On Monday (Sept. 22), President Donald Trump warned pregnant people to avoid acetaminophen, the active ingredient in Tylenol, because of a controversial study by a Harvard dean and others. In response, several health organizations — including the American College of Obstetricians and Gynecologists (ACOG), the Society of Obstetrics and Gynecology of Canada, the American Academy of Pediatrics (AAP) and the World Health Organization (WHO) — have issued statements rebutting Trump's assertion that Tylenol use in pregnancy "can be associated with an increased risk of autism."
Trump also advised parents not to give Tylenol to babies, prompting the AAP to issue a statement saying, "decades of research have found that acetaminophen is safe for children when administered as recommended. Misleading claims that the medicine is not safe and is linked to increased rates of autism send a confusing, dangerous message to parents and expectant parents."
Have any studies found a causal link between acetaminophen use in pregnancy and autism?
No, according to the WHO, ACOG and AAP. No studies have shown that acetaminophen causes neurodevelopmental issues.
While health experts advocate limiting acetaminophen use in pregnancy to only when necessary, some of the most reassuring data comes from a 2022 study in the journal The Association for Child and Adolescent Mental Health and a 2024 JAMA study that looked at nearly 2.5 million Swedish children born between 1995 and 2019. Both found no causal link.
The Swedish study found a marginal statistical association between a pregnant person's use of acetaminophen and an increased risk of autism and attention-deficit hyperactivity disorder (ADHD). But that association disappeared once siblings in the same family whose mothers either did or did not take acetaminophen were compared, lead author Brian Lee, an epidemiologist at Drexel University's Dornsife School of Public Health, wrote in an email to Live Science.
That makes it unlikely that acetaminophen causes autism. Rather, there are other factors, or confounders, that both make people more likely to take the pain reliever during pregnancy and more likely to have a child with autism. "Association is not causation," Lee said.
What's likely behind the association is that people who take acetaminophen are doing so to treat a medical condition such as an infection, fever, headache or migraine, and "all of these factors have been found to be associated with risk of autism in the child," Lee said.
What's more, scientists know there's a large genetic component to autism, and women with genes that raise the risk of neurodevelopmental disorders tend to report more pregnancy pain and use of acetaminophen. That same genetic risk of a neurodevelopmental disorder is passed on to their child, Lee added.
Nevertheless, on Sept. 22, the U.S. Food and Drug Administration announced that it will issue a physician notice and initiate a safety label change for acetaminophen, while the U.S. Department of Health and Human Services (HHS) will launch a public service campaign, HHS announced.
If data doesn't show that acetaminophen use during pregnancy causes autism, where did that idea originate?
As evidence for their claims, Trump administration officials cited an August analysis co-authored by epidemiologist Dr. Andrea Baccarelli, dean of Harvard's T.H. Chan School of Public Health, that combined data from many studies on acetaminophen and neurodevelopmental disorders.
The New York Times reported that Baccarelli was paid $150,000 as an expert witness for plaintiffs in lawsuits against Tylenol makers — testimony that was ultimately thrown out for being scientifically unsound. Lee, for his part, is very skeptical of the study.
"Unfortunately, in this instance, the review of the paper was done so blatantly poorly that one has to question the objectivity of the authors," Lee wrote in an email.
Baccarelli's work "cherry-picked and misrepresented the literature," underweighting studies that accounted for issues like genetics or maternal health that may raise the risk of autism, while overweighting studies that did not account for those factors, Lee explained.
The flaws in Baccarelli's study are similar to those that bedeviled early work that suggested drinking coffee caused lung cancer. This was a problem because people who smoke tend to drink a lot of coffee, he said. If you did a study that did not adjust for smoking, you would conclude that coffee causes lung cancer, when it's actually the smoking that does.
"The exact same thing is going on here," Lee said.
What is acetaminophen used to treat in pregnancy?
Acetaminophen is one of the most commonly used medications during pregnancy around the world, according to Nature. Not only can acetaminophen benefit the pregnant person by reducing pain and fever, according to Nature, but it may also prevent negative health consequences for the fetus that might otherwise arise due to maternal symptoms.
Are there any safe alternatives to acetaminophen for pregnant people?
There are very few alternatives to acetaminophen for pain relief and treatment of fevers or headaches during pregnancy. That's because many would-be alternatives — including nonsteroidal anti-inflammatory (NSAIDs) drugs, such as ibuprofen (Advil), naproxen (Aleve) and aspirin — come with usage restrictions or contraindications, according to ACOG. Acetaminophen is recommended for prudent use following consultation with a doctor and is readily available to most people who need it.
If acetaminophen doesn't work, ibuprofen and naproxen can be taken for migraines in the second trimester only and for no more than 48 hours at a time, ACOG says. Taking NSAIDs in the third trimester may lead to birth defects, according to ACOG.
Low-dose aspirin has been used in special cases, most commonly to reduce the risk of or delay the onset of preeclampsia, according to ACOG clinical guidelines. Low-dose aspirin has also been used to treat recurrent miscarriage and fetal growth restriction, according to a 2021 study in the journal Human Reproduction Update.
What are the dangers of fever if left untreated during fetal development?
A systematic review and meta-analysis in the journal Molecular Autism reviewed 10 studies involving 10,304 children with neurodevelopmental disorders such as autism, ADHD and intellectual disability and found that fevers during pregnancy were tied to an increased risk of neurodevelopmental disorders in children. One relatively small study found that when pregnant people with influenza have a fever, their odds of having a child with autism were lower if they took a fever reducer versus if they didn't. This hints that an underlying issue, such as fever or infection, may be a factor in the increased risk for neurodevelopmental disorders in children.
