Tribulus Terrestris

Tribulus terrestris is a low-growing annual found across warm regions worldwide, named for its hard spiked fruit. It appears in both Ayurvedic practice, as gokshura, and in traditional Chinese medicine, generally for urinary and reproductive complaints.

Protodioscin, a steroidal saponin, is the marker compound, and extracts are standardised to saponin content, commonly 40 to 95 per cent. Content varies considerably with the plant part used and its geographic origin, with Bulgarian and Indian material differing meaningfully.

It occupies an unusual place in supplement history as one of the original testosterone boosters, dominant in the 1990s and 2000s. Its persistence in the market owes more to that legacy positioning than to accumulated evidence, and it is a useful case study in how a category can be built on an unexamined premise.

The original proposed mechanism was that protodioscin increases luteinising hormone, which would in turn stimulate testicular testosterone production. This chain has not been demonstrated in humans, and trials measuring luteinising hormone have generally found no change.

A more plausible route for the libido findings involves nitric oxide, which governs blood flow to peripheral tissue. Protodioscin has been reported to increase nitric oxide release in animal models, which would affect sexual function without touching hormone levels at all.

This is an important distinction that marketing routinely blurs. Libido and testosterone are not the same thing, and a compound can affect the first while leaving the second entirely unchanged. Tribulus appears to be exactly that case.

On testosterone the evidence is clear and negative. Multiple controlled trials in healthy men, including in trained athletes across several weeks of supplementation, have found no significant increase in testosterone compared with placebo. Systematic reviews have reached the same conclusion.

On body composition and strength, trials in resistance-trained men have similarly found no benefit over placebo. This is a reasonably settled question rather than an open one.

Sexual function is the more interesting area. Some trials, including in men and women with reduced sexual desire, have reported improvements in libido measures independent of hormonal change. That evidence is limited and populations specific, but it is the part of the tribulus story with any support behind it.

Generally well tolerated, with digestive upset, cramping and occasional restlessness reported. It has a long history of traditional use at customary doses.

There are isolated reports of adverse effects associated with tribulus-containing products, some involving very high intakes or multi-ingredient formulas where attribution is uncertain. The signal is weak but not absent.

Animal studies at high doses have reported effects on reproduction and development, which is the reason for the pregnancy contraindication. Tribulus may also lower blood sugar and blood pressure.