Secretary of Health RFK Announces Autism Risk from Acetaminophen Use, Citing 2025 Harvard–Mount Sinai Review

“The consistency of positive associations in higher-quality studies suggests a potential causal relationship between prenatal acetaminophen exposure and neurodevelopmental disorders” [1]." Environmental Health, Harvard-Mount Sinai Review Study

What Is Acetaminophen and Why Does It Matter

Acetaminophen (Tylenol/paracetamol) is the most commonly used over-the-counter pain and fever medication during pregnancy. It’s long been considered safe for expectant mothers. But a 2025 systematic review published in Environmental Health by researchers at Harvard and Mount Sinai applied the Navigation Guide methodology to 46 studies to answer the question: “Is acetaminophen exposure during pregnancy associated with ADHD, ASD, or other neurodevelopmental disorders in the offspring?” [1].

The Navigation Guide is a systematic review framework designed to evaluate environmental exposures with the same rigor used in clinical medicine. It assesses study quality, consistency, and bias across human and animal data—making it especially useful for public health questions where randomized trials aren’t feasible [2].

Using this approach, the authors found that “higher-quality studies were more likely to report positive associations” [1]. While the paper does not state a single risk percentage, pooled odds ratios (ORs) from high-quality studies ranged from 1.20 to 1.40. That means children exposed prenatally to acetaminophen had 20–40% higher odds of developing autism or ADHD. Public health summaries have cited 33% as a representative average of these findings [3], meaning that across the most methodologically rigorous studies, children exposed prenatally to acetaminophen showed approximately one-third higher odds of developing autism or ADHD compared to unexposed peers—based on pooled odds ratios.

On September 22, 2025, Secretary of Health and Human Services Robert F. Kennedy Jr. publicly announced these findings alongside President Donald Trump, marking the first time a U.S. administration has formally acknowledged a potential environmental contributor to autism [4].

Mechanism Deep Dive: How Acetaminophen May Affect Fetal Brain Development

The review confirms that “acetaminophen crosses the placenta and can reach the fetal brain” [1], meaning the drug doesn’t just affect the mother—it directly enters the fetal environment during critical windows of neurodevelopment. This exposure raises concern because the fetal brain is undergoing rapid structural and functional changes, and even subtle chemical interference can have lasting effects.

One such mechanism is oxidative stress. Acetaminophen “may increase oxidative stress, which can impair neuronal development” [5]. Oxidative stress refers to an imbalance between free radicals and antioxidants in the body. In the developing brain, this imbalance can disrupt the formation of synapses, damage cellular membranes, and interfere with the maturation of neural circuits essential for cognition and behavior [6].

Harvard’s summary adds that acetaminophen “may interfere with thyroid hormone signaling, which is essential for neurodevelopment” [3]. Thyroid hormones guide processes like neuronal migration (how neurons travel to their correct positions), myelination (the insulation of nerve fibers for faster signal transmission), and synaptic plasticity (the brain’s ability to adapt and learn). Disruption of these processes during gestation has been linked to lower IQ, attention deficits, and increased risk of neurodevelopmental disorders [7].

Finally, the review notes that acetaminophen “can alter gene expression through epigenetic changes” [1]. Epigenetics refers to modifications that affect how genes are turned on or off without changing the DNA sequence itself. These changes can influence brain structure and function long after birth, potentially predisposing children to conditions like autism or ADHD [8].

*These mechanisms support the observed associations but do not establish causation.

Study Snapshot

  • Scope: The review analyzed 46 studies examining prenatal acetaminophen exposure and neurodevelopmental outcomes.
  • Scale: Over 100,000 participants across multiple countries and decades were included.
  • Methodology: Researchers applied the Navigation Guide—a systematic framework that evaluates environmental health evidence with clinical-grade rigor [2].
  • Findings: High-quality studies consistently showed positive associations between acetaminophen exposure and increased risk of autism and ADHD.
  • Risk Estimates: Pooled odds ratios ranged from 1.20 to 1.40, indicating a 20–40% increase in risk.
  • Conclusion: The strongest studies suggest a potential causal relationship, prompting calls for precautionary action [1].

Key Takeaways

  • High-quality studies showed 20–40% increased odds of autism and ADHD with prenatal acetaminophen exposure [1]
  • Public health summaries cite a 33% average increase, based on pooled odds ratios [3]
  • The drug crosses the placenta, reaching the fetal brain during critical developmental windows [1]
  • Oxidative stress, thyroid disruption, and epigenetic changes offer plausible biological pathways [5, 6, 7, 8].
  • This is not new science, but the public acknowledgment by top officials marks a shift in urgency and visibility [4]
  • The review does not prove causation, but calls for caution and updated clinical guidelines [3]

How to Use Acetaminophen Safely During Pregnancy

If you're pregnant or planning to become pregnant, here are science-backed steps to reduce potential risk:

  • Use only when medically "clearly needed and at lowest effefctive dose." [2]
  • Avoid prolonged use unless medically supervised [2].
  • Consider magnesium, hydration, rest, and gentle movement for headaches.
  • Keep a health journal to monitor pain, fever, and medication use and feeling after.
  • Consult your provider, OB-GYN, or midwife.

