What is the link between acetaminophen (Tylenol) use and autism spectrum disorder (ASD)?

Acetaminophen Use and Autism Spectrum Disorder: Current Evidence

Studies linking acetaminophen (Tylenol) use during pregnancy to autism spectrum disorder (ASD) show an association but not definitive causation, with the strongest evidence indicating a possible link specifically to ASD with hyperkinetic symptoms rather than ASD broadly. 1

Evidence Overview

The relationship between prenatal acetaminophen exposure and neurodevelopmental outcomes has been studied with increasing interest in recent years. According to the Society for Maternal-Fetal Medicine (SMFM) and the American College of Obstetricians and Gynecologists (ACOG), the current evidence shows:

• Prenatal acetaminophen exposure has been associated with increased risk of ASD, with a hazard ratio of 1.51 (95% CI 1.19-1.92) specifically for ASD with hyperkinetic disorder 1
• Maternal prenatal acetaminophen use shows a risk ratio of 1.19 (95% CI, 1.14,1.25) for ASD outcomes generally 1
• Longer duration of use (>20 weeks in gestation) may increase the risk of ASD with hyperkinetic symptoms almost twofold (RR = 1.63) 1, 2

Key Studies and Their Findings

Danish National Birth Cohort Study (2016)

This large prospective cohort study followed 64,322 children for an average of 12.7 years and found:

• Prenatal acetaminophen use was associated with increased risk of ASD with hyperkinetic symptoms (HR = 1.51,95% CI 1.19-1.92)
• No significant association was found with other ASD cases without hyperkinetic symptoms (HR = 1.06,95% CI 0.92-1.24)
• Longer duration of use (>20 weeks) nearly doubled the risk of ASD with hyperkinetic symptoms 2

Recent Comprehensive Review (2025)

A systematic review using the Navigation Guide methodology examined 46 studies and found:

• The majority of studies reported positive associations between prenatal acetaminophen use and neurodevelopmental disorders including ASD
• Higher-quality studies were more likely to show positive associations
• The evidence was deemed consistent with an association between acetaminophen exposure during pregnancy and increased incidence of neurodevelopmental disorders 3

Important Nuances in the Research

Several important caveats should be considered when interpreting these studies:

• The association appears strongest for ASD with hyperkinetic features, suggesting the predisposition may be toward hyperkinetic syndrome rather than autism broadly 1, 4
• Dose and duration matter: longer exposure (>28 consecutive days) shows stronger associations 1
• Third trimester exposure shows the highest risk for ADHD outcomes 1
• Despite these associations, the weight of evidence is still considered inconclusive regarding a definitive causal relationship 1

Clinical Implications

Based on the current evidence, healthcare providers should:

• Discuss risks versus benefits with patients considering acetaminophen use during pregnancy
• Advise using the lowest effective dose for the shortest possible time when acetaminophen is needed
• Consider non-pharmacological approaches for mild to moderate pain when appropriate
• Not withhold acetaminophen when clearly indicated, as fever and pain during pregnancy carry their own risks 1, 5

Research Limitations

The current body of research has several limitations:

• Most studies are observational rather than randomized controlled trials
• Recall bias may affect self-reported medication use
• Confounding factors such as the underlying conditions requiring acetaminophen use may influence outcomes
• Different studies use varying definitions and assessments of neurodevelopmental outcomes

While some researchers have made strong claims about acetaminophen causing autism 6, the consensus from medical societies is that the evidence remains inconclusive regarding causation, though the associations warrant continued research and cautious use during pregnancy.