Topline
A new study which compared siblings who were and weren’t exposed to acetaminophen during pregnancy found the drug doesn’t increase the risk of autism and ADHD, adding new evidence to a long-debated topic.
A pregnant mother holding her belly.
Key Facts
The researchers followed millions of children for 26 years after they were born, and they did see a small increase in ADHD, autism and intellectual disability in the overall population compared to when they were younger; around 7.5% were exposed to acetaminophen (the active ingredient in Tylenol) during pregnancy.
The risk of developing these neurodevelopmental disorders in kids who weren’t exposed to acetaminophen before birth versus those who were was 1.33% vs 1.53% for autism, 2.46% vs 2.87% for ADHD, and 0.70% vs 0.82% for intellectual disability, according to the study published Tuesday in JAMA Network Open.
However, the researchers decided to also use a sibling model to examine the risks, because prenatal acetaminophen exposure was more common in kids with parents who smoked during pregnancy, had lower socioeconomic status and previous diagnoses of neurodevelopmental disorders, all potential risk factors for ADHD and autism.
They didn’t find any increased risk when comparing siblings who were exposed to acetaminophen before birth and those who weren't exposed, meaning the increased risk of developing neurodevelopmental disorders may be due to other factors like genetics.
Some previous research has concluded prenatal acetaminophen use may increase the risk of neurobehavioral issues, but the current study found no evidence to support a cause-and-effect link when using a sibling model.
The study researchers noted that because siblings share a large portion of the same genetic background and may be exposed to similar environmental factors during pregnancy, comparing siblings—which most previous studies didn’t do—helps to control for these outside factors.
Acetaminophen is the only pain reliever generally considered safe for use during pregnancy, but many pregnant people may not take acetaminophen due to fears of potentially harmful side effects, so the researchers are hopeful this study provides “reassurance” to expectant parents.
Crucial Quote
“This study’s findings may be welcome news for birthing people who use acetaminophen as a pain or fever management option, since there are few safe alternatives for relief available,” Renee Gardner, a study author and principal researcher at Sweden’s Karolinska Institutet, said in a statement.
Big Number
2.4 million. That’s how many children—who were all born in Sweden—were used as a part of this cohort, making this the largest study to date to examine the connection between Tylenol and ADHD, autism and intellectual disability, according to the study.
Contra
Acetaminophen’s link to neurodevelopmental disorders has been a controversial topic within the health community, as several studies have previously found the drug does cause an increase in neurobehavioral issues. Children whose umbilical cord blood samples had the highest doses of acetaminophen were around three times more likely to develop ADHD and autism, according to a separate JAMA study published in 2019. An international group of researchers recommended in 2021 that pregnant individuals limit their exposure by using the lowest effective dose for the shortest amount of time, and called for more warnings around taking acetaminophen during pregnancy, according to research published in Nature Reviews Endocrinology. However, they noted other factors like maternal alcohol use and stress may also play a role. Long term acetaminophen use during pregnancy resulted in a 20% higher risk of autism and a 30% higher risk of ADHD, a 2018 meta analysis published in the American Journal of Endocrinology found.
Key Background
A separate 2021 study also used a sibling model to examine this link, and it found both the exposed and unexposed children of mothers who took acetaminophen during pregnancy had an increased risk of developing ADHD. The researchers concluded these results may be partly due to “unobserved familial factors.” The Food and Drug Administration said in 2015 evidence was too “limited” to make any recommendations against using over-the-counter medications like acetaminophen during pregnancy. A class action lawsuit was brought against the makers of Tylenol and similar generic versions of the drug partially due to the recommendations from the 2021 Nature paper. However, a federal judge ruled in December 2023 the research cited in the lawsuit cannot be used as evidence since at least one of experts the plaintiffs used "cherry-picked and misrepresented study results and refused to acknowledge the role of genetics in the etiology of either [autism spectrum disorder] or ADHD." In September 2023, the FDA declined to comment on the lawsuit, though it conducted a new review of more recent studies earlier that year and said they were “limited” and “inconsistent.” Other medical bodies like the American College of Obstetricians and Gynecologists (ACOG) maintain that acetaminophen use during pregnancy is safe in moderation.
Further Reading
Federal judge says research can't be used to link acetaminophen to autism, ADHD (ABC News)
