A Danish study of more than 64,000 mothers and children found an association between acetaminophen use during pregnancy and later ADHD-related diagnoses and behaviors in children. Acetaminophen, also known as paracetamol and sold under the brand name Tylenol, is commonly recommended during pregnancy to relieve pain and fever.

Researchers analyzed data from the Danish National Birth Cohort, whose participants were enrolled between 1996 and 2002. Mothers reported medication use during pregnancy and their children’s behavior, while 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.

Women who reported any acetaminophen use had a 29% higher risk of having a child diagnosed with ADHD and a 37% higher risk of a hyperkinetic disorder diagnosis. Longer use and use later in pregnancy were associated with greater risks. Children whose mothers reported taking acetaminophen 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 measured in the study are not the same as an ADHD diagnosis.

The researchers and other experts stressed that the findings **do not establish that acetaminophen causes ADHD**. Other factors could explain the association, including infections or pain experienced during pregnancy, genetic predisposition, and possible acetaminophen use by children after birth. ADHD is complex and has multiple genetic and environmental risk factors. Researchers proposed that acetaminophen might affect hormones involved in fetal brain development, but experts questioned whether the cited evidence established that mechanism in humans.

Study author Dr. Beate Ritz said pregnant women should not be alarmed by occasional use, but suggested avoiding frequent or long-term use until more is known. Other doctors emphasized weighing the benefits and risks of treatment and considering non-drug options for pain, such as massage, baths or acupuncture. Tylenol maker McNeil Consumer Healthcare advised pregnant and breastfeeding women to consult their doctors before taking medication and noted that no prospective randomized controlled studies had demonstrated a causal link to adverse child-development effects.