A large-scale study has found no evidence supporting claims that acetaminophen, the painkiller and fever reducer widely used to treat pain and fever during pregnancy and known by the brand name Tylenol, increases the risk of autism spectrum disorder (ASD) or attention-deficit/hyperactivity disorder (ADHD) in children.
According to JAMA Internal Medicine, a journal of the American Medical Association, a research team led by Professor Eric Yuk-fai Wan of the University of Hong Kong and Professor Ian Chi-kei Wong of Aston University in the United Kingdom analyzed 708,020 mother-child pairs using electronic medical records from Hong Kong's public healthcare system. The study found no significant association between acetaminophen use during pregnancy and the risk of ASD and ADHD in children, the researchers said Sunday.
Acetaminophen is used as a first-line recommended medication for treating pain and fever during pregnancy. However, because it crosses the placenta, concerns have been raised that it could affect fetal neurodevelopment. Some observational studies have reported links to an increased risk of ASD or ADHD in children, fueling ongoing controversy.
In particular, U.S. President Donald Trump heightened the controversy at a press conference on September 22 last year, claiming that taking Tylenol during pregnancy could increase a child's risk of autism spectrum disorder. The remarks were criticized for lacking medical evidence and for creating unnecessary anxiety among pregnant women, autism patients and their families.
To exclude as much as possible the influence of genetic factors and home environment, the research team conducted a study comparing siblings who differed in whether they were exposed to acetaminophen during pregnancy. The ASD analysis included 124,333 individuals, and the ADHD analysis included 97,285 individuals.
The analysis showed that acetaminophen use during pregnancy did not increase the risk of autism spectrum disorder (adjusted hazard ratio 1.00) or attention-deficit/hyperactivity disorder (adjusted hazard ratio 1.01) in children.
The results did not change when the team separately analyzed the timing of use — early, middle and late pregnancy — as well as cases of use in only one period, use in two or more periods, and use throughout pregnancy. An analysis taking cumulative dosage into account also found no significant increase in risk.
The research team explained that while a general cohort analysis showed an association between Tylenol use and an increased risk of ASD and ADHD, similar results appeared even for pre-pregnancy use, which cannot affect the fetus. This suggests that confounding variables such as common factors within families, rather than the drug itself, may have had an effect, the team analyzed.
"In the sibling comparison study, we did not confirm an association between acetaminophen use during pregnancy and the risk of ASD or ADHD," the research team said. "The association raised in previous studies is more likely to have been influenced by common factors within families than by the drug."
The team added, "This study further strengthens the evidence that acetaminophen exposure during pregnancy is not a major risk factor for ASD and ADHD in children," and "it provides important evidence that using Tylenol during pregnancy is safe when medically necessary."
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