Maca Side Effects and How Much to Take: What the Trials Used

In placebo-controlled trials of 45 to 175 people taking 2.8 g to about 5 g of maca a day for up to 16 weeks, no serious side effects were recorded, and a few people had stomach upsets or stopped early.^{1, 2, 3, 4} Outside the trials sit three single case reports: lead in one powder, a falsely high testosterone test and liver injury after a maca liquor.^{5, 6, 7}

A PubMed search on 13 October 2026 found no drug-interaction study of maca in people. Maca is a food, not a novel food, in Great Britain.⁸ The NHS herbal medicines advice is the nearest guide: not in pregnancy, while breastfeeding or with kidney or liver problems, and a pharmacist first if you take medicines.⁹

Evidence at a glance

• Trials: side effects recorded in 5 placebo-controlled trials of about 12 to 16 weeks; three case reports.
• Largest single trial: 175 adults, 3 g of maca extract or placebo daily for 12 weeks; no serious side effects.
• Strongest measured outcome: in 80 men taking about 5 g a day for 12 weeks, blood, urine, blood pressure and PSA tests showed no clinically significant change.
• Not tested: pregnancy, breastfeeding, children, a drug-interaction study, or use beyond about eight months.

Sources checked on 14 October 2026.

What side effects did the maca trials record?

Few, and none serious. In the largest trial, dropouts were similar on maca and placebo.⁴

What do the maca case reports describe?

In the US, a woman's blood lead rose after she began a maca root powder and fell when she stopped.⁵ The NHS notes some herbal products may contain lead, so batch testing for heavy metals matters.¹¹ In the UK, a woman taking maca extract read 25.8 nmol/l for testosterone on one test method and 2.9 nmol/l when the sample was rerun on another.⁶ In China, a man developed jaundice after one 300 ml drink of maca liquor at 50% alcohol.⁷ The US reference LiverTox says maca "has not been implicated in causing liver injury".¹² If skin or eyes turn yellow, the NHS says ask for an urgent GP appointment or get help from NHS 111.¹³

How much maca did the trials use?

From 0.6 g to about 5 g a day: 3 to 3.5 g of root powder, 1.5 to about 5 g of gelatinised root and 2.4 to 4.5 g of extract.^{1, 2, 3, 4, 10, 14, 15, 16, 17, 18} Andean diets include more than 20 g of dried root a day, boiled.¹⁹ These are amounts studied, not a recommended dose.

Labels state maca two ways. Powder and gelatinised root are weighed as root. An extract label's "equivalent to" figure is the weight of dried root the extract was made from, not the weight in the capsule, and ratios differ: 200 mg of a 10:1 extract is "equivalent to 2,000 mg". Compare root equivalents with root and powder trials, extract weights with extract trials. Forms are on black, red and yellow maca; the men's amounts on maca for men.

When should you take maca, and what can you take it with?

No trial compared morning with evening. The 80-man trial gave capsules before food three times a day; a supplier-linked trial gave them with meals twice daily.^{1, 20} Desire scores in men differed from placebo from week 8; no trial measured same-day effects.¹⁴

In a laboratory test of 29 herbal supplements, maca inhibited CYP3A, an enzyme that handles many medicines, by under 50%, against over 80% for the strongest.²¹ One of 1,816 adverse-event reports in people on antidepressants involved maca: restless legs with mianserin.²² In one trial, women on SSRI or SNRI antidepressants took 3 g a day and the authors found it well tolerated (libido supplements for women has its results).³ The NHS lists statins, antidepressants, diabetes and blood pressure medicines, blood thinners and hormonal contraception as not mixing well with herbal medicines: check with a pharmacist first.⁹ No trial has tested maca with ashwagandha or magnesium; see who should not take ashwagandha.

Who should not take maca, or should ask a GP or pharmacist first?

The NHS says not to take herbal medicines if "you're pregnant or breastfeeding", "you have kidney or liver problems" or "you're taking certain medicines from a pharmacy or doctor", and that they "are not recommended for children".⁹ The 80-man trial excluded kidney disease and markedly raised liver enzymes.¹ Diastolic blood pressure fell in 29 postmenopausal women, rose in the 0.6 g study and did not change in the 80 men, so anyone treated for blood pressure asks first.^{1, 10, 23}

Can you take maca in pregnancy, while breastfeeding, or with a thyroid or hormone-sensitive condition?

No maca trial included pregnant or breastfeeding women. The NHS says: "You're also advised not to take herbal remedies if you're trying to get pregnant," and "Tell your midwife, doctor or pharmacist if you're using herbal, homeopathic or aromatherapy remedies or therapies."¹¹

Maca is a cabbage-family plant containing glucosinolates.¹⁹ Thyroid-stimulating hormone did not change in 29 women over 6 weeks; T3, a thyroid hormone, was lower after two months in one supplier-linked trial of 34 women.^{20, 23} Oestradiol did not change in the 29 women but rose in the supplier-linked trial, and no trial enrolled anyone with a hormone-sensitive condition.^{20, 23} With a thyroid or hormone-sensitive condition, a GP comes first.

