A Danish study of more than 64,000 mothers and children found an association between acetaminophen use during pregnancy and a higher likelihood of ADHD-related diagnoses and behaviors in children. Acetaminophen, also known as paracetamol and sold as Tylenol, is commonly recommended during pregnancy to relieve pain and fever. The findings, published in *JAMA Pediatrics*, do not establish that the drug causes ADHD.

Researchers analyzed data from the Danish National Birth Cohort, which enrolled children between 1996 and 2002. Mothers reported their medication use during pregnancy and their children’s behavior; researchers also examined records of ADHD medication prescriptions and diagnoses of hyperkinetic disorder, a severe form of ADHD. More than half of the mothers reported taking acetaminophen at some point during pregnancy.

Compared with children whose mothers reported no use, those whose mothers had ever taken acetaminophen had a 29% higher risk of an ADHD diagnosis and a 37% higher risk of a hyperkinetic disorder diagnosis. Longer use and use later in pregnancy were associated with higher risks. Children of women who reported taking the drug for at least 20 weeks had a 50% higher risk of receiving ADHD medication. The study measured the number of weeks of use but did not account for dosage. ADHD-like behaviors are also distinct from an ADHD diagnosis.

Researchers considered whether fever or flu symptoms might explain the association, but other factors remain possible. Unrecognized infections, genetic predisposition or acetaminophen given to children after birth could play a role. The study authors suggested that acetaminophen might interfere with hormones important to fetal brain development, though other experts questioned the relevance of the evidence cited for that theory. ADHD has multiple genetic and environmental risk factors.

Study author Dr. Beate Ritz said pregnant women should not panic, but suggested avoiding frequent or prolonged painkiller use until more is known. Other experts emphasized weighing the benefits of treatment against potential risks and considering pain relief measures such as baths, massage or acupuncture. Tylenol maker McNeil Consumer Healthcare advised pregnant and breastfeeding women to consult their doctors before taking medication and said randomized controlled studies have not demonstrated a causal link between prenatal acetaminophen use and adverse child development.