Some suggest Tylenol is linked to autism. Here’s what to know.

Conservative media and influencers have seized on new research suggesting a connection between Tylenol use during pregnancy and autism, fueling online debate and calls for regulatory action in recent days.

Robert F. Kennedy Jr., secretary of the Department of Health and Human Services, has made autism a key focus of his “Make American Healthy Again” plan, and there has been speculation that his agency would emphasize the link in a highly anticipated report that is expected this month about efforts to uncover causes of autism. Public health experts have feared that Kennedy, an anti-vaccine activist, would also link autism to vaccines, a false claim that he has made repeatedly.

Shares of Kenvue, which makes Tylenol, fell 10 percent in late afternoon trading Friday following a report in the Wall Street Journal that HHS plans to mention the possibility that use of the pain reliever during pregnancy may be linked to the developmental disorder in offspring. An HHS spokeswoman declined to comment except to say that the department is “using gold-standard science to get to the bottom of America’s unprecedented rise in autism rates.”

About one in 36 children have an autism diagnosis, according to data from the Centers for Disease Control and Prevention — compared with one in 150 children in 2000. The reasons behind this sharp increase remain widely debated. Increased awareness and testing almost certainly play a role, but many researchers believe there are additional factors — likely something in our environment or lifestyles — at play in addition to the more than 100 genes that have been linked to the condition. Researchers have not found a link between vaccines and autism in dozens of studies across the globe.

Kenvue said leading medical groups have agreed that acetaminophen is safe to use during pregnancy. “We have continuously evaluated the science and continue to believe there is no causal link between acetaminophen use during pregnancy and autism,” the company said.

Proponents of Kennedy’s position have been actively pushing for more investigation into the common pain killer.

“What we might hear is something about the interaction of Tylenol in the very young together with things that are pro inflammatory, like, say, for example, multiple vaccination. That may be part of the issue associated with autism,” said Robert Malone this week on One America News to host and former Republican congressman Matt Gaetz.

It is unclear whether the September report will mention vaccines.

The recent interest in acetaminophen — the active ingredient in Tylenol — was ignited by a National Institutes of Health-funded study published Aug. 14 in BMC Environmental Health.

The new study, led by Icahn School of Medicine at Mount Sinai researcher Diddier Prada and colleagues at Harvard’s T.H. Chan School of Public Health, involved a rigorous review of 46 previously published epidemiological studies. Of these, 27 reported links between use of the medication by pregnant women and an increased risk of autism or ADHD in their children, 9 showed no link, and 4 indicated protective effects — with the higher quality studies more likely to show a connection.

Prada stressed that the findings do not prove a causal link.

“We show that acetaminophen is associated with a higher risk, but not causing it. Those are very different things,” he said in an interview.

David Kriebel, professor emeritus of public health at the University of Massachusetts at Lowell, said that although the evidence is “far from conclusive,” it is strong enough to warrant awareness. He said pregnant women may want to limit their use of acetaminophen and consult with their health care providers.

“There is a growing body of evidence suggesting we should be concerned about this possibility,” Kriebel said.

Both Kriebel and Zeyan Liew, an associate professor of epidemiology at the Yale School of Public Health, pointed to growing evidence from lab and animal studies suggesting that acetaminophen may negatively affect fetal development.

Liew said research suggests the possibility that high doses of the drug could interfere with the body’s hormone system or trigger oxidative stress — a condition where harmful substances build up and begin to damage cells.

“These are all unwanted biological effects that we don’t want happening during brain development,” Liew said.

“Tylenol came into the picture because its use very rapidly increased,” Liew said, “but it’s just one of many thousands of environmental factors we need to study.”

The current guidance on acetaminophen use by the American College of Obstetricians and Gynecologists is similar to that for all medications — which is to consult with their physicians.

But as far back as in 2021, 91 scientists, clinicians and public health professionals from around the world got together to urge stricter guidelines in a statement published in Nature Reviews Endocrinology. They recommended that pregnant women should be cautioned at the beginning of pregnancy to forego acetaminophen unless its use is medically indicated, consult with a physician or pharmacist if they are uncertain and before using on a long-term basis; and use the “lowest effective dose for the shortest possible time.”

In recent weeks, major anti-vaccine, right wing and MAHA influencers have been highlighting a link between Tylenol and autism.

Mentions of “Tylenol” were 15 times more common among MAHA influencers in August compared to April, according to a Post analysis of social media posts and podcasts from over 80 influencers.

Alex Clark, host of the popular Culture Apothecary podcast, tweeted “NEVER give your baby Tylenol” and discussed the potential harms of the drug in an episode of her show in August.

In a post on Facebook, Moms Across America, which has promoted the false idea that vaccines cause autism, wrote that higher acetaminophen exposure was linked to “3.5x the risk of autism” and encouraged followers to be “embracing the fever as a healing tool.” The post also advertised an herbal supplement with a custom discount code to take instead of Tylenol.

Children’s Health Defense, an anti-vaccine organization that Kennedy founded, has been spreading claims about a link between autism and vaccines for several years. Most recently, it has claimed that Tylenol is dangerous both during pregnancy and to newborns. This week it mischaracterized the results of the new study by writing on X, “They told us Tylenol was harmless. Now Harvard research shows an 80 percent spike in autism risk when used in pregnancy.”

In 2022, Kennedy himself shared an article calling for the end of acetaminophen use in infants and children as the authors claimed it was a potential driver of the “autism epidemic.”