Tribulus

Tribulus terrestris L. belongs to Zygophyllaceae, the caltrop family, and was published by Linnaeus in Species Plantarum in 1753 (Kew’s Plants of the World Online, POWO). Kew describes it as an annual or biennial native to the Old World, from Portugal, Spain, and North Africa across sub-Saharan Africa, southern and eastern Europe, the Middle East, Central Asia, India, China, Korea, Japan, and Southeast Asia, and lists it as introduced in North and South America, Australia, New Zealand, and many Pacific islands. Sources disagree about Australia: Kew treats Australian populations as introduced, while Washington State’s Noxious Weed Control Board lists Australia among its native regions. The Flora of North America calls it native to the Mediterranean region and now found throughout drier temperate areas of the world, recorded as introduced in more than 40 US states as well as British Columbia and Ontario. Common names describe the burr: puncture vine, goathead, caltrop, tackweed, devil’s thorn, and cat’s-head in English, gokshura in Sanskrit, gokhru in Hindi, and bai ji li in Chinese. Chhatre and colleagues (Pharmacognosy Reviews 2014) explain that go-ksura means cow’s hoof, after the shape of the fruit, and Ștefănescu and colleagues (Biomolecules 2020) trace the genus name to the Greek tribolos, a spiky fruit.

It is a prostrate, mat-forming herb. The Flora of North America describes hairy stems up to 1 m long, green to reddish, and leaves 2–4.5 cm long divided into 6 to 12, occasionally 16, small oval leaflets that are silvery and silky when young. The Washington weed board describes stems radiating from a simple, woody taproot and forming dense mats, with individual stems up to about 6 feet long. The flowers are small, about 5 mm across and occasionally up to 10 mm, with five yellow petals, and sit singly on short stalks at the leaf nodes; UC IPM, the University of California’s pest management program, notes that plants can flower within three weeks of germinating and keep flowering through the summer. The fruit is the plant’s signature: a woody, roughly five-angled burr about 1–1.5 cm across that splits at maturity into five wedge-shaped segments, each armed with a pair of stout spines 3–7 mm long and sometimes a smaller pair near the base. Some say each segment resembles a goat’s head. The segments lodge in tires, shoes, and animal feet, which is how the plant travels. A single plant usually produces 200 to 5,000 seeds, which can stay viable in the soil for up to five years (UC IPM).

Those spines make it a serious weed. The Flora of North America records that Arizona, California, Colorado, Hawaii, Idaho, Iowa, Michigan, Nebraska, Nevada, North Carolina, Oregon, Washington, and Wyoming have declared it a noxious weed; Washington has listed it as a Class B noxious weed since 1988 and also bans its sale. After about 50 years of unsuccessful chemical control, California imported two weevils from India in 1961 to eat its seeds and stems, with cyclical success. Chemically, tribulus is best known for steroidal saponins, plant compounds built on a steroid skeleton, notably protodioscin (PubChem CID 441891, C51H84O22), along with flavonoids such as rutin and beta-carboline alkaloids such as harmane. Composition varies widely. Dinchev and colleagues (Phytochemistry 2008) compared plants from Bulgaria, Greece, Serbia, Macedonia, Turkey, Georgia, Iran, Vietnam, and India. The southeast European and west Asian samples shared a profile dominated by protodioscin and prototribestin, while the Indian and Vietnamese samples lacked prototribestin and tribestin, contained large amounts of tribulosin, and appeared to belong to different chemotypes. Content also varied by plant part and stage of growth.

Tribulus has been used for centuries in the traditional medicine of India and China. Chhatre and colleagues (Pharmacognosy Reviews 2014) describe gokshura in Ayurveda as nourishing, aphrodisiac, a remover of urinary stones, and a remedy for bladder ailments, used for impotence, sexual debility, and genitourinary disorders, and as a key ingredient of Gokshuradi guggulu, a formula used to support the urinary tract and clear stones. They note that the Ayurvedic Pharmacopoeia of India also attributes heart-tonic properties to the root and fruit. In traditional Chinese medicine, the same authors record use of the fruit for eye trouble, edema, abdominal distension, involuntary emission of semen, abnormal vaginal discharge, and sexual dysfunction, and describe it as a valued drug in the Shennong pharmacopoeia, which they call the oldest known pharmacological work in China. In Unani medicine it served as a diuretic, mild laxative, and general tonic. MSKCC adds chest pain, heart problems, dizziness, skin disorders, and the expulsion of kidney stones to its traditional uses. The dried fruit has official monographs in the pharmacopoeias of China, Japan, and Korea and in the Siddha Pharmacopoeia of India (Ștefănescu and colleagues 2020).

