Benefits
Sexual Function and Desire
In 50 men with mild erectile dysfunction, 2,400 mg a day of maca extract for 12 weeks raised erectile function scores slightly more than placebo (1.6 vs 0.5 points). In 8 cyclists, 14 days of extract raised self-rated sexual desire versus placebo. In 45 women with antidepressant-related sexual problems, 3 g a day gave numerically higher remission rates than placebo. All were small trials.
Semen Quality
Results are mixed. In a 12-week pilot trial in 69 men with mildly low sperm count or motility, 2 g a day raised sperm concentration versus placebo but not motility, volume or shape. In 50 men with fertility problems, 16 weeks of yellow maca did not differ from placebo. An uncontrolled study in 9 healthy men reported higher sperm count and motility. No trial measured pregnancy rates.
Menopausal Symptom Scores
A 2011 systematic review found 4 randomized trials, all reporting favourable menopause symptom scores, but the authors concluded they provide limited evidence because the trials were few, small and of modest quality, and noted that safety had not been established. In a trial in 14 postmenopausal women, maca did not change estradiol, FSH or LH.
Mood in Postmenopausal Women
In a crossover trial in 14 postmenopausal women, 3.5 g a day for 6 weeks lowered the anxiety, depression and sexual dysfunction subscale scores of a menopause symptom scale compared with placebo, without changing estradiol, FSH, LH or SHBG. Fourteen women is a very small sample, and maca is not a treatment for depression or anxiety.
Cycling Time-Trial Performance
In 8 trained male cyclists, 14 days of maca extract improved 40 km time-trial times compared with their own baseline but not compared with placebo, so it showed no performance benefit in the comparison that matters. Eight people is far too few to draw conclusions.
Aging Male Symptom Scores in Men Over 40
In 80 Korean men over 40 with normal testosterone but symptoms of late-onset hypogonadism, two 1,000 mg capsules of gelatinized maca three times a day (about 5 g of maca powder daily) for 12 weeks improved aging-male symptom, erectile function and urinary symptom scores more than placebo. Total and free testosterone did not differ from placebo.
Mechanism of action
Antioxidant and Anti-Inflammatory Effects
Glucosinolates and flavonoids scavenge free radicals in laboratory tests, and glucosinolate breakdown products affect inflammatory signalling in cell and animal experiments. None of the human trials cited here measured oxidative stress or inflammation, so whether this matters in people is unknown.
Neuroendocrine Effects (Proposed)
Maca contains fatty acid derivatives called macamides that are chemically similar to the body's own endocannabinoid compounds, and researchers have proposed they act on stress and mood pathways. That is a hypothesis from laboratory work. No human trial cited here measured HPA axis activity or cannabinoid receptors, so this remains an idea rather than a demonstrated mechanism.
Effects on Sperm Production
Maca's effect on sperm has no established mechanism. Animal work has suggested protection of testicular tissue from oxidative damage, but the human semen studies measured semen parameters and hormones, not mechanisms, and found no change in LH, FSH or testosterone in healthy men.
Maca Is Not an Estrogen
Maca does not appear to act as an estrogen. In a trial in postmenopausal women, it did not change estradiol, FSH, LH or SHBG, and maca extracts showed no meaningful estrogenic or androgenic activity in yeast-based laboratory assays. How maca might ease menopausal symptoms is not known.
Energy and Performance (Proposed)
Claims that maca improves mitochondrial efficiency, glucose metabolism, endurance or muscle recovery come from laboratory work. The one exercise trial cited here, in 8 cyclists, did not beat placebo, so there is no human result for this mechanism to explain.
Clinical trials
12-week randomized double-blind placebo-controlled trial of 2,400 mg maca dry extract a day. (Zenico et al. 2009, Andrologia)
50 Caucasian men with mild erectile dysfunction.
IIEF-5 erectile function scores rose in both groups, but more with maca (1.6 vs 0.5 points, P < 0.001). Psychological well-being scores also improved more with maca, and physical and social well-being improved only with maca. The authors described a small but significant effect.
