Federal health officials are expected to link rising rates of autism to the use of acetaminophen, the active ingredient in the common painkiller Tylenol, in a report to be released on Monday. Scientists have studied a potential connection for years, but the research so far has yielded inconclusive results.
“I think it’s a very big factor,” President Trump told reporters on Sunday, referring to acetaminophen.
The agency plans to warn pregnant women against using acetaminophen except in case of fever, The Washington Post reported on Sunday. “If there’s a question — even if there’s a question — you just do it right?” Mr. Trump said to reporters aboard Air Force One.
Acetaminophen is considered one of the few safe options to treat pain or fever during pregnancy. Doctors already routinely warn pregnant women against long-term use.
This afternoon’s report also is expected to recommend a drug called leucovorin, a form of the B vitamin folate, which has long been known to influence neural development, as a possible treatment for autism.
Concerns about acetaminophen and developmental problems in children are longstanding. Yet scientists overwhelmingly agree that autism results from a complex mix of genetic and environmental factors, and rising rates cannot be ascribed to just one factor.
The federal report comes a month after a review of previous data, written by epidemiologists at the Harvard T.H. Chan School of Public Health and the Icahn School of Medicine at Mount Sinai, found evidence of a link between acetaminophen use during pregnancy and neurodevelopmental disorders like attention deficit hyperactivity disorder and autism.
Studies that have examined the possible risk posed to fetal brain development have been mixed. While some have found a link to neurodevelopmental disorders in children, others have not.
Many health agencies — including the Food and Drug Administration, the European Medicines Agency and the Society for Maternal-Fetal Medicine — have evaluated the evidence and decided that the findings are inconclusive.
Some scientists have recommended that health professionals take a precautionary stance and warn pregnant women about the possibility of a link between acetaminophen and autism.
But specialists in maternal-fetal medicine have argued that such a recommendation is unnecessary, because of existing guidance to pregnant women to use Tylenol and other drugs containing acetaminophen sparingly. They worry women might forgo treatment with acetaminophen when needed.
“There’s no credible scientific link that Tylenol causes autism,” said Dr. Nathaniel DeNicola, who advises the American College of Obstetricians and Gynecologists on environmental issues.
The studies that examine the connection are “too deeply and fundamentally flawed to draw reliable conclusions,” he said.
The authors of the latest report cautioned that their findings, too, did not prove a cause-and-effect relationship.
“We cannot answer the question about causation — that is very important to clarify,” Dr. Diddier Prada, an epidemiologist at Mt. Sinai and an author of the study, told The New York Times this month.
Because it would be unethical to perform pharmaceutical research on pregnant women, all of the existing research on the effects of acetaminophen are observational, meaning that researchers analyze data on women’s pregnancies and then look at how their children do over time.
As a result, researchers cannot account for all of the ways in which women who take Tylenol during their pregnancies may differ from the women who do not.
Many of the studies included in the new review “did not necessarily go to the greatest lengths to account for possible confounders,” Dr. Brian Lee, a professor of epidemiology at Drexel University, said, referring to other factors that might explain a potential link.
“And the biggest elephant in the room here,” he added, “is genetic confounding, because we know autism, A.D.H.D. and other neurodevelopmental disorders are highly heritable.”
In 2014, Dr. Lee was a co-author of a major study that analyzed the health records of 2.5 million children born in Sweden. While the study found a small positive association between women who used acetaminophen and the incidence of autism, A.D.H.D. and intellectual disability, that link disappeared after they did a subsequent analysis comparing siblings born to the same mothers.
The results of the sibling study indicated that the real cause could be “maternal genetics,” Dr. Lee said, not acetaminophen.
Pregnant women are already advised to consume folic acid — which leucovorin, the form of folic acid that the Health Department report is expected to recommend, is a form of — early in pregnancy to promote healthy brain development in the fetus.
Some studies have also suggested folic acid supplementation can improve behavioral outcomes, including communication, in children with autism, though those results are also preliminary.
Azeen Ghorayshi is a Times science reporter.
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