Where it comes from: Tribulus terrestris is a flowering plant native to the warm temperate and tropical regions of Europe, southern Asia, Africa and Australia. "It's used in herbal nutritional supplements that are promoted to produce large gains in strength and lean muscle mass," says registered dietitian and American Dietetic Association spokesperson Jim White. "It has also been touted to increase testosterone in men."
What it can do for you: There has been very little research conducted to examine each of these claims—and the studies that have been done, don't weigh exceedingly in the herb's favor:
- Elevates testosterone levels and enhances libido
"The main claim made by body building products containing the herb is that it can elevate testosterone levels," says White. Why would you want to do that? The hormone is essential for maintaining muscle tone, stamina and strength. "But the best way to enhance testosterone is to exercise," White explains. Blood levels of testosterone increase with just 20 minutes of exercise and remain elevated for up to three hours after.
In 2005, Bulgarian researchers organized 21 healthy men (ages 20 to 36) and split them into an experimental and a control group. The first group was given 20 mg per kg of body weight of tribulus terrestris extract and the second group was given just 10 mg per kg. After four weeks, there was no significant difference between the two groups, the levels were considered normal and tribulus terrestris was declared to have no testosterone-increasing properties.
"Some studies in women, however, resulted in a normalization of ovulation, improved fertility and a reduction in peri- and postmenopausal symptoms," White adds. "Most importantly, tribulus terrestris was found to provide better results in women in regards to increasing libido than traditional hormone therapy."
- Increases strength and lean muscle mass
Tribulus terrestris is often marketed with the claim that it will produce large gains in strength and lean muscle mass in just five to 28 days. Australian researchers investigated that claim and studied 22 male elite rugby league players—some were given tribulus terrestris and others were given placebos. After five weeks of training, strength and fat free mass increased significantly in both groups—with no differences between them. The experts concluded the herb does not produce large gains in strength or lean muscle mass.
Suggested intake: A dosage of 85 to 250 mg three times daily with meals is fairly common and considered safe.
Associated risks/scrutiny: Although no significant side effects were found with typical commercial tribulus supplements, animal studies have suggested the possibility of muscle coordination disturbances following ingestion of tribulus in high quantities. "An increase in breast size in a young male weight trainer was reported after he took a herbal tablet containing tribulus," White warns. People with hormone-dependent conditions, such as breast or prostate cancer, should not use the herb.
Some manufacturers claim tribulus terrestris will not lead to a positive drug test, but some experts agree that T. terrestris may increase the urinary testosterone/epitestosterone (T/E) ratio, which may place athletes at risk of a positive drug test.