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Tribulus terrestris has no hormonal effects

Tribulus terrestris has no hormonal effects
The claims made by Tribulus terrestris supplements sellers are unfounded. Physiologists at the Universidade Federal do Parana in Brazil come to this conclusion in an animal study that will be published soon in the Journal of Ethnopharmacology. In experiments that they did, tribulus had no hormonal effects on rats.

In countries around the Mediterranean, herbal healers traditionally use extracts of the plant Tribulus terrestris as a remedy for infertility and impotence problems. Modern scientific studies have also confirmed the efficacy of tribulus for these complaints. In addition, however, the supplements industry started selling the same tribulus as a sports supplement, claiming that tribulus raises testosterone levels. One theory that supplements companies use to support their claims is that natural steroid compounds in tribulus are converted into DHEA or another testosterone prohormone.

The Brazilians decided to see whether this theory holds water. They gave the tribulus supplement Androsten, produced by the Brazilian supplements company Herbarium, to rats for a period of 28 days in doses of 11, 42 and 110 mg per kg bodyweight. The lowest dose is equivalent to the usual dose used by humans. Other groups of rats were given a daily 5 mg dose of DHEA per kg bodyweight, about ten times the amount that supplements companies advise humans to take, or 0.25 mg/kg testosterone propionate or 0.1 mg/kg ethinyl estradiol. The researchers administered all the hormones, dissolved in rapeseed oil, orally.

The tribulus extracts had no androgenic effect on castrated rats. The animals' prostates did not grow as a result of being given tribulus. The testosterone propionate supplement, however, did have a growth-enhancing effect on the prostate.

Tribulus terrestris has no hormonal effects

When the researchers examined the faeces of the rats in the tribulus groups and compared them with those of the rats that had been given DHEA, they found that the faeces of the latter group contained more metabolites of male sex hormones. The faeces of the rats in the tribulus groups contained the same amounts of androgens as the faeces of the rats that had not had any supplements. So the theory that compounds in Tribulus terrestris are converted into DHEA or related steroid hormones does not hold water.

In female rats whose ovaries had been removed the tribulus extracts also had no hormonal effects, the Brazilians discovered when they compared cells from the uterus of rats in the different groups.

Tribulus terrestris has no hormonal effects

A high dose of tribulus – but not the highest dose – did raise the testosterone level of the non-castrated rats, but the effect was not significant.

Tribulus terrestris has no hormonal effects

"Tribulus terrestris is not able to stimulate endocrine sensitive tissues such as the prostate, seminal vesicles, uterus and vagina in Wistar rats, indicating lack of androgenic and estrogenic activity in vivo", the researchers conclude. "We also showed an unchanged level of circulating androgens." The fertility of the rats was improved by the tribulus though.

It was already known that the manufacturers’ claims for tribulus supplements are not true. In 2008, doping hunters at the University of Lausanne in Switzerland reported that they had not been able to find any hormonal effects in tribulus users. Three years before, Bulgarian researchers had discovered that healthy men do not produce more testosterone as a result of taking Tribulus terrestris, [J Ethnopharmacol. 2005 Oct 3;101(1-3):319-23.] and five years before that, sports scientists at the University of Nebraska reported that power athletes had nothing to gain from taking tribulus. [Int J Sport Nutr Exerc Metab. 2000 Jun;10(2):208-15.]

A Tribulus variety that may have some effect is Tribulus alatus.

J Ethnopharmacol. 2009 Sep 22. [Epub ahead of print].

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