The modern supplement story begins in Bulgaria. Pokrywka and colleagues (Journal of Human Kinetics 2014) write that the first scientific reports of benefit came from Bulgarian pharmaceutical researchers, who claimed that tribulus extracts increased libido, blood testosterone, and sperm production, and that a preparation named Tribestan was used in Bulgaria from the 1970s. The product’s reputation in sport grew alongside Bulgarian weightlifting, and it was suggested that Bulgarian athletes owed part of their performance to it. Pokrywka and colleagues add a pointed caveat: that was a time when Bulgarian weightlifters were world champions until more accurate anti-doping tests revealed their use of anabolic-androgenic steroids, so tribulus cannot be credited with their medals. Tribestan, made by the Bulgarian company Sopharma at the time of a 2017 trial, contains 250 mg per tablet of a concentrated extract of the plant’s aerial parts standardized to at least 112.5 mg of furostanol saponins (Kamenov and colleagues 2017). Qureshi and colleagues (2014) note that tribulus is now widely used by athletes and bodybuilders on the strength of marketing claims that it raises testosterone, and the Flora of North America observes that extracts of this troublesome weed are sold online to treat male infertility and build muscle.

In much of the West the plant was known first as a nuisance. Its common name, caltrop, is shared with an old military device, four metal spikes arranged so that whichever way it lands one spike points upward, used to stop hooves and tires (UC IPM); the burrs behave in much the same way, puncturing bicycle tires and shoe soles and injuring livestock, people, and pets. Ranchers also learned that it poisons sheep, and veterinary reports from South Africa, Australia, Argentina, and California describe outbreaks of liver damage and sun sensitivity in grazing flocks. As a supplement in the United States, tribulus has not been reviewed by the Food and Drug Administration (FDA) for safety or effectiveness and cannot be marketed to treat or cure a disease, as WebMD notes. It is not on the Department of Defense list of prohibited supplement ingredients, and OPSS says it should not cause a positive result on a routine military drug test. The Australian Institute of Sport, however, advises athletes against tribulus because it and other claimed testosterone boosters are banned or carry a high risk of contamination with substances that can cause a positive doping test (ODS).

Tribulus is marketed on the idea that its saponins, especially protodioscin, raise testosterone, either directly or by increasing luteinizing hormone (LH), the pituitary signal that tells the testes to make testosterone. Some animal work points that way: MSKCC cites a study in primates, rabbits, and rats in which protodioscin was linked to increases in some sex hormones, and a rat study in which tribulus increased sperm production. Human studies do not bear it out. Neychev and Mitev (Journal of Ethnopharmacology 2005) gave 21 healthy men aged 20 to 36 placebo or 10 or 20 mg/kg of extract a day for four weeks and found no difference in testosterone, androstenedione, or LH. Qureshi and colleagues (Journal of Dietary Supplements 2014) reviewed 11 studies and found that testosterone rose in humans only when tribulus was combined with other ingredients. In a 2025 review in Nutrients, Vilar Neto and colleagues found no change in androgens in 8 of 10 studies; the two exceptions involved men with low testosterone and showed rises of only about 60–70 ng/dL. In 2016 Neychev and Mitev concluded that the long-held view of tribulus as an androgen enhancer was outdated.

If tribulus helps sexual function, other mechanisms look more plausible. Laboratory and animal studies suggest that tribulus extracts relax the spongy erectile tissue of the penis, the corpus cavernosum, through the blood vessel lining and nitric oxide, the same signaling pathway that drugs such as sildenafil amplify (MSKCC; Neychev and Mitev 2016). Qureshi and colleagues suggested that this nitric oxide effect could explain responses to tribulus independent of testosterone. Another proposal is that protodioscin is converted in the body to dehydroepiandrosterone (DHEA), a weak precursor of sex hormones. Findings in women point in different directions. In an uncontrolled review of hospital records for 120 women given tribulus for sexual dysfunction, Gama and colleagues (Clinical Medicine Insights: Women’s Health 2014) found that DHEA rose while total and free testosterone fell. By contrast, two small Brazilian placebo-controlled trials reported rises in free and bioavailable testosterone in postmenopausal and premenopausal women (de Souza and colleagues 2016; Vale and colleagues 2018). These studies are small and inconsistent, and none of the proposed mechanisms has been confirmed in well-designed human research.

