Male Infertility

José de Oliveira Vilar Neto et al. (2025) · Nutrients

This systematic review of 10 clinical studies (483 men in total) examined whether Tribulus terrestris supplements improve erectile dysfunction (ED, difficulty achieving or keeping an erection) and testosterone levels. Tribulus is a plant used for centuries in India and China as a sexual stimulant. Its steroidal saponins (plant compounds with hormone-like structure) are proposed to raise testosterone and to boost nitric oxide, a molecule that relaxes blood vessels and supports erections, though the authors note the mechanism is not fully understood. The review asked whether the evidence supports either claim, and it looked at men with and without low testosterone. Researchers searched 13 databases for studies in which men took Tribulus on its own, without other supplements or drugs. Ten studies qualified: nine clinical trials and one study without a control group, conducted in Egypt, Bulgaria, Brazil, Australia, India, China and Spain. Participants were aged 16 to 70: healthy men, men with ED (some also with low testosterone), and men with low sperm counts or unexplained infertility. Doses ran from 400 mg to 12 g per day for 4 weeks to 3 months. Study quality was graded with the Jadad scale, a 5-point checklist of randomization, blinding and dropouts. Three of the five studies that measured erectile function found improvement, and all three enrolled men with ED. One trial using 500 mg daily for 3 months raised International Index of Erectile Function (IIEF-5) scores against placebo, with significance already at 4 weeks (p = 0.0119) and stronger by the end (p < 0.0001). Eight of ten studies found no significant testosterone change, and those men did not have low testosterone at the start. Two studies in men with low testosterone found rises of about 58 to 71 ng/dL (27 to 33%), a small increase in clinical terms (roughly from 215 to 273 and 213 to 284 ng/dL), and both scored poorly for methodological quality (Jadad 2 and 0). None of the studies reported side effects, and lipid and liver tests showed no impairment. The authors conclude that evidence for improved erectile function at 400 to 750 mg per day is of low level and that no solid evidence shows Tribulus raises testosterone. Half of the studies had a high risk of bias, samples were small, saponin content varied between products, and no meta-analysis was possible. The authors state that Tribulus is not a substitute for first-line treatment of severe ED and call for well-controlled randomized trials to define dose and duration, including trials in men with low testosterone.

Gustavo F Gonzales (2011) · Evidence-based complementary and alternative medicine : eCAM

This 2012 review looked at maca (Lepidium meyenii), a root vegetable that has grown in the high Andes of Peru and Bolivia for more than 2,000 years, where it has long been used as both food and a traditional fertility remedy. Written by a Peruvian researcher who has studied maca extensively, the review asked a simple question: does the science actually back up maca's traditional reputation? At the time, Peru's maca exports had grown more than fourfold in a decade, making that question increasingly practical. As a review of existing research rather than one new experiment, there is no single group of people or animals studied. The material available here covers the review's introduction, its round-up of reproduction-focused animal experiments, and its closing remarks, and it leans heavily on rat and mouse studies rather than human trials. How maca is prepared matters: traditional use involves boiling the root or extracting it in alcohol, and the review notes that a simple water extract only works after the pulverized root has been boiled first. In male rats, different doses of maca had inconsistent effects on sexual behavior between two studies, but more reliably increased sperm count and movement, an effect strongest with black maca, weaker with yellow, and absent with red. Red maca extract reduced prostate enlargement caused by testosterone treatment in rats and mice, in a dose-related way, likely due to a plant compound called benzylglucosinolate acting at a step after testosterone's usual hormone receptor rather than by lowering testosterone itself. In female animals, maca did not change estrogen levels but did improve embryo survival in mice, and red and black maca protected bone strength in rats whose ovaries had been removed (a standard aging-and-bone-loss model) without acting like estrogen on the uterus. The review's abstract also states that human clinical trials found maca helpful for sexual difficulties and for sperm count and motility, though the specific numbers behind that claim sit in parts of the original article not available in this record. The author concludes that more chemical and mechanistic research is needed, pointing out that macamides (compounds unique to maca) may explain some of its effects on sexual behavior, though extracts with almost no macamides worked too, meaning other compounds are likely involved as well. Because most of what is captured here comes from animal studies rather than human trials, these findings are best read as promising groundwork pointing toward further human research, useful for understanding why maca is traditionally valued, but not as settled clinical guidance for treating any specific condition today.