What happens if you take maca every day, and when you stop?

The trials gave maca daily, for 6 to 16 weeks. The longest record is a supplier-linked programme in which 8 women took 2 g of gelatinised maca a day for eight months of a nine-month programme.²⁴ No study has run longer or examined stopping. The Wellgard maca guide covers what the trials measured.

What we don't know

• Effects in pregnancy, breastfeeding or children: no study has included them.
• Whether maca changes how medicines work in people.
• What daily use beyond about eight months does.
• Whether colours, forms or amounts differ in side effects.
• How often rare effects occur: the largest trial had 175 people.

Frequently asked questions

Is 500 mg of maca too much?

It is below every amount the trials used, 0.6 g to about 5 g a day.^{1, 10} For an extract, check whether 500 mg is the extract weight or its root equivalent.

Do you need to cycle maca?

No trial has tested breaks or cycling; all gave maca daily.

Can maca cause bloating, constipation or weight gain?

Two of 80 men had stomach or bowel upsets; one man elsewhere left with starch intolerance.^{1, 2} No cited trial reported constipation or weight gain as a side effect; in the 80-man trial weight rose on maca and placebo alike.¹ Dried maca is about 59% carbohydrate; 3 g carries roughly 9 kcal.¹⁹

Can maca affect a testosterone blood test?

In one UK case report, a woman taking maca extract had a falsely high reading on one test method.⁶ Tell the GP or laboratory about supplements before a hormone test.

Sources

1. Shin D et al. World Journal of Men's Health 2023. Randomised trial, 80 men, 12 weeks; publicly funded; three authors list company affiliations. PubMed 36593713
2. Melnikovova I et al. Phytotherapy Research 2021. Randomised trial, 50 men, 16 weeks; university-funded; maca supplied by a Peruvian producer. PubMed 34585449
3. Dording CM et al. Evid Based Complement Alternat Med 2015. Randomised trial, 45 women, 12 weeks; publicly funded. PubMed 25954318
4. Gonzales-Arimborgo C et al. Pharmaceuticals 2016. Randomised trial, 175 adults, 12 weeks; publicly funded; one author runs a small nutraceutical company. PubMed 27548190
5. Johnson-Arbor K et al. J Med Toxicol 2018. Case report, 1 woman. PubMed 29313251
6. Srikugan L et al. BMJ Case Rep 2011. Case report, 1 woman. PubMed 22700073
7. Xiao A et al. Chin Med J 2017. Case report, 1 man. PubMed 29237937
8. Food Standards Agency. Novel foods authorisation guidance, 30 May 2018: EU status decisions before 2021 apply in GB; the EU catalogue lists maca as not novel. gov.uk
9. NHS. Herbal medicines and complementary therapies. Page last reviewed 1 May 2026. nhs.uk
10. Valentová K et al. Food Chem Toxicol 2008. Randomised trial, adults with metabolic syndrome, 90 days; size not in the abstract; funding not checked. PubMed 18054420
11. NHS. Medicines in pregnancy. Page last reviewed 5 September 2022 (review overdue). nhs.uk
12. LiverTox: Maca. NIH reference entry, revised 10 April 2019. PubMed 31643869
13. NHS. Jaundice. Page last reviewed 22 January 2024. nhs.uk
14. Gonzales GF et al. Andrologia 2002. Randomised trial, men aged 21 to 56, 12 weeks; size and funding not stated in the abstract. PubMed 12472620
15. Zenico T et al. Andrologia 2009. Randomised trial, 50 men, 12 weeks; funding not stated in the paper's abstract. PubMed 19260845
16. Melnikovova I et al. Evid Based Complement Alternat Med 2015. Randomised pilot, 20 men, 12 weeks; maca supplied by a Peruvian producer; no funding statement. PubMed 26421049
17. Brooks NA et al. Menopause 2008. Randomised crossover, 14 women, 6 weeks each; a US public research grant is listed. PubMed 18784609
18. Weng PW et al. Int J Med Sci 2025. Placebo-controlled matched-pair trial, 20 men, 12 weeks; publicly funded. PubMed 39781531
19. Gonzales GF. Evid Based Complement Alternat Med 2012. Narrative review. PubMed 21977053
20. Meissner HO et al. Int J Biomed Sci 2006. Randomised crossover, 34 women, 4 months; supplier-linked: the lead author's company co-funded the programme and a maca supplier supplied the powder. PubMed 23675006
21. Loretz C et al. Drug Metab Dispos 2020. Laboratory study, 29 herbal supplements. PubMed 32719085
22. Siwek M et al. Front Pharmacol 2023. Review of 1,816 adverse-event reports. PubMed 37829299
23. Stojanovska L et al. Climacteric 2015. Randomised crossover, 29 women, 6 weeks on each; funding not checked. PubMed 24931003
24. Meissner HO et al. Int J Biomed Sci 2005. Pilot, 20 women for 3 months and 8 for eight months of maca in a nine-month programme; supplier-linked: the lead author's company co-funded it and a maca supplier shared the batch costs. PubMed 23674952

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