Maca root is generally well tolerated, but it can cause digestive upset, headaches, insomnia, and jitteriness in some people. Beyond those common complaints, maca carries less obvious risks related to hormonal activity, thyroid function, and heavy metal contamination that are worth understanding before you add it to your routine.
Common Side Effects
The side effects most people report from maca are mild and digestive: bloating, gas, stomach cramps, or loose stools. These tend to show up when you start taking maca or increase your dose, and they often settle down after a few days as your body adjusts. Taking maca with food rather than on an empty stomach can help.
Some users also experience headaches, difficulty sleeping, and a jittery or overstimulated feeling similar to drinking too much coffee. Maca doesn’t contain caffeine, but it has a reputation as an energizing supplement, and that stimulating quality seems to affect some people more than others. If you notice sleep disruption, taking maca in the morning rather than the evening is a simple fix.
Hormonal Effects
Maca has measurable estrogenic activity in lab studies, meaning it can mimic or amplify the effects of estrogen in certain tissues. In real-world use, the hormonal picture is more nuanced. Studies in men show that maca does not change blood levels of testosterone, estrogen, or other reproductive hormones. In women, the results are mixed: some studies find that maca shifts hormone levels (particularly lowering follicle-stimulating hormone in postmenopausal women), while others find no measurable hormonal change at all.
This matters most if you have a condition that’s sensitive to estrogen. Memorial Sloan Kettering Cancer Center specifically warns that people with hormone-sensitive cancers, such as breast or uterine cancer, should talk to their doctor before using maca because it may interfere with treatment. The same caution applies if you have endometriosis or uterine fibroids, both of which can be driven by estrogen. Even though maca’s hormonal effects in humans are inconsistent across studies, the lab evidence of estrogenic activity is enough reason to be cautious.
Thyroid Concerns
Maca belongs to the cruciferous vegetable family, alongside broccoli, kale, and cabbage. Cruciferous plants contain compounds called glucosinolates that can, in large amounts, interfere with the thyroid gland’s ability to use iodine and produce hormones. This is mostly a theoretical concern at normal serving sizes. You’d likely need to consume very large quantities of maca for this to become a real problem. But if you already have an underactive thyroid or are taking thyroid medication, it’s worth knowing that maca could add one more variable to the equation.
Heavy Metal Contamination
Maca is grown almost exclusively in the highlands of central Peru, and some of that farmland sits near active or former mining sites. A study analyzing maca grown in the JunÃn province found that average concentrations of both cadmium and lead in the edible root exceeded limits set by the World Health Organization and the Food and Agriculture Organization. Soil samples from the same region showed lead levels more than 70 mg/kg, far above national safety standards.
The researchers found that while the non-cancer health risk from these metals was below the threshold for concern, the estimated cancer risk from arsenic and cadmium exposure exceeded tolerable limits for both children and adults. This doesn’t mean every bag of maca powder on the shelf is contaminated, but it does mean the source matters. Maca is sold as a supplement, so it isn’t subject to the same testing requirements as conventional food. If you use maca regularly, choosing a product that provides third-party testing for heavy metals is one of the most practical steps you can take.
Dosage and Safety in Studies
Most clinical trials have used between 1,500 and 3,000 mg of maca powder per day, taken in divided doses with meals, for periods of 6 to 12 weeks. A randomized, placebo-controlled trial published in the World Journal of Men’s Health used 3,000 mg daily for 12 weeks and reported no serious adverse events. Across the broader clinical literature, serious side effects from maca are essentially absent at these doses.
That said, the supplement aisle often sells maca in concentrated extract form, where a single capsule may deliver the equivalent of several grams of raw powder. If you’re using a concentrated product, the effective dose you’re taking could be much higher than what was tested in studies. Starting at the lower end of the range and increasing gradually gives you a chance to notice any sensitivity before committing to a full dose.
Who Should Be Cautious
Most healthy adults can take maca without problems, but a few groups should pay extra attention. People with hormone-sensitive conditions, including breast cancer, uterine cancer, endometriosis, and fibroids, should avoid maca or discuss it with their oncologist or gynecologist first. People with thyroid disorders, especially hypothyroidism, should be aware of the cruciferous connection and monitor their thyroid levels if they decide to use it. And anyone taking maca long-term should prioritize products that have been independently tested for heavy metals, particularly lead and cadmium, given the contamination data from Peruvian growing regions.