Tribulus is generally considered a safe herbal supplement, and it was actually well tolerated in short-term clinical trials. However, isolated serious reactions are described in the medical literature, and animal husbandry practice knows about the toxicity of the plant for livestock. The editors collected what is known about the side effects of tribulus, how common they are and how to reduce the risks.
What clinical studies say
In randomised trials of tribulus, the incidence of adverse events was generally not different from placebo. For example, in a study by Kamenov et al. (2017) where men with erectile dysfunction took a standardised extract for 12 weeks, the authors separately assessed safety and found no significant differences between groups in terms of adverse events.
In sports studies - Antonio et al (2000), Rogerson et al (2007) - no serious side effects were also reported. These studies lasted five to eight weeks and included healthy young men, limiting the ability to extrapolate the data to other groups.
The problem with clinical trials is that they do not detect rare reactions well. If a serious complication occurs in, say, one of several thousand users, a study of several dozen participants will almost never detect it. This requires pharmacovigilance systems and individual clinical case reports.
It is also important that the studies used specific quality-controlled extracts. Products of different origin, composition and purity are sold on the market, so the safety profile in real life may differ from that recorded in laboratory conditions.
Frequent and mild adverse reactions
Tribulus users often complain of discomfort from the digestive tract. Saponins, which are the main active compounds of the plant, can irritate the mucous membrane of the stomach and intestines. This is manifested by nausea, heartburn, abdominal pain or loose stools, especially when taken on an empty stomach.
- Gastrointestinal symptoms: nausea, heartburn, abdominal discomfort, diarrhoea or constipation.
- Sleep disturbances: Some users report restless sleep and agitation.
- Skin reactions: rash, itching as a manifestation of individual sensitivity.
- Headache and dizziness: reported rarely, without clear dose relationship.
Most of these reactions are mild and resolve after reducing the dose, taking it with a meal, or stopping the supplement. If the symptoms do not disappear or worsen, you should stop taking it and consult a doctor.
Sleep disturbances and agitation have not been systematically described in controlled studies, but appear regularly in reviews. Part of such complaints can be explained not by tribulus itself, but by other components of combined "boosters", for example, stimulants such as caffeine or yohimbine.
It is worth mentioning separately the possible effect on glucose level and blood pressure described in animal studies. No clinically significant changes in controlled studies have been reported in humans, but caution should be exercised in individuals taking hypoglycemic or antihypertensive medications.
Rare serious cases
Several serious clinical cases associated with tribulus intake have been described in the medical literature. They are isolated and do not prove a causal relationship, but are an important signal for doctors and consumers.
| Clinical case | Description | Source |
|---|---|---|
| Nephrotoxicity | Severe kidney damage in a young healthy man after consumption of tribulus decoction | Talasaz et al., 2010 |
| Acute kidney injury and hyperbilirubinaemia | Young man after taking tribulus; kidney damage and increased bilirubin | Ryan et al., 2015 |
| Gynaecomastia | Breast enlargement in a young man taking tribulus | Jameel et al., 2004 |
The case described by Talasaz et al. (2010) is particularly telling: a man who used tribulus as a folk remedy to prevent kidney stones was hospitalized with severe nephrotoxicity. It is interesting that in folk medicine the plant is used precisely for kidney diseases, which once again shows that traditional use does not guarantee safety.
In a case published by Ryan et al. (2015), a young man developed acute kidney injury and markedly elevated bilirubin after consuming tribulus. The combination of kidney damage and liver disorders in this case shows that the plant can affect several organs at once.
Jameel et al.'s (2004) report of gynaecomastia in a young man is paradoxical for a product positioned as a "testosterone booster." The mechanism has not been established, and it cannot be ruled out that the cause was not tribulus itself, but other components of the product.
Toxicity in animals: what it means for humans
In veterinary medicine, tribulus has long been known as a toxic plant for sheep and goats. Liver damage with photosensitization develops in animals when the plant is eaten en masse on pastures, and a neurological syndrome with impaired movement has also been described. These phenomena are associated with plant saponins and alkaloids.
It is not possible to transfer this data directly to people. Sheep eat huge amounts of the fresh plant every day, and humans get a relatively small dose of the extract. In addition, the physiology of ruminant digestion is significantly different from that of humans.
However, toxicity in animals is an argument in favor of the fact that the plant has biologically active compounds capable of affecting the liver and nervous system under certain conditions. Together with isolated cases in humans, this emphasizes that tribulus is not an inert substance.
The practical conclusion is not to exceed the doses used in clinical trials, not to take the supplement continuously for a long time unnecessarily, and to pay attention to any unusual symptoms, including jaundice, dark urine, decreased urine output, or swelling.
Risks related to product quality
Some of the side effects attributed to tribulus may actually be due to the quality of the particular product. Pokrywka et al.'s (2014) review of tribulus supplements for athletes highlights the risk of contamination of products in this category with banned substances, particularly anabolic steroids.
The hidden steroid in the "natural booster" can explain gynaecomastia, suppression of own hormones, and a positive doping test. For the consumer, this is a double danger: he does not know what he is taking, and he cannot assess the risks.
Combination products add their own risks. Stimulants, often included in "testosterone complexes", can cause tachycardia, increased blood pressure and insomnia. In such a situation, it is almost impossible to determine which component caused the reaction.
To reduce risks, choose monoproducts from manufacturers that provide certificates of analysis, and for athletes, products with independent certification for the absence of banned substances, as recommended by the IOC consensus (Maughan et al., 2018).
Editorial conclusions
In clinical studies, tribulus was well tolerated, and the most common adverse reactions were mild gastrointestinal symptoms that resolved after dosage adjustment.
At the same time, single serious cases of damage to the kidneys, liver and gynaecomastia have been described. They are rare, but require careful attention to unusual symptoms and refusal of long-term uncontrolled intake.
A significant part of the risks is determined by the quality of the product: contamination with steroids and stimulants in combined "boosters" can be more dangerous than the plant itself.
We also advise you to familiarize yourself with the materials "Who should not take Tribulus", "Tribulus: forms of release and which one to choose" and "Myths about Tribulus".
List of used literature
- Kamenov Z, Fileva S, Kalinov K, Jannini EA. Evaluation of the efficacy and safety of Tribulus terrestris in male sexual dysfunction â a prospective, randomized, double-blind, placebo-controlled clinical trial. Maturitas. 2017;99:20â26.
- Talasaz AH, Abbasi MR, Abkhiz S, Dashti-Khavidaki S. Tribulus terrestris-induced severe nephrotoxicity in a young healthy male. Nephrol Dial Transplant. 2010;25(11):3792â3793.
- Ryan M, Lazar I, Nadasdy GM, Nadasdy T, Satoskar AA. Acute kidney injury and hyperbilirubinemia in a young male after ingestion of Tribulus terrestris. Clin Nephrol. 2015;83(3):177â183.
- Jameel JK, Kneeshaw PJ, Rao VS, Drew PJ. Gynaecomastia and the plant product "Tribulis terrestris". Breast. 2004;13(5):428â430.
- Pokrywka A, ObmiÅski Z, Malczewska-Lenczowska J, et al. Insights into supplements with Tribulus terrestris used by athletes. J Hum Kinet. 2014;41:99â105.
- 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;10(2):208â215.
- Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439â455.
