Tribulus Terrestris

What it is

Tribulus terrestris is a herb from the caltrop family (Zygophyllaceae), found in South Africa, Australia, Europe and India, among other places. In German it is also called Erdstachelnuss. The fruits and the herb are used, mostly as an extract. In the traditional medicine of China and India, the plant has long been regarded as a remedy for vitality and sexual function.

The most important constituents are steroidal saponins, above all furostanol saponins such as protodioscin. This is precisely where a practical problem lies. The saponin content varies greatly depending on origin, plant part and extraction method, and one review therefore calls for consistent standardization. Two Tribulus products are therefore not automatically comparable, and strictly speaking, study results apply only to the product tested.

How it is supposed to work

Advertising explains the effect via testosterone: protodioscin is said to stimulate the body’s own testosterone production. In some animal studies, testosterone did indeed rise. In humans this pathway has not been confirmed, and the assumed mechanisms have not yet been demonstrated at the molecular level.

A second explanation focuses on the blood vessels. One review suggests that Tribulus promotes the release of nitric oxide, a messenger that dilates blood vessels. That would explain why erections improve although testosterone stays the same. This mechanism has not been demonstrated in humans either, but it fits the clinical data better than the hormone hypothesis.

Why products differ so much

The positive studies on erections mostly used standardized extracts with a known saponin content, the largest product, for example, with at least 112.5 mg of furostanol saponins per tablet. According to one review, the saponin content varies greatly between products. The studies in men in the 2025 review used 400 to 750 mg per day over 1 to 3 months. Anyone who wants to apply the study results to themselves therefore needs a product that comes as close as possible to the one tested, and patience over several weeks.

What the studies show

The largest placebo-controlled study, 2017

180 men between 18 and 65 years of age with mild to moderate erectile dysfunction received a standardized Tribulus extract or placebo, double-blind, for 12 weeks; 86 per group completed the study. The IIEF score improved significantly more under Tribulus, with a difference of 2.70 points. The product tested was a herbal medicine from Bulgaria in a phase IV study, that is, after approval.

The negative study, 2014

30 men aged 40 and over with erectile problems took Tribulus or placebo for 30 days. The IIEF-5 rose in both groups, but there was no difference between the groups (P = 0.7914). Total testosterone did not change either. The study was small and short, but it shows how large the placebo effect is in this area.

Review on testosterone and erections, 2025

The systematic review evaluated 10 studies with 483 men between 16 and 70 years of age, half of them of low methodological quality. In 8 of 10 studies, androgens did not change; the participants there had normal baseline levels. Only 2 studies in hypogonadism showed an increase of 60 to 70 ng/dl, which is clinically small. Erections improved in 3 of 5 studies.

Meta-analysis on erectile dysfunction, 2026

The analysis included 8 studies. Compared with placebo, the IIEF-5 rose by 3.23 points and the more detailed IIEF-15 by 14.44 points. There was no difference between the groups in total testosterone, nor in side effects. The authors see Tribulus as a possible option with a relatively good safety profile.

Men with late-onset hypogonadism, 2019

70 older men with low testosterone, erectile dysfunction and prostate symptoms received Tribulus or placebo for 3 months, 35 per group. In the Tribulus group, the IIEF-5 rose from 10.7 to 16.1 and total testosterone from 2.2 to 2.7, while prostate symptoms remained the same. However, the liver value AST and the PSA also rose slightly. The results are based on before-and-after comparisons within the group; the direct comparison with placebo is not reported in the abstract.

Where the data stop

The central advertising promise does not stand up to the studies. In men with normal hormone levels, Tribulus does not raise testosterone, as two systematic reviews consistently show. An older review found an increase in humans only when Tribulus was part of a combination product and considers the marketing claims unsupported. For muscle building and performance, too, a review of 7 studies in athletes found no clear effect.

For erections the studies are positive, but small and methodologically inconsistent; half are of low quality. The studies in women have very low certainty according to GRADE. Added to this is the standardization problem: the positive results often come from one particular extract adjusted for saponins and cannot simply be transferred to any capsule. Long-term data beyond 3 months are largely lacking.

Status, approval and legal

In Germany, Tribulus is available as a dietary supplement. According to the European Commission’s Novel Food Catalogue, the fruits and herb are not considered novel in dietary supplements. No medicine containing Tribulus approved in Germany was found; the extract tested in the largest study is a herbal medicine from Bulgaria. There are no authorized health claims, including none on testosterone or potency. Tribulus is not on the WADA Prohibited List 2026.

Safety

In the controlled studies, Tribulus was well tolerated, side effects did not occur more often than with placebo, and sports studies reported no toxicity. In a study with 70 older men, the liver value AST and the PSA rose slightly, which may matter for PSA checks. There are rare case reports of serious side effects: a young man with jaundice and acute kidney failure, and a 43-year-old who temporarily needed dialysis after herbal remedies containing Tribulus. There is no upper limit from EFSA, BfR or NIH. Data for pregnancy and breastfeeding are lacking. Anyone who has kidney disease or takes erectile dysfunction drugs or blood pressure medication should have Tribulus checked by a doctor.

Sources

• Suharyani et al., Int J Impot Res 2026
• Vilar Neto et al., Nutrients 2025
• Kamenov et al., Maturitas 2017
• Santos et al., Actas Urol Esp 2014
• Qureshi et al., J Diet Suppl 2014
• Martimbianco et al., Rev Bras Ginecol Obstet 2020
• Fernández-Lázaro et al., Int J Environ Res Public Health 2022
• Ștefănescu et al., Biomolecules 2020
• GamalEl Din et al., Urologia 2019
• European Commission, Novel Food Catalogue