Tribulus terrestris L., a member of the Zygophyllaceae family, is an annual herb found in many areas of the world, including the US and Mexico, the Mediterranian region, and throughout Asia [1-4]. It is also used in the folk medicine of many areas, such as India, China, and Turkey [1, 3]. Traditional uses include treatment of sexual impotency, edema, abdominal distention, cardiovascular disease, kidney problems, and as a cough remedy [1, 3]. It also has a reputation for having anabolic effects in some areas of the world [4]. A large amount of potential active components have been identified in tribulus, including steroidal saponins, lignanamides, alkaloids, and flavanoids [5]. The amount of these components can vary significantly based on the region of origin and the part of the plant used [1-2]. HPLC analysis of different tribulus supplements revealed significant product-to-product variations in active ingredients [4], presumably due to different regions of origin. The current research indicates that the steroidal saponins, particularly the dominant saponin protodioscin, are responsible for the pharmacological activities of tribulus [4].
One of the most well-known properties of tribulus is as an aphrodisiac, and as a putative testosterone elevator. Tribulus does increase sexual function in animal models, and also reportedly improves libido in humans [6-7]. However, this is not necessarily indicative of a testosterone-increasing effect – there are other possible reasons, such as the hypotensive effect of tribulus. There is limited information regarding the effect tribulus ultimately has on testosterone levels. Translated Bulgarian research indicates that tribulus increased testosterone and luteinizing hormone (LH) levels in depressed men who were part of infertile couples [8]. When protodioscin is administered to castrated rats, it increases levels of testosterone, LH, DHEA, and DHT [7].
Two mechanisms have been proposed for these increases – the first being that protodioscin directly increases LH, and the second being that protodioscin increases levels of DHEA (which would ultimately mildly increase testosterone), perhaps by functioning as a precursor [3, 9]. The neural effects of DHEA would also explain the aphrodisiac properties [7]. However, it should be noted that if the latter is the case, it would open the possibility that tribulus could ultimately lead to lower natural production of testosterone. The ultimate effect of tribulus on testosterone levels in healthy humans, and consequently the effect on body composition and exercise performance, remains to be seen. The present research is not promising – a trial in fifteen resistance trained subjects found that tribulus did not improve body composition or strength over an eight week period [10]. On the other hand, this trial may not have even used a tribulus extract with adequate quantities of the active ingredients.
There has also been clinical research on the use of tribulus in many medical conditions, usually with positive results. Biological properties of tribulus extracts include diuretic properties, increased endothelial nitric oxide, direct smooth muscle relaxant effects, and ACE inhibition [2, 11]. In vitro, tribulus also inhibits COX-2 [12]. Cardiovascular conditions in which tribulus has showed promise include high blood pressure, high cholesterol, coronary heart disease, and angina pectoris [2-3, 13]. In both normal and diabetic mice, tribulus decreases serum glucose, perhaps by inhibiting gluconeogenesis [14-15]. Tribulus also inhibits stone formation in experimental animals [3] and may have hepatoprotective properties [16]. It may also be useful in the treatment of vitiligo and bacterial infections [3]. A number of other uses have been reported in traditional medical systems.
In human trials using tribulus, it has been reported as safe and side effect free [2-3, 17]. One trial reported no negative effect on the circulatory system or hepatic and renal function [17]. Toxic effects have been observed in sheep fed large amounts of tribulus [18], but are not likely to be applicable to normal supplemental use by humans. The LD50 of tribulus-derived saponins in mice is 813 mg/kg, which is considerably higher than the commonly used dose (which rarely exceeds more than a gram daily of saponins). In conclusion, tribulus is a relatively safe supplement that has aphrodisiac properties and may be beneficial to the cardiovascular system. The effect on testosterone levels and related variables is not well established.
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References:
1. Fitoterapia. 2003 Sep;74(6):583-91. Furostanol saponins from Tribulus terrestris. De Combarieu E, Fuzzati N, Lovati M, Mercalli E.
2. Life Sci. 2003 Oct 24;73(23):2963-71. Study of antihypertensive mechanism of Tribulus terrestris in 2K1C hypertensive rats: role of tissue ACE activity. Sharifi AM, Darabi R, Akbarloo N.
