Erectile Dysfunction

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.

Dongho Shin et al. (2023) · The world journal of men's health

This randomized, double-blind, placebo-controlled trial with 80 men explored whether Maca (Lepidium meyenii), a root vegetable traditionally grown high in the Peruvian Andes and eaten as a nutritional "superfood," can ease late-onset hypogonadism (LOH), the cluster of low-testosterone-type symptoms, such as fatigue, low mood, reduced libido, and erectile difficulty, that many men develop with age even when their blood testosterone level is technically normal. Because standard testosterone replacement therapy carries cardiovascular and prostate-cancer risks, researchers wanted to know whether Maca, long used as a folk aphrodisiac and fertility aid, could offer relief without those risks. Eighty men over 40, recruited as outpatients at two South Korean hospitals and randomly split into two groups, took either 1,000 mg Maca tablets or an identical-looking placebo, two tablets three times a day before meals (about 5 grams of Maca daily), for 12 weeks. Neither the men nor the study staff knew who was getting the real supplement. Researchers tracked symptoms with four standard questionnaires covering overall aging-male symptoms, androgen deficiency, erectile function, and urinary symptoms, and ran blood tests for testosterone, cholesterol, and other safety markers at baseline, 4 weeks, and 12 weeks. Only the Maca group showed real improvement: overall symptom scores dropped by nearly 11 points from baseline (p<0.0001), while placebo barely moved (statistically unchanged, p=0.5007), and the difference between groups was highly significant (p<0.0001). Androgen-deficiency screening flipped from mostly positive to mostly negative in the Maca group (70.7% down to 56.1% at 12 weeks, p<0.0001 versus placebo). Erectile function scores rose by 14 points with Maca (p<0.0001, meaning a clear improvement) while the placebo group's scores actually fell, and urinary symptom scores improved with Maca too (p=0.0025) with no such change on placebo. Notably, none of this tracked with testosterone levels, which barely budged in either group, suggesting Maca works through some other pathway the study did not pin down. Only two participants reported mild stomach upset, and no serious safety issues turned up in blood work or vital signs. In men who were not candidates for testosterone therapy, this study found Maca well tolerated, with its effects on sexual and urinary symptoms rather than on lab-measured testosterone itself. The trial ran only 12 weeks, so it cannot say whether benefits last, and every participant was Korean, so results may not generalize to other populations. The researchers themselves flag that the biological mechanism behind Maca's effect is still unknown and call for longer, more mechanistic follow-up studies.

Norka Ulloa Del Carpio et al. (2024) · Frontiers in pharmacology

This 2024 review pulled together the science on maca (Lepidium meyenii), an Andean root long eaten as food and used as a traditional remedy. Maca's chemical makeup varies with the plant's ecotype, growing conditions, and processing, giving rise to a complex mix of bioactive compounds called macamides, macaenes, and glucosinolates. Rather than running one new experiment, the authors gathered evidence from lab studies, animal research, and human clinical trials to map out what science currently knows, and does not yet know, about maca's effects and safety. Because this is a literature review rather than a single study, there is no one group of participants or one experimental design to describe. Instead, the authors drew on a mix of test-tube studies, rodent experiments, and human trials identified across the maca research, including safety data submitted for the United States Pharmacopeia's evaluation of maca as a dietary ingredient for the National Formulary, covering root powder, gelatinized powder, and various purified extracts sold as supplements. The review's central finding is that maca appears to act as an adaptogen (a substance that helps the body handle stress) by influencing the hypothalamus-pituitary-adrenal axis (the body's central stress-response system), likely through macamide compounds working via serotonin and cannabinoid-receptor pathways. Lab and animal studies point to neuroprotective, anti-inflammatory, and antioxidant effects, including in models of prostate enlargement and lung and liver inflammation. In humans, the review describes maca research as concentrated on sexual health, with reported improvements in sexual desire, erectile function, and general wellbeing in men, plus some evidence for easing menopausal symptoms in women and improving physical performance, though the review does not provide the specific numbers behind these findings. Safety testing found generally low toxicity, though a small number of people reported side effects such as stomach upset, headache, and irritability, and rare reports of vaginal bleeding or a manic episode. The authors are candid that inconsistent study designs, doses, and treatment lengths across the maca research make results hard to compare directly, and they call for more standardized studies to pin down maca's mechanisms and confirm its benefits before firmer guidance can be offered. This review is best read as a map of where maca's promising leads are, especially sexual health and neuroprotection, rather than as proof of any specific effect on any one condition.