Maca root benefits: what human studies actually measured

Good to know before you start

What the trials reported

• Effects recorded in small trials. In the 2008 pilot, 11 of 16 people analyzed reported at least one, such as stomach upset or headache; the authors called them transient and, as far as they knew, none led anyone to stop. In the 2015 trial, three women stopped because of adverse events such as flu-like symptoms and vomiting, which the authors found hard to attribute to maca.
• The 2024 pharmacology review reports no serious adverse effects at 2 to 3 g a day and very limited information on interactions. It also lists mild stomach upset at about 5 g a day for 30 days in one study, a moderate rise in a liver enzyme (AST) and diastolic blood pressure in a 90-day study of people with metabolic syndrome, and single reports of vaginal bleeding in a woman and a manic episode in a man.

What Memorial Sloan Kettering lists

Memorial Sloan Kettering says in its patient summary that side effects have not been reported; its clinician section lists subjective reports of altered menstrual cycles, moodiness, cramps, gastritis and insomnia. It tells anyone who is pregnant or breastfeeding to talk to a healthcare provider first, and says people with hormone-sensitive cancer should do the same because maca may affect treatment. It notes that, in hypertensive rats, maca strengthened the blood-pressure-lowering effect of losartan (clinical relevance not yet determined).

Other plants on the label, and FDA notices

• Epimedium (horny goat weed). MSK advises avoiding it with heart disease or aromatase inhibitors, and avoiding it or using caution with hormone-sensitive cancers; reported reactions include sweating, rapid irregular heartbeat and mood changes.
• Muira puama. A 2020 review lists impaired memory and reduced locomotion in preclinical studies.
• Ginger. MSK says ginger supplements may raise bleeding risk with blood thinners. On pregnancy, NCCIH and MSK differ; MSK says to avoid supplements and ask first.
• Chili pepper (capsaicin). MSK lists stomach irritation among the side effects, notes interactions with blood-pressure medicines, antiplatelet drugs and immunosuppressants, and says to avoid it in pregnancy and breastfeeding.
• Hidden drugs in some products. A 2026 quality review, as summarized by the American Botanical Council, lists documented adulteration cases for maca: substitution with other powdered roots, spiking with synthetic PDE5 inhibitors and mislabeling of non-Peruvian material as Peruvian. It does not name a product. In a May 2026 notice, FDA reported finding sildenafil and tadalafil, active ingredients of prescription drugs, in a sexual-enhancement supplement that did not list them, and warned that they may interact with nitrates in some prescription drugs and lower blood pressure to dangerous levels. FDA keeps a notifications database of such products.

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