Tribulus has other laboratory effects that matter mostly for safety. MSKCC summarizes animal studies in which extracts lowered blood pressure by relaxing arterial muscle, releasing nitric oxide, and inhibiting angiotensin-converting enzyme (ACE), the target of common blood pressure drugs; lowered blood sugar and glycated hemoglobin in diabetic rats; and increased urine output. In the test tube, its saponins inhibited platelet clumping, and saponins and phenolic compounds inhibited P-glycoprotein, a transporter that pumps many medicines out of cells. The plant also contains beta-carboline alkaloids, including harmane and norharmane, which researchers led by Bourke have proposed as possible neurotoxins behind a movement disorder in sheep; Ștefănescu and colleagues note that these alkaloids inhibit monoamine oxidase and suggest caution with MAO-inhibitor antidepressants if the effect holds in people, which has not been tested. In sheep, the steroidal saponins themselves appear to drive liver injury: Kellerman and colleagues (Onderstepoort Journal of Veterinary Research 1991) induced geeldikkop, a liver disease with sun sensitivity, by dosing sheep with crude saponins from tribulus. MSKCC notes that the steroidal compound diosgenin is thought to be responsible for the liver toxicity associated with tribulus.

Raising testosterone and building muscle are tribulus’s biggest markets, and the evidence for both is consistently negative. ODS reviews the trials in its fact sheet on supplements for exercise and athletic performance. Besides the 2005 study in young men, 15 resistance-trained men taking 3.21 mg/kg a day for eight weeks gained no more bench press, leg press, or muscle mass than those on placebo, and in Rogerson and colleagues’ 2007 trial, 22 elite Australian rugby league players taking 450 mg a day during five weeks of preseason training gained strength and lean mass equally with or without tribulus. ODS concludes that the published literature provides no support for its efficacy in enhancing exercise performance. A 2022 systematic review of seven studies in physically active men (Fernández-Lázaro and colleagues) found no clear evidence of benefit on muscle damage markers or hormones, and OPSS notes that small studies in rugby players and CrossFit athletes showed no significant improvement in body composition, strength, or exercise performance. Vilar Neto and colleagues (2025) concluded that there is no robust evidence that tribulus raises testosterone, and WebMD advises anyone worried about their testosterone to ask a clinician about testing and treatment.

Erectile dysfunction has the largest trial in men. Kamenov and colleagues (Maturitas 2017) randomized 180 men aged 18 to 65 with mild or moderate ED, including some with high blood pressure, diabetes, or metabolic syndrome, to Tribestan, two 250 mg tablets three times a day, or placebo for 12 weeks; 86 in each group finished. Scores on the International Index of Erectile Function (IIEF) improved more with tribulus, by 2.7 points over placebo on average, and intercourse satisfaction, orgasm, desire, and overall satisfaction scores also favored it, with no difference in side effects. Not every trial agrees. Santos and colleagues (Actas Urológicas Españolas 2014) gave 30 men aged 40 and over 800 mg a day or placebo for 30 days and found no difference in erectile function or testosterone. Borrelli and colleagues (Drugs 2018) counted two tribulus ED trials with 202 men and called the results mixed; Vilar Neto and colleagues found improvement in 3 of 5 studies that measured erectile function but rated the evidence low; and a 2026 meta-analysis of herbal supplements for ED by Ho and colleagues judged the evidence for tribulus insufficient. MSKCC calls the ED data mixed and not definitive.

Low sexual desire in women is where tribulus looks most promising, though the trials are small. Akhtari and colleagues (DARU 2014) randomized 67 premenopausal women with hypoactive sexual desire disorder (HSDD), persistently low desire that causes distress, to tribulus extract or placebo for four weeks. Among the 60 who finished, the tribulus group improved more in total Female Sexual Function Index (FSFI) score and in the desire, arousal, lubrication, satisfaction, and pain domains, with similar rates of side effects. In Brazil, de Souza and colleagues (Menopause 2016) gave 45 postmenopausal women with low libido 750 mg a day or placebo for 120 days, and 36 finished. FSFI scores improved in both groups, with lubrication improving only on tribulus, while a second questionnaire showed gains in desire, arousal, pain, and orgasm only in the tribulus group. The same research group reported similar results in 40 premenopausal women (Vale and colleagues, Gynecological Endocrinology 2018). Separately, Postigo and colleagues (2016) found better desire, arousal, and comfort during intercourse, but no difference in orgasm or satisfaction, among 60 postmenopausal women after 90 days.

