Extract standardized to saponins, depending on the product.
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Tribulus terrestris, popularly known as caltrop or puncturevine, or gokshura in Ayurveda, is a creeping plant with spiny fruits common in warm and arid regions around the world; its traditional use includes urological and reproductive indications and as a general tonic in Ayurvedic (where it is considered a rasayana, or rejuvenating tonic), Chinese, and European medicine (especially Bulgarian and Roman, where it became popular in the 1970s as a natural ergogenic aid for athletes); its entry into the modern sports supplement market is based on the promise, frequently promoted but clinically less well supported, of significantly increasing endogenous testosterone concentrations, a claim that deserves careful analysis in light of the available evidence.
The active components identified are steroidal saponins (especially protodioscin), flavonoids, and alkaloids; commercial products are typically standardized to the percentage of total saponins or specifically to protodioscin; there is significant variability in composition depending on the geographic origin of the plant (Bulgarian plants are traditionally the most studied and have a profile different from Indian or Chinese ones) and on processing, which contributes to the heterogeneity of the clinical results observed.
The central commercial promise of tribulus as a supplement is an increase in testosterone, a claim with a limited basis in rigorous clinical evidence: most trials in healthy adult men with normal baseline testosterone have not shown significant increases in total or free testosterone with supplementation at commercial doses (250-1,500 mg/day) for weeks to months; the Australian study by Brown and colleagues published in 2000, with 22 trained men over 4 weeks, showed no effects on testosterone or strength, a result replicated in later studies with similar cohorts.
Some studies in men with mild erectile dysfunction or low baseline testosterone levels have shown modest improvements in subjective scales of sexual function and male well-being, possibly independent of significant changes in testosterone; these modest effects could explain part of the anecdotal satisfaction reported by users, but reasonable expectations of tribulus as a "testosterone booster" should be very modest.
In libido and male and female sexual function, the data are more positive: several small trials have documented subjective improvements in sexual desire with supplementation at 250-750 mg/day of standardized extract for 30-90 days, an indication consistent with traditional use although with modest magnitudes that depend on baseline status.
In male infertility with mild oligospermia, several small studies have documented modest improvements in sperm parameters with supplementation for 3-6 months, an indication consistent with traditional use although robust clinical evidence is limited.
In strength performance and body composition, the data are consistently disappointing: most rigorous trials have not shown significant improvements with tribulus compared with placebo, a conclusion that holds in systematic reviews and that calls into question the use of tribulus specifically for strength-related ergogenic purposes.
The doses studied range from 250 to 1,500 milligrams daily of extract standardized to saponins (ideally 40-60 percent), divided into one or two doses with or without food; the effect on libido and subjective well-being appears gradually and requires at least 4-8 weeks for clinical evaluation.
Generally well tolerated at usual supplemental doses; the adverse effects described are rare and mild (mild digestive discomfort, occasionally headache or irritability at high doses); people with hormone-dependent cancers (especially prostate) should exercise theoretical caution because of activity on the hormonal axis, although the effects on testosterone are questionable; those taking hormone replacement therapy or antiandrogen treatments should consult beforehand; those taking hypoglycemic drugs, antihypertensives, or anticoagulants should monitor for possible mild potentiation; people with kidney stones may experience exacerbation because some components of tribulus may contribute to stone formation in predisposed people; it is contraindicated in pregnancy; in breastfeeding the data are limited and it is not recommended; it is not recommended for those under 18 because of activity on hormonal development; non-standardized products vary enormously in clinical efficacy; the reasonable clinical position is: as a supplement to raise testosterone, the data are disappointing and commercial expectations are frequently exaggerated; for libido and male well-being with a normal hormonal profile, it may offer modest benefits as an adjunct; for strength performance, the data are insufficient to recommend it as an ergogenic aid.
Information, not medical advice. Scientific evidence reflects the quality of the studies.