A Danish study of about 64,000 mothers and children found an association between acetaminophen use during pregnancy and a higher likelihood of attention deficit hyperactivity disorder (ADHD) or related behavioral problems in children. Acetaminophen, also known as paracetamol and sold in products including Tylenol, is commonly recommended for mild pain and fever during pregnancy.

Published in *JAMA Pediatrics*, the study used data from the Danish National Birth Cohort, collected between 1996 and 2002. About half of the mothers reported taking acetaminophen while pregnant. Researchers examined reports of children’s behavior alongside records of ADHD diagnoses and prescriptions. Acetaminophen use was associated with a 29% higher risk of an ADHD diagnosis and a 37% higher risk of the more severe and rarer diagnosis of hyperkinetic disorder. Longer use, particularly later in pregnancy, was associated with higher risks; children whose mothers reported use for 20 weeks had a 50% higher risk of receiving ADHD medication. The study measured weeks of use, not dosage.

The findings **do not establish that acetaminophen causes ADHD**. Infections, fever, genetic factors or other differences among women who used the drug could also help explain the association. ADHD has multiple genetic and environmental risk factors, and ADHD-like behaviors are not the same as a diagnosis. Researchers have suggested that acetaminophen might affect hormones involved in fetal brain development, but that proposed explanation remains uncertain.

Study author Dr. Beate Ritz advised avoiding chronic or long-term use while more research is conducted, while emphasizing that a single dose does not mean a child will develop hyperactivity. Other experts cautioned that one study is insufficient to recommend that pregnant women never use acetaminophen. They suggested weighing the benefits and risks of treatment and considering non-drug approaches to pain, such as massage, baths or acupuncture.

Tylenol maker McNeil Consumer Healthcare said that acetaminophen has a favorable safety profile when used as directed and that no prospective randomized controlled studies have established a causal link to adverse child development. It recommends that pregnant and breastfeeding women consult their doctors before taking medication.