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Tribulus terrestris is an interesting herb plant which has been well-known for its abilities to treat urinary stones, Parkinson’s disease, along with its unique capacity to treat liver and eye disease and improve sexual and physical strength [1; 2]. In addition, tribulus has been widely used as a main constituent for synthesis of many medicines and food supplements, where it has been associated with being a therapeutic agent for the cardiovascular system and immune system . Tribulus terrestris fruit is also known for its aphrodisiac properties, which has been shown in previous animal laboratory studies [4; 2].
How does Tribulus terrestris work
Tribulus terrestris contains many important compounds, such as steroids, saponins, flavonoids, alkaloids, unsaturated fatty acids, vitamins and glutamic acid . In particular, Tribulus methanol extract contains inositol, palmitic acid, estradiol, linoleic and stearic acid  –Figure 1. Extracts of tribulus are known to contain antioxidant, anti-apoptotic, anti-hypertension, anti-diabetic, anti-cancer and anti-fungal properties . Moreover, methanol tribulus extract possess anti-inflammatory and analgesic effects; alkaloid-enriched tribulus extract diminished diabetes-induced neuropathic pain . Recently, a methanol extract of tribulus was found to contain a new compound, cis-terrestriamide, which exhibited inhibitory effects on nitric oxide production in a cell line .
Benefits and Effects
Tribulus has a traditional history of use in for problems linked to the musculoskeletal, urogenital, gastrointestinal and central nervous systems . Along with these amazing benefits throughout the human physiology, tribulus is also known to contain antibacterial, antifungal and anti-inflammatory effects . Fruit extracts of tribulus have also been shown to have an effective antioxidant and anti-inflammatory response to a human colorectal carcinoma cell line . Extracted air-dried aerial parts of tribulus contains mainly steroidal glycosides, with the major saponin being protodioscin (PTN) (Figure 2) . In this regard, PTN has been hailed as the pharmacologically active compound/ingredient of tribulus terrestris, with all other compounds being [pharmacologically] inactive [8; 10].
Tribulus terrestris depression
A study assessing the anti-depressive role of tribulus saponins on behaviour in mildly depressed rats, showed that tribulus – at a low, medium and high – had anti-depressive effects . More recently, a 400mg dose of methanol extract of tribulus was shown to have anti-depressant properties; this was highlighted through the restoration of antioxidants such as catalase, superoxide dismutase and malondealdehyde . In addition, an ethanol tribulus extract at a dosage of 100, 300 and 500mg/kg possessed adaptogenic (anti-stress) activity . The stress tests included anoxia (severe form of stress) and tribulus was able to normalise stress biomarkers – i.e. decreases in blood glucose, cholesterol and triglycerides . In assessing the effects of tribulus in menopausal transition symptoms in women, researchers found tribulus to reduce psychological and urogenital symptoms of menopausal transition . Looking further, tribulus was observed to improve depressive symptoms with a 68.8% improvement . Interestingly, tribulus contains the alkaloid Harmine, which is noted as being an irreversible Monoamine Oxidase A (MAOI-A) inhibitor . This inhibition of Monoamine oxidase-A means that serotonin (5-HT) and other monoamines in the brain evade oxidative metabolism . As a result, this leads to mood changes; the alleviation of depression . Authors of this work note the need to carry out further investigations to evaluate the benefits of tribulus.
Tribulus terrestris blood pressure
Tribulus has been documented as treating high blood pressure . Dry, aqueous tribulus extracts – dosage of 500mg of capsule form – were administered to patients suffering from Grade I essential hypertension . Significant improvements were noted in systolic and diastolic blood pressure after 14 and 28 days, respectively . Authors also noted that tribulus may be safe and effective in managing hypertension; however, recommend further large-scale experiments be carried out .
Tribulus terrestris libido
Administration of tribulus terrestris to humans has been reported to improve libido and spermatogenesis . Also, since tribulus terretris is a naturally occurring traditional plant herb, it has been known to enhance sexual activites , as well as treating sexual dysfunction [Chauhan et al., 2018]. Work seeking to better describe the efficacy of tribulus terrestis on sex hormones to grasp tribulus’s possible usefulness in treating erectile dysfunction (ED), demonstrated an increase in testosterone and DHT (dihydrotestosterone) . Indeed, this work suggested the active role of PTN – the presence of this steroidal glycoside . Dosage of tribulus extract for erectile dysfunction (ED) has been described as 400mg capsules ; this dose was taken twice in one day .