3. J Ethnopharmacol. 2003 Apr;85(2-3):257-60. Tribulus terrestris: preliminary study of its diuretic and contractile effects and comparison with Zea mays. Al-Ali M, Wahbi S, Twaij H, Al-Badr A.
4. J Pharm Sci. 2001 Nov;90(11):1752-8. Determination of steroidal saponins in Tribulus terrestris by reversed-phase high-performance liquid chromatography and evaporative light scattering detection. Ganzera M, Bedir E, Khan IA.
5. J Nat Prod. 2000 Dec;63(12):1699-701. New steroidal glycosides from the fruits of Tribulus terrestris. Bedir E, Khan IA.
6. Ann Acad Med Singapore. 2000 Jan;29(1):22-6. Proerectile pharmacological effects of Tribulus terrestris extract on the rabbit corpus cavernosum. Adaikan PG, Gauthaman K, Prasad RN, Ng SC.
7. Life Sci. 2002 Aug 9;71(12):1385-96. Aphrodisiac properties of Tribulus Terrestris extract (Protodioscin) in normal and castrated rats. Gauthaman K, Adaikan PG, Prasad RN.
8. Am J Clin Nutr. 2000 Aug;72(2 Suppl):624S-36S. Selected herbals and human exercise performance. Bucci LR.
9. J Am Coll Nutr. 2001 Oct;20(5):520-8. Endocrine and lipid responses to chronic androstenediol-herbal supplementation in 30 to 58 year old men. Brown GA, Vukovich MD, Martini ER, Kohut ML, Franke WD, Jackson DA, King DS.
10. Int J Sport Nutr Exerc Metab. 2000 Jun;10(2):208-15. The effects of Tribulus terrestris on body composition and exercise performance in resistance-trained males. Antonio J, Uelmen J, Rodriguez R, Earnest C.
11. Boll Chim Farm. 1998 Dec;137(11):473-5. Effect of Tribulus terrestris L. saponin mixture on some smooth muscle preparations: a preliminary study. Arcasoy HB, Erenmemisoglu A, Tekol Y, Kurucu S, Kartal M.
12. J Ethnopharmacol. 2002 Nov;83(1-2):153-9. Evaluation of natural products on inhibition of inducible cyclooxygenase (COX-2) and nitric oxide synthase (iNOS) in cultured mouse macrophage cells. Hong CH, Hur SK, Oh OJ, Kim SS, Nam KA, Lee SK.
13. Zhong Yao Cai. 2003 May;26(5):341-4. [Effect of saponin from Tribulus terrestris on hyperlipidemia] [Article in Chinese] Chu S, Qu W, Pang X, Sun B, Huang X.
14. Zhong Yao Cai. 2002 Jun;25(6):420-2. [Hypoglycemic effect of saponin from Tribulus terrestris] [Article in Chinese] Li M, Qu W, Wang Y, Wan H, Tian C.
15. Zhong Yao Cai. 2001 Aug;24(8):586-8. [Effect of the decoction of tribulus terrestris on mice gluconeogenesis] [Article in Chinese] Li M, Qu W, Chu S, Wang H, Tian C, Tu M.
16. Planta Med. 1998 Oct;64(7):628-31. Tribulusamide A and B, new hepatoprotective lignanamides from the fruits of Tribulus terrestris: indications of cytoprotective activity in murine hepatocyte culture. Li JX, Shi Q, Xiong QB, Prasain JK, Tezuka Y, Hareyama T, Wang ZT, Tanaka K, Namba T, Kadota S.
17. Zhong Xi Yi Jie He Za Zhi. 1990 Feb;10(2):85-7, 68. [406 cases of angina pectoris in coronary heart disease treated with saponin of Tribulus terrestris] [Article in Chinese] Wang B, Ma L, Liu T.
18. Vet Res Commun. 2003 Jan;27(1):53-62. Experimental Tribulus terrestris poisoning in sheep: clinical, laboratory and pathological findings. Aslani MR, Movassaghi AR, Mohri M, Pedram M, Abavisani A.
