Evidence Review
Libido and Sexual Function
The most robust human evidence for maca concerns sexual desire. A 2002 randomized, double-blind, placebo-controlled study (n=57 men) by Gonzales et al. found that maca at 1.5 g or 3 g per day for 8 weeks significantly increased subjective sexual desire compared to placebo (p<0.01), with the effect appearing at week 8. Critically, testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, and estradiol were measured and showed no significant changes — demonstrating that the libido effect operates independently of classic sex hormone pathways [1].
A 2010 systematic review by Shin et al. identified four placebo-controlled RCTs (n=131 participants total) examining maca and sexual function. The review concluded there was "limited evidence" for effectiveness, with two trials showing significant improvements in sexual dysfunction and desire, and two showing no significant effect. The heterogeneity in study design, populations, and doses made firm conclusions difficult [3]. The authors noted that the positive trials used higher doses (2–3 g/day) and longer durations (≥8 weeks), suggesting dose and time are critical variables.
SSRI-Induced Sexual Dysfunction
Two trials from Harvard Medical School (Dording et al.) specifically tested maca in patients whose sexual function was impaired by antidepressant medication. In the 2008 pilot study (n=20), both 1.5 g and 3 g/day doses were compared; the 3 g group showed significant improvement in sexual function scores on the Arizona Sexual Experience Scale (ASEX), while the 1.5 g group did not reach significance [6]. The 2015 follow-up RCT (n=45 women on SSRIs or SNRIs) found that 3 g/day maca outperformed placebo on remission rates (sexual function returning to normal) across multiple validated measures of desire, arousal, and orgasm [5]. These findings are clinically relevant given how common SSRI-related sexual side effects are.
Menopausal Symptoms
A 2011 systematic review by Lee et al. identified three RCTs examining maca for menopausal symptoms (hot flashes, night sweats, mood, sleep, fatigue). All three trials reported improvements on the Greene Climacteric Scale or Kupperman Menopausal Index compared to placebo. The reviewers classified the evidence as "promising but preliminary," limited by small sample sizes (total n=112 across all trials) and short durations of 6–12 weeks [4]. A notable feature across trials was that maca improved FSH levels — which are elevated in menopause — without changing estrogen or progesterone, again pointing to a central regulatory effect rather than direct estrogenic activity.
Hormone Levels: What Maca Does and Does Not Do
Multiple studies have measured hormone levels before and after maca supplementation in both men and women. The consistent finding is that maca does not significantly alter serum testosterone, estradiol, FSH, LH, or prolactin in healthy adults [1][2]. This distinguishes maca from herbs like DHEA or phytoestrogens (soy isoflavones), which directly influence hormone receptor activity. The implication is that maca's benefits are unlikely to carry the risks associated with hormone-active compounds — though this also makes its mechanism harder to pin down.
Limitations and Evidence Quality
The overall quality of maca research is modest. Most trials are small (n=20–60), short (6–12 weeks), and conducted by a limited number of research groups. Publication bias toward positive results is possible. There are no large multi-center trials or long-term safety studies beyond 12 weeks. Animal data is considerably more extensive, but species differences (particularly around black maca's effects on sperm count) do not always translate to humans. Maca appears safe at food-equivalent doses (1–3 g/day), with no significant adverse effects reported in trials, though thyroid-active compounds in raw maca (glucosinolates) suggest caution for people with thyroid disease — gelatinized maca reduces this concern.