12-week double-blind placebo-controlled trial of 3.0 g/day maca root. (Dording et al. 2015, Evid Based Complement Alternat Med)
45 women (mean age 41.5) with SSRI or SNRI-related sexual dysfunction whose depression was in remission; 42 analyzed.
Remission rates on sexual function questionnaires were numerically higher with maca than placebo (for example 30.0% vs 20.0% on one scale), and the difference was attributable to the 12 postmenopausal women. Maca was well tolerated.
Double-blind randomized parallel-group pilot comparing 1.5 g/day with 3.0 g/day maca, without a placebo group. (Dording et al. 2008, CNS Neurosci Ther)
20 outpatients with remitted depression (17 women, mean age 36); 16 analyzed, 10 completed.
Sexual function scores improved from baseline on 3.0 g/day but not on 1.5 g/day, and libido improved in the group overall. With no placebo group and 10 completers, this cannot separate a maca effect from placebo response.
Systematic review of randomized placebo-controlled trials of maca for menopausal symptoms, searched to June 2011. (Lee et al. 2011, Maturitas)
4 randomized trials in healthy perimenopausal and postmenopausal women.
All 4 trials reported favourable effects on the Kupperman Menopausal Index or Greene Climacteric Scale, but the authors concluded the evidence was limited because of the small number of trials, small total sample size and modest quality, and said safety had not been established.
4-month open-label study of maca tablets at 1,500 or 3,000 mg/day, with no placebo group. (Gonzales et al. 2001, Asian J Androl)
9 healthy adult men aged 24 to 44.
Semen volume, sperm count, motile sperm count and motility increased, while LH, FSH, prolactin, testosterone and estradiol did not change. The rise in sperm count was not related to dose. Without a control group, chance or normal variation cannot be ruled out.
12-week double-blind randomized placebo-controlled pilot trial of 2 g/day maca. (Alcalde et al. 2020, Andrologia)
69 men with mild asthenozoospermia and/or mild oligozoospermia (35 maca, 34 placebo).
Sperm concentration was higher with maca than placebo (mean 15.04 vs 10.16, p = 0.011). Semen volume, sperm motility and normal morphology did not differ.
16-week randomized double-blind placebo-controlled trial of yellow maca. (Melnikovova et al. 2021, Phytother Res)
50 men with various reproductive problems.
Sperm concentration rose 40% with maca and 76% with placebo, and neither change differed significantly between groups. Hormones did not change except a fall in free testosterone. The authors said the results are not sufficient to judge maca for male fertility.
Randomized crossover pilot of 14 days of maca extract versus placebo. (Stone et al. 2009, J Ethnopharmacol)
8 trained male cyclists.
40 km time-trial times improved versus baseline (P = 0.01) but not versus placebo. Self-rated sexual desire improved versus both baseline and placebo (P = 0.03). Very small sample.
12-week randomized double-blind placebo-controlled trial of two 1,000 mg capsules (833 mg gelatinized maca each) three times a day; the full text lists support from the Korea Medical Device Development Fund. (Shin et al. 2023, World J Mens Health)
80 Korean men over 40 with normal testosterone and symptoms of late-onset hypogonadism (41 maca, 39 placebo).
Aging Males' Symptoms, erectile function (IIEF) and urinary symptom (IPSS) scores improved more with maca than placebo. Total and free testosterone did not differ between groups.
Randomized double-blind placebo-controlled crossover trial of 3.5 g/day powdered maca for 6 weeks. (Brooks et al. 2008, Menopause)
14 postmenopausal women.
Greene Climacteric Scale scores for psychological symptoms (including anxiety and depression) and sexual dysfunction fell compared with baseline and placebo. Estradiol, FSH, LH and SHBG did not change. Very small sample.