Maca is the dried hypocotyl of Lepidium meyenii, a crucifer grown above 4,000 meters in the Peruvian Andes and eaten there as a food. Its reputation as an aphrodisiac and fertility aid is old, and the first controlled trials came from a Peruvian group in the early 2000s.

What makes it interesting on a shelf full of testosterone claims is that its own trials rule testosterone out. In the same 12-week trial that found improved sexual desire, serum testosterone and estradiol did not move, and a companion study found no change in LH, FSH, prolactin or any other reproductive hormone. If maca does something for desire, and the trials are small, it does it some other way.

Maca contains macamides and macaenes, unusual fatty-acid amides that are the constituents most studied, plus glucosinolates and alkaloids. Proposed actions include effects on central neurotransmission and on energy metabolism rather than on sex hormones, which fits the trial finding that desire improved while hormones stayed flat. A 2024 meta-analysis of animal and human work attributed its physical-performance effects to the macamides, with a dose-response. The human mechanism has not been identified.

Sexual desire. The 2002 Peruvian trial gave men aged 21 to 56 1,500 mg or 3,000 mg of gelatinized maca or placebo for 12 weeks: self-reported sexual desire improved from week eight, independently of depression and anxiety scores and of testosterone and estradiol, which did not change. The 2003 companion study measured LH, FSH, prolactin, 17-hydroxyprogesterone, testosterone and estradiol at five time points and found no effect on any.

Erectile function. Fifty men with mild erectile dysfunction took 2,400 mg of dry extract or placebo for 12 weeks. IIEF-5 rose in both groups, more on maca (1.6 against 0.5 points), with better psychological, physical and social well-being scores. A 1.6-point gain is small.

Antidepressant sexual side effects. A pilot in 20 patients, 17 of them women, with SSRI-induced sexual dysfunction found 3.0 g a day improved sexual function scores and 1.5 g did not. Half completed.

Reviews. A 2010 systematic review found four randomized trials and called the evidence for sexual function limited, with trials too few, too small and too weak to draw firm conclusions. A 2016 review of semen quality found three randomized trials and two uncontrolled studies pointing the right way and reached the same verdict.

Fertility. A 2021 placebo-controlled trial in 50 infertile men over 16 weeks found no significant effect on sperm concentration (the placebo group improved more) and no hormone change except a fall in free testosterone.

Performance. A 2024 meta-analysis of 21 studies, mostly in animals, found large effects on forced swimming, rotarod and grip strength; the human evidence inside it is thin.

Maca is a food in Peru and the trials report it as well tolerated at up to 3 g a day for 12 to 16 weeks, with no adverse effects noted. The infertility trial's fall in free testosterone is the only unwelcome signal in the file and was not significant for the trial's main outcome.

It is a crucifer, so it carries glucosinolates, which in large amounts can interfere with thyroid function in people short of iodine; the trials did not look. No drug interactions are reported, but no study has looked for those either.

A food and a dietary supplement in the United States and the United Kingdom. In the European Union maca was on the market before the novel-food rules, so it is sold freely as a food. No regulator has approved any libido, fertility or hormone claim, and the trials would not support a hormone claim in any case.