Study Finds Autism, ADHD Risks Linked to Prenatal Acetaminophen Use

Side effects of acetaminophen may alter an unborn child’s neurotransmission system, new research suggests.

Researchers are now warning that doctors should immediately begin advising women to limit their acetaminophen use during pregnancy, due to an increased risk of their children developing autism spectrum disorder (ASD) or attention deficit hyperactivity disorder (ADHD).

More than 50% of pregnant women report using Tylenol or another acetaminophen-based pain medication at some point during their pregnancy. However, findings published this month in the medical journal Environmental Health suggest that this could be increasing the risk of neurodevelopmental disorders (NDDs) among their offspring.

Tylenol Health Concerns

While most commonly known by its brand-name Tylenol, acetaminophen is a fever reducer and pain relief medication found in more than 600 different medications, according to the U.S. Food and Drug Administration (FDA).

For decades it has been believed to be safe and carry few serious side effects, but concerns have emerged in recent years about several potential health concerns linked to the medication.

Johnson & Johnson has faced hundreds of Tylenol autism and ADHD lawsuits filed by families who say the manufacturer failed to provide adequate warnings to pregnant women about the potential side effects on their children. However, most of that litigation ended when a federal judge dismissed plaintiffs’ expert witnesses in a controversial ruling last year, leaving families with no way to prove causation.

In recent years, there have also been widespread concerns about the risks of acetaminophen overdose, which has been identified as a leading cause for liver injury in the United States. Previous studies have indicated that it causes an estimated 50,000 emergency room visits each year, including 25,000 hospitalizations and more than 450 deaths.

Acetaminophen has also been linked to dangerous skin reactions, like Stephens-Johnson Syndrome (SJS), which can cause the skin to separate from the body and result in fatal complications. In 2014, the FDA issued a draft guidance calling for new label warnings for Tylenol and other acetaminophen drugs due to the risks of SJS, which is often referred to as toxic epidermal necrosis (TEN) when lesions cover large portions of the body. Last year, the FDA proposed making the label warnings mandatory. That proposal is still awaiting final approval.

In the new study, researchers from the Icahn School of Medicine at Mt. Sinai conducted an analysis of 46 previous studies on prenatal acetaminophen exposure and its relation to NDDs. 

They then ranked the studies based on risk of bias and quality of evidence, categorizing them as showing a positive association between Tylenol and NDDs, a negative association if the study showed that Tylenol seemed to help prevent developmental disorders, and a null association if the study found no significant association either way.

According to their findings, out of the 46 studies, 27 of them determined there was a positive association between acetaminophen use during pregnancy and ADHD, autism and similar disorders. Only four of the studies concluded Tylenol helped avoid NDDs, while nine studies found no associations at all.

Making the evidence of a positive association even stronger, the researchers noted that the higher-quality studies tended to be the ones that found a link between acetaminophen pregnancy use and children diagnosed with NDDs later in life.

Researchers also pointed to previous studies that found acetaminophen can pass through the placental barrier, with evidence suggesting it can cause oxidative stress, endocrine disruption and cause alterations to the neurotransmission system. This could be evidence of a mechanism of action, explaining how prenatal exposure could cause these types of disorders, the research team hypothesized.

“Appropriate and immediate steps should be taken to advise pregnant women to limit acetaminophen consumption to protect their offspring’s neurodevelopment.”

–Diddier Prada, Evaluation of the evidence on acetaminophen use and neurodevelopmental disorders using the Navigation Guide methodology

However, the researchers noted that maternal fever and pain pose their own risks, which still need to be addressed. Therefore, they recommend the lowest effective doses of acetaminophen for the shortest possible duration tailored to each woman’s individual risk assessments.