Many medications are off-limits during pregnancy.  A new study suggests that moms-to-be may want to add Tylenol to that list.
Many medications are off-limits during pregnancy. A new study suggests that moms-to-be may want to add Tylenol to that list.

Very little is known about the effects of medications during pregnancy. Due to the vulnerability of the population, most pregnant women are excluded from drug safety studies. Most over-the-counter medications, such as Tylenol, have been considered safe during pregnancy. In fact, Tylenol has been highly recommended by physicians as the pain reliever of choice for pregnant moms.

A new Norwegian study published in the journal Pediatrics has caused pause for some parents. The study found that long-term use of Tylenol, also known as acetaminophen or paracetamol, during pregnancy might increase the risk of developing attention deficit hyperactivity disorder, or ADHD.

Related: Taking Tylenol While Pregnant Linked to Childhood Asthma

The researchers analyzed data collected from the Norwegian Mother and Child Cohort Study, which included information on 75,217 fathers, 95,242 mothers, and 114,744 children born between 1999 and 2009.

Parents completed questionnaires about acetaminophen use at 18 weeks' gestation, and then again during pregnancy and after delivery. Maternal questionnaires were also collected when the child reached six months old, one and a half years old, and three years old. Information on the children's ADHD diagnoses were obtained from the Norwegian Patient Registry.

The final study population included 112,973 children, of whom 2246 had been diagnosed with ADHD. Approximately half of the women in the study used acetaminophen at some point during pregnancy.

"We found that using acetaminophen for 29 days or more during pregnancy gave a 220% increase in risk for ADHD in the child," said Eivind Ystrom, lead author. "This was after taking medical conditions and risk for ADHD in the family into account."

Related: Childhood Sleep Disturbances May Be Misdiagnosed as ADHD

However, Tylenol use by pregnant woman for less than seven days was associated with a decreased risk of ADHD in the children. Also impressive was the fact that while no association was found between the mother's acetaminophen use before pregnancy and the development of ADHD, paternal use was strongly associated with ADHD.

The researchers assert that the results of the study should not deter women from taking acetaminophen for an occasional headache or pain, but that long-term use should be discussed with a doctor.

This study is not the first of its kind to associate a link between acetaminophen and childhood behavioral problems. A 2016 study published in JAMA Pediatrics found that children exposed to acetaminophen during pregnancy are at risk of multiple behavioral difficulties.