Zenico T, Cicero AFG, Valmorri L, Mercuriali M, Bercovich E. Subjective effects of Lepidium meyenii (maca) extract on well-being and sexual performance in patients with mild erectile dysfunction: a randomized, double-blind clinical trial. Andrologia. 2009;41:95-99.

Erectile dysfunction (ED) is defined as the inability to achieve and/or maintain an erection for a duration sufficient to achieve sexual intercourse. The prevalence of ED is estimated to range from 12% to 52%, and the etiology of this disorder is thought to often have a psychological basis that overlaps with a subclinical or clinically identified organic cause. Maca (Lepidium meyenii) root, indigenous to the Andean region, has been purported to have aphrodisiac and fertility-enhancing properties. Limited, although not definitive, evidence indicates the ability of maca to improve sexual function in men. Studies in rodents have shown improvements in epididymal sperm count, improvements in daily sperm production, protection of sperm against toxic agents, and the regression of testosterone-induced prostate hyperplasia. Few studies of the effects of maca in humans have been conducted; however, one observational study noted a significant increase in seminal volume, sperm count, and sperm motility in men who consumed maca daily (1500 or 3000 mg) for 4 months. These findings were confirmed in two 3-month double-blind, randomized controlled trials conducted in healthy men. The objective of the present study was to evaluate the effects of maca root extract on subjective well-being and sexual performance in men with mild ED.

A double-blind, randomized clinical trial was conducted at the Morgagni-Pierantoni Hospital (Forlí, Italy) in 50 young men aged 36 ± 5 years with mild ED [International Index of Erectile Function (IIEF-5) score between 17 and 21] unrelated to a serious psychiatric disorder, medication use, or endocrinologic or cardiovascular disease. The subjects were randomly assigned to treatment with 1200 mg pulverized and dehydrated maca root or placebo tablets twice daily for 12 weeks. The maca tablets were provided by Ibersan Srl (Forlí, Italy). Before and after 12 weeks of treatment, subjective well-being was evaluated with the use of the IIEF-5 and the Satisfaction Profile (SAT-P), and concentrations of follicle-stimulating hormone, luteinizing hormone, prolactin, and total and free testosterone were measured. A P value <0.05 was considered to indicate a significant difference.

IIEF-5 and SAT-P scores were not significantly different between the 2 groups at baseline. After 12 weeks of treatment, the IIEF-5 score increased significantly in both groups; however, the increase in the maca group (1.6 ± 11) was significantly greater (P < 0.001) than the increase in the placebo group (0.5 ± 0.6). Similarly, the SAT-P score for psychological performance improved significantly in both the maca group and the placebo group after 12 weeks of treatment, but significantly more so (P < 0.05) in the maca group (+9 ± 6) than in the placebo group (+6 ± 5). However, the SAT-P score for physical performance and for social performance improved significantly (+7 ± 6 for both; P < 0.05) only in the maca group. SAT-P scores for cognitive and professional performance did not change significantly in either treatment group after 12 weeks of treatment. None of the hormone concentrations measured changed significantly after treatment in either of the 2 groups.

The results support "a small but significant effect of maca supplementation on subjective perception of general and sexual well-being in young adult patients with mild ED." The maca-induced improvement in IIEF-5 scores appeared to be inversely related to the baseline IIEF-5 score. The study was limited by its small sample size, which would likely limit chances of observing a possibly greater efficacy of maca in patients with more serious ED. An additional limitation was the relatively short duration of the trial, which may have prevented observations of the maximal achievable effects of maca. Because it is assumed that maca affects the central nervous system and because the perception of well-being is strongly associated with sexual performance, the authors conclude that it is difficult to definitively determine whether maca exerts its activity on erectile function per se, centrally, or both.