Tribulus for men and women
Tribulus terrestris has also been reported to induce sexual arousal and desire in women . A qualitative/quantitative study addressed the role of tribulus terrestris in treating female sexual dysfunction and found increased levels of DHEA (dehydroepiandrosterone), along with decreases in serum and free testosterone . In men, evidence suggests that tribulus can improve erectile dysfunction (ED) and sexual desire . A dry, ethanol-derived extract of tribulus terrestris given to female and male rats in an experiment to assess effects on endocrine sensitive organs . This work showed that tribulus was not able to stimulate endocrine sensitive tissues: prostate, uterus and vagina in male and female rats. Thus, tribulus was concluded as lacking androgenic and estrogenic activity .
Tribulus terrestris kidney stones
Research reports that tribulus fruits extract taken regularly for a fortnight, can help expel kidney stones. Remarkably, tribulus extract has been shown to inhibit the growth of calcium oxalate (CaOx) crystals . In this work, researchers used a tribulus powdered fruit extract at varying concentrations to test its inhibition properties on calcium oxalate. Figure 3 graphically describes the dose-dependent inhibition on CaOx. Calcium oxalate stones are the most common type of kidney stone; and, these occur when there are high levels of calcium and oxalate. Calcium oxalate crystals occur when there is a disproportionate ratio of urine waste to liquid. Too much waste in one’s urine ultimately results in in formation of crystals. These crystals stick together and form the well-known kidney stone. Another in vivo study addressed tribulus’ effect in renal tissue after induction of hyperoxaluria . Hyperoxaluria is a condition with characteristic recurrent kidney and bladder stones. Consequence of this condition is progression to end stage renal disease (ESRD); a life-threatening condition. Tribulus was able to reduce oxalate, calcium and phosphate excretion; along with reducing hyperoxaluria-related oxidative stress . Lastly, tribulus aqueous extract was able to restore antioxidant enzyme activity in the kidney tissue .
Tribulus and tongkat ali
Tongkat ali (Eurycoma longifolia) is said to possess anti-stress and anti-disease properties, and to improve physical strength . Additionally, compounds derived from the root of this herbal medicine, just like tribulus, have been reported to have effects on testosterone and sexual drive . Tongkat ali contains peptides known as ‘eurypeptides’, which are noted as improving sex drive and energy in animal studies . Oral Lethal Dose 50 (LD50) of E. longifolia has been suggested at between 1500-2000mg/kg; with oral LD50 being more than 3000mg/kg .
Side effects of Tribulus terrestris
Although safety has been reported in the use of tribulus extract, there has been one reported case – male patient – who after consuming tribulus terrestris showed acute kidney injury, hepatitis and seizure . There is some debate as to whether tribulus actually has testosterone boosting properties; this has been widely argued on open source forums where tribulus users over the age of 30 have often reported effects on muscle gain and increased libido – from increases in testosterone . Also, studies on tribulus’ impact on atheletes confirmed that although tribulus had extra physiological benefits, it did have a negative effect on red blood cells, haemoglobin and thrombocyte indicies . It has been recommended that athletes who consume tribulus at 25mg per 10kg body mass undertake complete blood counts (CBC) .
Established, effective tribulus dose – 1 capsule (625mg powder), 3 times a day for 20 days – was reported as statistically increasing physical power in athletes . In addition, it has been found that blood testosterone levels increased after 10 days of experimental administration of tribulus [Milasius et al., 2009], along with anaerobic alactic glycolytic power increases. Tribulus was administered in tablet form – in a concentration of 250mg . Oral toxicological doses of tribulus have demonstrated that a chronic aqueous extract of tribulus did not yield any adverse effects in mice subjects . Safe doses of tribulus (as homeopathic agents) in concentrations of 4mL per kg, have been found in 28-day long toxicity studies – no changes were noticed on biochemical, haematological and histological parameters .