There is no link between acetaminophen in pregnancy and autism, according to a new study

A scientific review of 43 studies on acetaminophen use during pregnancy concluded that there is no evidence that the painkiller increases the risk of autism or other neurodevelopmental disorders.

“We did not find a clinically meaningful increase in the risk of autism, ADHD or intellectual disability,” said Dr. Asma Khalil, professor of obstetrics and maternal-fetal medicine at St George’s Hospital, University of London and lead author of the report, at a press conference. The study was published Friday in the British medical journal The Lancet.

Acetaminophen, the active ingredient in Tylenol, remains “the first-line treatment we would recommend if pregnant women experience pain or fever during pregnancy,” Dr. Khalil.

Studies that have examined a possible association between acetaminophen in pregnancy and a risk of neurodevelopmental disorders have provided conflicting data, with some finding no association and others finding a slight increase in risk.

The new scrutiny came after President Trump told pregnant women during a press conference in September to “hang in there” and “fight like hell” not to take Tylenol because he said the painkiller could cause autism in children. The message was delivered as part of a broader campaign by Health and Human Services Secretary Robert F. Kennedy Jr. to try to pinpoint the causes of rising autism rates among children in the United States, focusing on the unproven risks of acetaminophen and long-discredited theories that vaccines cause autism.

Medical groups around the world, including the American College of Obstetricians and Gynecologists, quickly disputed the president’s statements. They argued that doctors had already advised their pregnant patients to use paracetamol cautiously and warned that untreated fever during pregnancy could cause health problems for both mother and child.

Because acetaminophen enters the brain and also crosses the placenta during pregnancy, scientists have been studying its possible effects on fetal brain development for more than a decade.

It has been difficult to draw firm conclusions, in part because there are limited opportunities for scientists to study the question. Because of ethical concerns surrounding research on pregnant women, randomized, controlled clinical trials – the gold standard in medical research – have not been conducted.

Another obstacle is the ubiquity of paracetamol. It is known that other painkillers can cause serious harm during pregnancy, so paracetamol has long been recommended as a first-line treatment. And because it’s available over the counter, it’s difficult for scientists to track how often and when women use it.

A scientific review published last August by researchers at Harvard and the Icahn School of Medicine at Mount Sinai and cited by Trump’s health advisers in September concluded that there is evidence of a link between acetaminophen and autism.

However, some of the studies included in this review did not consider the underlying factors that might cause the association, Dr. Khalil. For example, women typically take acetaminophen because of health problems during pregnancy, including infections and fever, and these health problems themselves can increase the risk of neurodevelopmental disorders.

The new review excluded all studies that did not take such potential confounding factors into account. And there has been more emphasis on studies that have tried to explain the role of genetics by comparing siblings born to the same mother. Genetics are known to contribute significantly to the risk of autism.

“These were actually all attempts to derive evidence from high-quality studies,” said Dr. Khalil. The sibling studies are the most rigorously designed, she said, because they take into account shared genetic factors and a common family environment.

A large sibling study published in 2024 examined electronic health records of nearly 2.5 million children in Sweden and found a small association between women who used paracetamol and the occurrence of autism, ADHD and intellectual disability. But when the researchers then conducted an analysis comparing siblings where one was exposed to acetaminophen in the womb and the other was not, they found no connection.

Experts praised the new review for helping to better examine the different types of studies conducted to date. But some also warned that questions still remained unanswered. For example, the review did not take into account how often pregnant women took paracetamol and in what doses.

Eivind Ystrom, a senior researcher at the Norwegian Institute of Public Health, said he supported the new review’s conclusion “given our current knowledge.” But he added: “At the same time, we should do more and better studies.”

Dr. Ystrom conducted a study in 2021 suggesting that pregnant women who take acetaminophen for longer than 29 days may be at higher risk of having children with ADHD

Andrew Nixon, a spokesman for the Department of Health and Human Services, said: “Many experts have expressed concerns about the use of acetaminophen during pregnancy.”

The new scientific review comes amid ongoing legal battles over the possible link between acetaminophen and neurodevelopmental disorders. Hundreds of lawsuits have been filed in recent years against the makers of Tylenol and its generic versions by families claiming their children developed autism or ADHD after the mothers took the painkiller during pregnancy. The largest group of lawsuits filed in federal court was dismissed by a judge in 2023, citing a lack of credible scientific evidence. This decision is being appealed.

And in October, Ken Paxton, the Republican attorney general of Texas, sued Johnson & Johnson, which made the drug for decades, and Kenvue, a spinoff company that has sold it since 2023, claiming the companies concealed the drug’s risks to children’s brain development.