Here's one article, I'll try to look for some more. All the articles and studies I've read show no proof of tribulus claims. I've used it twice, 2 different brands and no positive effects at all. Just my opinion.
Tribulus Terrestris
Description:
Tribulus (puncture vine) is a vine that has been used as a general tonic (energy) and herbal treatment for impotence, but is found primarily in dietary supplements marketed for increasing testosterone levels in bodybuilders and power athletes.
Claims:
Increased testosterone production
Increased muscle mass/strength
Theory:
The idea behind tribulus is that it may increase testosterone levels indirectly by raising blood levels of another hormone, luteinizing hormone (LH). LH is a hormone produced by the pituitary gland and plays a role in regulating natural testosterone production and serum levels.
Scientific Support:
The active ingredient in tribulus is unknown, but is though to be a component known as furostanol saponins. There has been very little research conducted on the effectiveness of tribulus in elevating testosterone levels – the main claim made by body building products which contain the herb. In some cultures, the tribulus terrestris plant has been used as a "tonic" to in crease energy levels and treat sexual dysfunction (usually in males). In animals, tribulus may stimulate "mounting" behavior. Some European studies suggest that tribulus extract can increase testosterone levels 30-50% above baseline levels – but still well within the normal range. Unfortunately, however, these same studies also suggest a similar increase in estradiol levels – not exactly what the hardcore muscle builders should be interested in boosting
If tribulus extract does indeed elevate testosterone levels somewhat, but keeps them within normal ranges, it may be an effective supplement for individuals with reduced testosterone levels such as athletes at risk for overtraining syndrome and in those individuals on a prolonged low-calorie diet. It will not, however, cause you to start sprouting muscles from all parts of your body, as many body building mags would have you believe.
In one of the few well-controlled studies to examine the effects of tribulus terrestris on body composition and exercise performance looked at 15 resistance-trained males. Subjects received either a placebo or a large dose of tribulus (1.5mg per pound of body weight per day for 2 months). Results showed no changes in body weight, percentage fat, total muscle mass or muscle strength related to tribulus supplementation
Safety:
Although no significant side effects should be expected at doses of tribulus contained in commercial dietary supplements, animal studies have suggested the possibility of locomotor (muscle coordination) disturbances following ingestion of tribulus in high quantities. In sheep consuming tribulus plant for several months, neurological disease was characterized by an irreversible, asymmetrical, weakness of the hindlimbs.
Value:
Products containing tribulus are typically marketed to bodybuilders and athletes concerned with increasing muscle mass and strength. Although such products are typically combinations of ingredients which include tribulus, rather than tribulus alone, the scientific evidence for product effectiveness is typically lacking. At this time, Supplement Watch does not view tribulus extract (on its own) as a valuable dietary supplement for muscle building. As a support ingredient contained in a wider supplement blend, tribulus may provide some benefits to those individuals interested in maintaining testosterone levels in the normal range (overtrained athletes and dieters).
Dosage:
A typical dosage of 250-1500 mg of tribulus per day is fairly common. Be sure to choose an extract standardized for at least 30-45% steroidal saponins (furostanol).
References:
1. Antonio J, Uelmen J, Rodriguez R, Earnest C. The effects of Tribulus terrestris on body composition and exercise performance in resistance-trained males. Int J Sport Nutr Exerc Metab. 2000 Jun;10(2):208-15.
2. Arcasoy HB, Erenmemisoglu A, Tekol Y, Kurucu S, Kartal M. Effect of Tribulus terrestris L. saponin mixture on some smooth muscle preparations: a preliminary study. Boll Chim Farm. 1998 Dec;137(11):473-5.
3. Bourke CA. Hepatopathy in sheep associated with Tribulus terrestris. Aust Vet J. 1983 Jun;60(6):189.
4. Bourke CA. Staggers in sheep associated with the ingestion of Tribulus terrestris. Aust Vet J. 1984 Nov;61(11):360-3.
5. Duhan A, Chauhan BM, Punia D. Nutritional value of some non-conventional plant foods of India. Plant Foods Hum Nutr. 1992 Jul;42(3):193-200.
6. Wu G, Jiang S, Jiang F, Zhu D, Wu H, Jiang S. Steroidal glycosides from Tribulus terrestris. Phytochemistry. 1996 Aug;42(6):1677-81.
7. Xu YX, Chen HS, Liang HQ, Gu ZB, Liu WY, Leung WN, Li TJ. Three new saponins from Tribulus terrestris. Planta Med. 2000 Aug;66(6):545-50.
8. Yan W, Ohtani K, Kasai R, Yamasaki K. Steroidal saponins from fruits of Tribulus terrestris. Phytochemistry. 1996 Jul;42(5):1417-22[
