Tribulus components don't convert to testosterone
Supplements based on the Tribulus terrestris plant do not contain testosterone precursors. Nor do they raise the body's testosterone production. Doping hunters at the University of Lausanne in Switzerland were convinced of this after doing tests with Tribestan, a Tribulus product.
The doping hunters undertook the study in response to drugs tests in which two female athletes were caught. They used an expensive test that measures the ratio between carbon-12 and carbon-13 atoms. When the analysts did urine tests on the athletes, they saw none of the usual signs of drugs use.
The athletes that were caught attributed the positive results of the doping test to the Tribulus supplements they were using. These contain the furostanol protodioscin, which is related to cholesterol.
This substance, claim supplements manufacturers, is converted into testosterone in the body. But according to organic chemists, the human body does not contain any of the enzymes needed to do this conversion. So far research has proved the organic chemists right. In human tests, Tribulus does not raise the testosterone level. [J Ethnopharmacol. 2005 Oct 3;101(1-3):319-23.] If you give weight trainers Tribulus their performance does not improve. [Int J Sport Nutr Exerc Metab. 2000 Jun;10(2):208-15.] A recent study on the performance-enhancing effects of Tribulus found no evidence to support this either. [J Strength Cond Res. 2007 May;21(2):348-53.]
But the doping analysts in Lausanne were not interested in performance enhancement. The only thing they wanted to know was whether Tribulus can show up positive in a drugs test. So they gave two female athletes Tribestan for two consecutive days. Tribestan is the Tribulus supplement manufactured by Sopharma, the first company to launch Tribulus on the market. The athletes were given a five hundred mg dose three times a day.
The researchers found no effect on the DHEA-level. The graph below shows the DHEA concentration in one of the test subject's urine.
The relationship between testosterone and epitestosterone didn't change either. That would indicate that the components in Tribulus do not make the body produce more testosterone or DHEA. So the theory put out by supplements manufacturers, that Tribulus imitates the effect of messenger hormones like LH, doesn't look like it holds water.
The idea was that protodioscin converts into testosterone metabolites, such as androsterone, androstenol or etiocholanolone.
The figure above shows the structure of androsterone, a DHT metabolite. Etiocholanolone – structure shown here – is the 5-alpha-analogue of androsterone. Etiocholanolone is the DHEA and testosterone metabolite that gives some users fever and can affect the immune system.
Androstenol is the steroid shown below. Androstenol is a pheromone, and is a metabolite of androstenone.
The researchers looked at the composition of the three metabolites in the urine. More specifically, they determined which carbon atoms were present in the molecules of the three metabolites, measuring the ratio between C-12 and C-13. Molecules from plant material have a different C-12/C-13 ratio from that of molecules that are produced by the human body. If it were components from the Tribulus that were converted into the metabolites, you should be able to see that in the isotope ratio. The graph below shows the isotope ratios for the three metabolites in the urine of one of the athletes. There is no effect to be seen.
Athletes that test positive are going to have to think up a new excuse.
Forensic Sci Int. 2008 Jun 10;178(1):e7-10.