Tribulus terrestris has gotten increasing attention over the past decade, as a supplement to help body builders, and as an aphrodisiac. This herb is known as gokshura in Ayurveda, where it is considered a libido booster with the ability to calm an agitated mind. Initially, it was thought that Tribulus was a plant source of testosterone. Recent research has shown that this is not exactly the case. A 2005 study showed that the herb does not increase testosterone production in young men. A 2007 study showed that Tribulus does not change either testosterone levels, or the ratio of testosterone to epitestosterone (one measure that can cause an athlete to fail a drug test). (PMID 15994038, PMID 17530942) But Tribulus does affect the testosterone receptors.

Tribulus does contain steroidal saponins that stimulate the testosterone receptors directly, without changing testosterone levels. A study at the National University of Singapore showed that tribulus extract increased the activity of androgen receptors in rats' brains by 58%, and this was accompanied by an increase in penis blood pressure and sexual activity. (PMID 15588660)

At least 8 different steroidal saponins have been found in tribulus. (PMID 10985082, PMID 15501264, PMID 16631216). While these are not identical to steroids found in the body, they are chemically close enough to have some of the same effects.

Tribulus lowers blood pressure (PMID 16289603) and opens blood vessels. This action appears to be largely (but not entirely) due to an increase in nitric oxide production. Viagra and other male potency drugs work directly to increase nitric oxide, while testosterone and other hormones also increase nitric in a less direct manner.

In Ayurveda, gokshura is considered relaxing or nervine. Tribulus is a prominent ingredient in the Dashamularishta formula. The Chinese Baisong Tablet formula (which contains tribulus) has been shown to block hormonal changes caused by chronic stress; this might also contribute to an aphrodisiac effect.
(PMID 15719645)

Tribulus grows in dry areas across the Southwestern United States - it is sometimes called puncture vine because the seeds have sharp thorns that can puncture bicycle tires.

Precautions and Toxicity

A 2004 study reported a case of enlarged breasts (gynaecomastia or 'bitch-tits') in a male weight lifter taking a compound that was labeled as tribulus. The product itself was not tested to determine if it contained any banned steroids, or if it was actually tribulus. (PMID 15454201)

A friend who was a competitive weight-lifter tells me that "Bulgarian Tribulus" has been used as a code word for various steroid preparations. The Bulgarian Olympic team made some very public announcements about how tribulus was helping their athletes - around the same time that they suddenly improved. While many of the products marketed as Bulgarian tribulus do not contain steroids, it is likely that some have in the past.

While man-boobs might be hypothetically be a side-effect of gokshura, the evidence isn't convincing. Taking a non-steroid spiked brand of tribulus, and taking it at the recommended dose has yet to cause little nips to turn into big jugs. A potentially greater danger is related to neurological side-effects seen in animals that consume too much tribulus.

Sheep that graze on areas containing large amounts of Tribulus can develop a motor neuron disease that is similar to Parkinsons disease. The symptoms include a disturbed ability to walk, with characteristic staggers. As with parkinson's disease, there is damage to the dopamine neurons in the nigrostriatal region of the brain.

Tribulus motor neuron disease typically occurs in sheep that eat lots of the herb - when they are pastured on areas where tribulus makes up a 20, 30, or 40% of their diet.

It is not certain what in Tribulus causes the development of motor neuron disease - one study suggests that it is an alkaloid called tribulusterene, which is present in the plant in very small doses. (Actahort study).

The prudent person should be asking the following questions about tribulus:

• Do humans respond to the toxic compound in tribulus the same way sheep do?
• Do small amounts of the toxin have a cummulative, permanent effect, or can the body safely handle small doses?
• Do the extracts on the market today contain significant amounts of the toxin, or is it removed in processing?

Until these questions are satisfactorily answered, I am taking a cautious approach to this herb. I have taken it occassionally and have noticed a nice boost, but will not take a large dose at any one time, or a small dose for long periods.

Other Effects of Tribulus

• A few studies have found that tribulus saponins can lower total cholesterol, LDL ("bad") cholesterol, and trigylcerides.
• Tribulus inhibits ACE (angiotensin converting enzyme), which suggests a use for the herb in controlling blood pressure.
• Like many herbs, it has anti-fungal and anti-bacterial properties and it is more toxic to many cancer cells than to normal cells.