A recent article posted on the online journal JAMA Pediatrics suggests that acetaminophen (Tylenol, Paracetamol), an over-the-counter pain reliever widely used during pregnancy, may have a harmful effect on fetal brain development, increasing the risk of conditions such as attention-deficit/hyperactivity disorder (ADHD) and other hyperkinetic disorders (HKD) in children. Pregnant women have long been counseled to avoid use of aspirin or other non-steroidal anti-inflammatories, such as ibuprofen (Advil, Motrin) during pregnancy, because of different concerns; instead to use only acetaminophen, considered “safe” for use during pregnancy. In fact, over half of all pregnant women in the study used acetaminophen while pregnant for common complaints such as headache, muscular aches and pains, and fever.

The study took place in Denmark. The authors studied 64,322 live-born children and mothers enrolled in the Danish National Birth Cohort during 1996-2002. The objective was to see if prenatal use of acetaminophen increased the risk for development of ADHD and other hyperkinetic disorders in offspring. Acetaminophen use during pregnancy was assessed with 3 computer-assisted telephone interviews during pregnancy and 6 months after child birth. Children were assessed with several tools, including parent’s reports of behavioral problems at age 7; diagnoses of HKD disorders recorded in the Danish hospital and psychiatric registries; and prescription of ritalin and similar drugs used to treat these conditions to children in the pharmacy registry.

The researchers found that children of mothers who used acetaminophen during pregnancy were up to 30 % more likely to be diagnosed with ADHD and 37% more likely to receive a diagnosis of HKD; more likely to have been prescribed ritalin or similar drugs for this condition, and/or more likely to exhibit HKD behaviors at age 7. If acetaminophen was used in more than one trimester of pregnancy, or if it was used more frequently by a mother, the risk of these outcomes was higher.

Critiques of this study mostly focus on likely confounders (other factors that could have been responsible). Behavior and attention problems are likely to have multiple causes, both genetic and environmental. For these reasons, the authors say that it’s too early to make any specific recommendations for pregnant women just yet. However, they also say that their results did not appear to be confounded by maternal inflammation, infection during pregnancy, mother’s mental health problems, or other potential factors that they evaluated. The authors conclude that, “because the exposure and outcome are frequent, these results are of public health relevance but further investigations are needed.” In other words, you may want to ask your midwife or doctor if you should be using acetaminophen (and how much), but don’t toss the container into the trash bin just yet. It is possible that the association between acetaminophen and HKD is just that (they just happen to occur in the same mother-baby couples), and that the real culprit in these disorders is something else entirely.

Liew Z, Ritz B, Rebordosa C, Lee PC, Olsen J. Acetaminophen Use During Pregnancy, Behavioral Problems, and Hyperkinetic Disorders JAMA Pediatr. Published online February 24, 2014. http://archpedi.jamanetwork.com/article.aspx?articleid=1833486