A Danish study has found an association between acetaminophen use during pregnancy and a higher likelihood of ADHD-related diagnoses and behaviors in children. Researchers and outside experts cautioned that the findings do not establish that the drug causes ADHD and said more research is needed.

Published in *JAMA Pediatrics*, the study analyzed data on more than 64,000 children and their mothers enrolled in the Danish National Birth Cohort between 1996 and 2002. Mothers reported medication use during pregnancy and later described their children’s behavior. Researchers also examined records of ADHD medication prescriptions and diagnoses of hyperkinetic disorder, a severe form of ADHD. About half of the mothers reported taking acetaminophen, also known as paracetamol and sold under the brand name Tylenol.

Women who reported taking acetaminophen at any point during pregnancy had a 29% higher risk of having a child diagnosed with ADHD and a 37% higher risk of a hyperkinetic syndrome diagnosis. Longer use and use later in pregnancy were associated with higher risks. Children whose mothers reported taking the drug for 20 weeks or more had a 50% higher risk of receiving ADHD medication. The study measured the number of weeks of use but did not establish a dose-based risk. ADHD-like behaviors are also distinct from an ADHD diagnosis.

The researchers considered whether fever or illness might explain the association, but other factors remain possible. Some infections may have gone unrecognized, and genetic or family characteristics could affect both painkiller use and ADHD risk. The authors suggested that acetaminophen might interfere with hormones involved in fetal brain development, although an outside neurologist questioned the relevance of the cited evidence to humans. ADHD has multiple genetic and environmental risk factors.

Study author Dr. Beate Ritz said occasional use should not be a cause for alarm, but advised pregnant women to avoid frequent or long-term use when possible until more is known. Other experts stressed weighing the benefits and risks of treatment and suggested non-drug approaches to pain, such as massage, baths or acupuncture. Tylenol maker McNeil Consumer Healthcare said pregnant and breastfeeding women should consult their doctors before taking medication and noted that randomized studies have not demonstrated a causal link to adverse child development.