Quick answer
NIH's finding of no safety concerns for BCAAs at 20 g a day or less for up to 6 weeks does not cover pregnancy. A 2020 systematic review found that BCAA supplements did not change fetal or birth weight, and a mouse study found abnormal fetal and placental growth. Ask your doctor before taking BCAAs while pregnant.1,2,3
Key facts
- NIH reports no safety concerns for BCAA supplements at 20 g a day or less for up to 6 weeks. It describes no study in pregnant women.1
- A 2020 systematic review of 22 human and 89 animal studies of amino acids in pregnancy found that BCAA supplementation did not affect fetal or birth weight.2
- In pregnant mice, isoleucine in drinking water on days 2 to 10 changed fetal and placental growth, with pups 9% larger than normal at day 19 but smaller at day 20.3
- A 2022 safety review lists pregnancy among the circumstances that need more research before amino acid supplements can be judged suitable.4
- NIH advises caution with supplements beyond a standard prenatal supplement in pregnancy, because many have not been well tested in pregnant women.5
What a 2020 systematic review found
The main systematic evidence is a review that combined 22 human and 89 animal studies in which pregnant women or animals took amino acids by mouth. It sorted them into three groups, the arginine family, the branched-chain amino acids and methyl donors, and its main outcome was fetal or birth weight.2
For the branched-chain group the review found no effect on fetal or birth weight, and its authors said BCAA supplements do not seem as promising as arginine for targeting fetal growth. Birth weight is only one outcome, and the review's abstract does not say how many of the studies tested BCAAs or whether they were in women. It also calls for well-controlled research in complicated pregnancies.2
What an animal study found
A 2020 study gave pregnant mice isoleucine, one of the three BCAAs, in their drinking water on days 2 to 10 of pregnancy. On day 19, the pups were 9% larger than normal, while on day 20 they were smaller. The normal link between birth weight and litter size was lost, and fetal and placental weights stopped tracking each other as they normally do.3
The authors said other unintended effects of BCAA use should be studied because athletes use BCAAs more and more. A mouse study cannot say what happens in women, and it used a single amino acid at a concentration that the paper does not tie to supplement amounts, so it is a reason for further research, not a finding of harm in people.3
What NIH says
NIH's health professional sheet reports no safety concerns for BCAA supplements at 20 g a day or less for up to 6 weeks, and lists no known adverse effects. It does not name a study in pregnant women, and NIH's consumer sheet says much of the research on performance supplements is done in young healthy men. NIH also says a diet with enough protein can easily provide 10 to 20 g of BCAAs a day.1,6
NIH lists no known side effects and no safety concerns at 20 g a day or less for up to 6 weeks.1
Large amounts of BCAAs raise the body's production of ammonia. A review of amino acid supplements says they may be harmful for people with liver disease and appear inappropriate for people with diabetes.4
The 2022 review of amino acid supplement side effects adds that pregnancy and nursing are circumstances in which more study is needed.4
Who should ask their doctor
Ask your doctor or midwife before taking BCAAs, or a drink or powder that contains them, while pregnant or planning a pregnancy. NIH advises caution with supplements beyond a standard prenatal supplement, and it notes that most ingredient combinations in performance supplements have not been studied. Ask especially if you have liver disease, diabetes or a metabolic condition.4,5,6
Questions people ask
Can you take BCAA while pregnant?
The sources checked report no trial of BCAA supplements in pregnant women. A 2020 systematic review found no change in fetal or birth weight, and NIH's safety finding does not describe pregnancy. Ask your doctor.1,2
Can you drink BCAA while pregnant?
The sources checked do not address BCAA drinks. NIH notes that performance supplements can contain many ingredients in different combinations that have mostly not been studied, so bring the label to your doctor.6
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Sources
- National Institutes of Health, Office of Dietary Supplements. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. Updated April 1, 2024. Opened 2026-10-07.
- Terstappen F, Tol AJC, Gremmels H, et al. Prenatal amino acid supplementation to improve fetal growth: a systematic review and meta-analysis. Nutrients. 2020;12(9):2535. Opened 2026-10-11.
- To CY, Freeman M, Van Winkle LJ. Consumption of a branched-chain amino acid (BCAA) during days 2-10 of pregnancy causes abnormal fetal and placental growth: implications for BCAA supplementation in humans. Int J Environ Res Public Health. 2020;17(7):2445. Mouse study. Opened 2026-10-11.
- Holeček M. Side effects of amino acid supplements. Physiol Res. 2022;71(1):29-45. Opened 2026-10-01.
- National Institutes of Health, Office of Dietary Supplements. Dietary Supplements: What You Need To Know. Fact sheet for consumers. Updated January 4, 2023. Opened 2026-10-07.
- National Institutes of Health, Office of Dietary Supplements. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Consumers. Updated March 22, 2021. Opened 2026-10-07.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.