Research shows no causal link between Tylenol and autism

A new study from JAMA found that using acetaminophen, the active ingredient in Tylenol, during pregnancy was not associated with increased risk of autism, ADHD or intellectual disability in children. The study refuted recent research papers and statements that suggest that acetaminophen use during pregnancy increases risk of ADHD and other neurodevelopmental disorders.

The study, funded by National Institutes of Health (NIH) and conducted by Karolinska Institute in Sweden and Drexel University, is the largest of its kind. Researchers analyzed data from almost 2.5 million Swedish children born between 1995 and 2019.

The results showed that while researchers initially found that children who were exposed to acetaminophen were slightly more likely to have autism, ADHD and intellectual disabilities versus those who were not, this risk disappeared when comparing pairs of siblings. Because siblings share genetics and typically grow up in similar environments, sibling studies are thought to be more accurate and have a smaller risk of external factors skewing the results.

This study’s findings suggest that in previous analyses, there were likely other variables that distorted the results. For example, the current study found that parents who have neurodevelopmental disorders are more likely to use acetaminophen during pregnancy. Children of these parents are also more likely to a neurodevelopmental disorder; however, this is not necessarily due to their exposure to acetaminophen, but rather due to the high heritability of these disorders.

Acetaminophen exposure was also more common among children born to parents in a lower socioeconomic class, with a higher early pregnancy body mass index, those who smoked during pregnancy and those with psychiatric disorders.

One limitation of this study is that it relies on prescription data and self-reporting, which means it may not have captured all over-the-counter acetaminophen usage. However, with this large of a sample size and ability to control for external variables, the conclusions of this study are more robust and well-supported by evidence.