Reviews temper the enthusiasm. Martimbianco and colleagues (Revista Brasileira de Ginecologia e Obstetrícia 2020) found five randomized trials with 279 women: sexual function scores rose after one to three months on tribulus, but the trials were too different to combine, no serious adverse events were reported, and the certainty of the evidence was very low, meaning future studies are likely to change the picture. Sha’ari and colleagues (Phytomedicine 2021) did pool trials and found a sizable improvement over placebo in overall female sexual function, desire, arousal, and orgasm, describing the evidence as preliminary. Several of the positive trials come from a single Brazilian group, products and doses differ, and none lasted more than four months. OPSS agrees that some trials suggest benefit for women with low libido or HSDD but that larger studies are needed, and MSKCC describes the female data as small studies that need large-scale confirmation. None of the trials tested tribulus against an approved treatment, and none addressed hot flashes or other menopause symptoms, so the postmenopausal studies concern desire specifically.

Outside sexual health, single trials hint at metabolic effects. Samani and colleagues (Journal of Evidence-Based Complementary and Alternative Medicine 2016) gave 98 women with type 2 diabetes 1,000 mg of tribulus extract a day or placebo for three months; blood sugar and total and LDL cholesterol fell more with tribulus, which the authors called a preliminary result. In a trial at India’s National Institute of Unani Medicine, Siddiqui and colleagues (Journal of Complementary and Integrative Medicine 2021) gave people with prehypertension, blood pressure above normal but below the threshold for hypertension, 6 g of powdered dried fruit a day or placebo for two months; blood pressure fell by an average of 7.7/5.5 mmHg on tribulus versus 1.9/0.2 mmHg on placebo. Neither finding has been confirmed by independent trials, and neither makes tribulus a substitute for diabetes or blood pressure treatment. Its traditional use for kidney stones rests on laboratory work showing that extracts limit the formation of calcium oxalate and calcium phosphate crystals and on diuretic effects in animals; MSKCC notes that these effects have not been studied in humans.

Tribulus is sold as capsules and tablets of dried extract, as powders, and as one ingredient among many in testosterone, “male vitality,” and pre-workout formulas. Products may be made from the fruit, the root, or the aerial parts (leaves, stems, and fruit), and WebMD notes that each part contains different chemicals, so it is worth checking which part a label names. Many products state a percentage of saponins, but because the saponin mix varies with geography and plant part (Dinchev and colleagues 2008), a headline percentage does not say which saponins are present. The best-studied product, Tribestan, is an extract of the aerial parts concentrated 35 to 45 times and standardized to at least 112.5 mg of furostanol saponins in each 250 mg tablet; the 2017 ED trial used two tablets three times a day, or 1,500 mg daily. Other trials in men used about 400 to 800 mg a day for one to three months (Vilar Neto and colleagues 2025; Santos and colleagues 2014), the postmenopausal desire trial used 750 mg a day, and the diabetes trial 1,000 mg a day. OPSS notes reports of sleep problems and a faster heart rate above 1,000 mg a day.

Traditional preparations center on the dried fruit. Chhatre and colleagues give Ayurvedic doses of 3–6 g of powdered fruit, or 20–30 g of fruit or root boiled into a decoction, and gokshura appears in compound formulas such as Gokshuradi guggulu, Gokshuradi kwatha, and Dashamoola kwatha. The Unani prehypertension trial used 6 g of powdered dried fruit a day, taken in three divided doses. These traditional preparations have not been compared with modern extracts in trials, and a Bulgarian aerial-parts extract, an Indian fruit powder, and a root decoction should be treated as different products. Some traditional uses have no place in self-care: RxList, republishing the Natural Medicines database, records that the plant has been used to cause abortion, which is one reason it should be avoided in pregnancy. Whole burrs are a physical hazard rather than a remedy, and RxList advises against eating the spiny fruit.

Practical points: if you choose to try tribulus, pick a single-ingredient product that names the plant part and the amount of extract, ideally with a third-party certification seal, as OPSS recommends. Be wary of “testosterone booster” and “male enhancement” blends. Pokrywka and colleagues describe tribulus products found to contain anabolic steroids and prohormones that were not listed on the label, and WebMD warns that products marketed for sexual or physical performance have been found to contain prescription medicines or harmful chemicals. Competitive athletes should know that pure tribulus did not change urinary testosterone markers in the rugby trial or in a short Swiss doping-control study (Saudan and colleagues 2008), but a contaminated product can still cause a positive test, and the Australian Institute of Sport advises against it. If you want to see whether it helps, give it a defined trial period, such as the 12 weeks used in the largest ED trial, and stop if nothing changes. Stop at once and seek care for yellowing skin or eyes, dark urine, sharply reduced urination, a seizure, or an erection that will not go down.