A Danish study has found an association between acetaminophen use during pregnancy and a higher risk of attention deficit hyperactivity disorder (ADHD) diagnoses and related behavioral problems in children. The findings raise questions about a drug commonly recommended to pregnant women for mild pain and fever, but they do not establish that it causes ADHD.

Published in *JAMA Pediatrics*, the study analyzed data on approximately 64,000 children and their mothers in the Danish National Birth Cohort. About half the mothers reported taking acetaminophen, also known as paracetamol and sold under the Tylenol brand, during pregnancy. Researchers examined mothers’ reports of their children’s behavior alongside records of ADHD diagnoses and prescriptions.

Children whose mothers reported taking acetaminophen had a 29% higher risk of an ADHD diagnosis and a 37% higher risk of the rarer, more severe hyperkinetic disorder. Longer use and use later in pregnancy were associated with higher risks; children of women who reported taking the drug for 20 weeks had a 50% higher risk of being prescribed ADHD medication. The study measured the number of weeks of reported use, however, rather than the dose taken. ADHD-like behaviors are also not the same as an ADHD diagnosis.

Researchers suggested that acetaminophen might affect hormones involved in fetal brain development, but other explanations remain possible. An infection or other condition that led a woman to take the drug could influence development, as could genetic factors associated with both pain sensitivity and ADHD. Experts noted that ADHD is complex and involves both genetic and environmental factors.

Study author Dr. Beate Ritz advised against frequent or long-term use while more research is conducted, rather than suggesting that a single dose will cause harm. Other physicians cautioned that one observational study is not enough to rule out acetaminophen during pregnancy. They suggested considering non-drug approaches to pain, such as massage, baths or acupuncture, and weighing the benefits and risks of treatment for each condition. The study could not meaningfully compare acetaminophen with other painkillers because few participants used them.

Tylenol maker McNeil Consumer Healthcare said pregnant and breastfeeding women should consult their doctors before taking medication. It also stated that no prospective randomized controlled studies have established a causal link between acetaminophen use in pregnancy and adverse effects on child development.