clinical trial. Maturitas 2017;99:20-26.

Erectile dysfunction (ED) is not negligible in terms of the number of men who suffer from this disorder, not to mention the fact for those who have ED there can be significant, long-term morbidity. Regardless of the cause, ED is not always easily treated, hence the search for treatments in addition to exploring secondary causes and using the pharmaceutical options available. Tribulus terrestris is an herbal medicine with a history of use in traditional Chinese medicine and India. Often it is standardized to a particular concentration of one of the active phytochemical classes, the furostanol saponins. This trial included men 18 to 65 years of age with mild-moderate ED as defined by the International Index of Erectile Function (IIEF). They also could have had low libido, secondary to other causes; primary low libido was considered an exclusion. There was a long list of other exclusion criteria, including a wide variety of comorbidities and pharmaceutical treatments that could affect erectile function and libido.

The patients were randomized to placebo or treatment with the herbal medicine, Tribulus terrestris. The herbal group took two tablets of a Bulgarian-origin Tribulus totaling 500 mg of the herb, three times daily. Each tablet was a 35-45:1 extract of the plant, and the total content of furostanol saponins per tablet was at least 112.5 mg. This extract was a patented product called Tribestan, and was deemed unique from Tribulus products from other geographic regions because of some purported variations in phytochemical content. Unfortunately, two of the authors have ties to the manufacturer of Tribestan, and the manufacturer paid for the study, although independent statisticians were used to analyze the data. The paper clearly stated these potential conflicts.

A total of 180 patients underwent randomization; the 90 patients in each group were similar demographically, and in rates of mild and moderate ED, hypertension, and diabetes. An intention-to-treat analysis of the 86 men to complete each arm of the trial revealed a significant difference between the Tribulus and placebo groups, even after just four weeks of treatment. Specifically, the IIEF in the Tribulus group improved to 22.76 from 18.01, while the placebo group only improved to 20.19 from 18.22; this difference at 12 weeks had a P value < 0.0001. The statistical analysis considered this change an odds ratio of 2.70. A variety of secondary endpoints also were detailed, including the Global Efficacy Question and Overall Estimation of Sexual Function (with four sub-parts), both of which showed benefits to treatment with Tribulus. The therapy was well tolerated, and no significant differences were reported between the Tribulus and placebo groups with respect to adverse effects. Several mechanisms of action were postulated, including effects modulated through the DHEA hormone pathway, or the relaxation of the corpus cavernosum, although an effect on serum testosterone (another possible mechanism) was not seen. The authors were specific in their connection of these mechanisms to the Bulgarian variety of Tribulus and the particular phytochemicals involved; other extracts and varieties may not show the same efficacy.