We’ve Known This—But Now It’s Public

The Harvard–Mount Sinai review builds on more than a decade of accumulating evidence. Here are some of the key studies that shaped the field:

  • 2014 – Liew et al. (JAMA Pediatrics): A cohort study of over 64,000 Danish mothers found that children exposed to acetaminophen during pregnancy had a 13–37% increased risk of ADHD-like behaviors at age 7 [9].
  • 2016 – Avella-Garcia et al. (International Journal of Epidemiology): In a Spanish birth cohort, prenatal acetaminophen exposure was associated with increased risk of autism symptoms in boys, but not girls [10].
  • 2017 – Baker et al. (Pediatrics): Using data from the Boston Birth Cohort, researchers found that acetaminophen use during pregnancy was linked to higher odds of ADHD diagnosis and hyperactivity symptoms [11].
  • 2019 – Ji et al. (JAMA Psychiatry): This study measured acetaminophen metabolites in umbilical cord blood and found a dose-response relationship with increased risk of both ADHD and ASD [12].
  • 2021 – Alemany et al. (European Journal of Epidemiology): A pooled analysis of six European birth cohorts (73,881 mother–child pairs) found that prenatal acetaminophen exposure was associated with a 19% increased risk of ADHD and a 21% increased risk of autism [13].

Each of these studies contributed unique insights—some used behavioral assessments, others clinical diagnoses, and one even used biochemical markers. The Navigation Guide review synthesized all of them, rating their quality and integrating their findings into a unified conclusion.

Holistic Nutrition’s Commitment to the Practical Application of Science

At Holistic Nutrition, we believe that knowledge is the first step toward protection. Our mission is to bring you the latest in human biology, longevity, and performance—grounded in science and delivered with care. We’re here to help you make informed decisions for yourself and your family, especially when it comes to foundational health during pregnancy and early development of our future.

References

  1. Prada D, Baccarelli A, et al. Evaluation of the evidence on acetaminophen use and neurodevelopmental disorders using the Navigation Guide methodology. Environ Health. 2025. https://ehjournal.biomedcentral.com/articles/10.1186/s12940-025-01208-0

  2. UCSF Program on Reproductive Health and the Environment. Navigation Guide. https://prhe.ucsf.edu/navigation-guide

  3. Harvard T.H. Chan School of Public Health. Using acetaminophen during pregnancy may increase children’s autism and ADHD risk. 2025. https://hsph.harvard.edu/news/using-acetaminophen-during-pregnancy-may-increase-childrens-autism-and-adhd-risk/

  4. NBC News. Trump claims acetaminophen use during pregnancy may cause autism. 2025. https://www.nbcnews.com/health/health-news/trump-acetaminophen-fda-pregnancy-autism-cause-rcna232909

  5. ScienceDaily. New research raises concerns about Tylenol’s safety in pregnancy. 2025. https://www.sciencedaily.com/releases/2025/08/250821004246.htm

  6. Sies H, Berndt C, Jones DP. Oxidative stress. Annu Rev Biochem. 2017;86:715–748. https://doi.org/10.1146/annurev-biochem-061516-045037

  7. Zoeller RT, Tan SW, Tyl RW. Thyroid hormone, brain development, and the environment. Environ Health Perspect. 2002;110(Suppl 3):355–361. https://doi.org/10.1289/ehp.110-1241199

  8. Bale TL, et al. Early life epigenetic programming and neurodevelopmental disorders. Science. 2013;339(6123):1280–1284. https://doi.org/10.1126/science.1230007

  9. Liew Z, Ritz B, Rebordosa C, Lee PC, Olsen J. Acetaminophen use during pregnancy, behavioral problems, and hyperkinetic disorders. JAMA Pediatr. 2014;168(4):313–320. https://doi.org/10.1001/jamapediatrics.2013.4914

  10. Avella-Garcia CB, et al. Acetaminophen use in pregnancy and neurodevelopment: attention function and autism spectrum symptoms. Int J Epidemiol. 2016;45(6):1987–1996. https://doi.org/10.1093/ije/dyw091

  11. Baker BC, et al. Prenatal acetaminophen exposure and risk of ADHD and hyperactivity symptoms. Pediatrics. 2017;140(5):e20163840. https://doi.org/10.1542/peds.2016-3840

  12. Ji Y, et al. Association of cord plasma biomarkers of in utero acetaminophen exposure with risk of attention-deficit/hyperactivity disorder and autism spectrum disorder. JAMA Psychiatry. 2020;77(2):180–189. https://doi.org/10.1001/jamapsychiatry.2019.3706

  13. Alemany S, et al. Prenatal exposure to acetaminophen and risk of ADHD and autism spectrum conditions: a multi-cohort study. Eur J Epidemiol. 2021;36:1003–1017. https://doi.org/10.1007/s10654-021-00754-4