The use of acetaminophen in babies and in children would never have been approved if it had been tested using current safety standards, claims William Parker, Ph.D.

Parker, who is based in Durham, North Carolina, is an immunologist and biochemist. He conducted research and taught medical school students at Duke University for more than 25 years. He and his colleagues have been researching and writing about the effects of acetaminophen—which is the main ingredient in Tylenol—since 2015.

Acetaminophen Linked to Autism ‘With No Reasonable Doubt’

In one of his most recent studies, co-authored with six other Ph.D. scientists, Parker and his team concluded: “with no reasonable doubt” that acetaminophen causes autism in susceptible babies and children.

“Let me be clear,” Parker told us. “This is not a hypothesis. We have enough evidence for a conclusion on this issue.”

The peer-reviewed study was published in July 2022 in the Italian journal Minerva Pediatrics. The co-authors included two scientists in the pharmaceutical industry as well as Dr. Kate Reissner, a professor and neuroscientist at the University of North Carolina.

“Our published conclusion is based on 17 lines of evidence,” Parker explained. That evidence includes small but compelling studies in humans, numerous studies in animal models, and a series of clues that all point toward acetaminophen as a cause of autism.

“Under normal circumstances, if a drug causes permanent behavioral changes in laboratory animals, it will never be tested in humans,” Parker explained. “Those are called pre-clinical trials. If you fail in pre-clinical trials, then they would never try it in a baby human, if it’s hurting baby animals.”

Indeed, he has conducted his own studies in laboratory animals showing that acetaminophen is not safe, even when used as currently accepted for human babies. In addition, he pointed to a particularly compelling study by Henrik Viberg, a Swedish scientist, who showed that just two doses of acetaminophen at a very young age cause laboratory mice to lose their ability to learn later in life.

Why Do Pediatricians Still Recommend Infant Tylenol?

Given the growing body of scientific evidence linking acetaminophen to autism, as well as the continued rise in autism rates in the United States and other countries in the industrialized world, why do most pediatricians think acetaminophen is safe for babies and children?

“There are several reasons,” Parker explained when we asked him this question. “It’s thought to be safe by almost everyone, that leads to a consensus bias. Moreover, most children don’t become autistic after taking acetaminophen, which leads to an antidote bias. That’s: ‘hey my grandma smoked all her life and never got lung cancer and lived to 102, so smoking isn’t bad for you.’”

But the real reason, Parker said, is that public health authorities report that it is safe.

“The bottom line is that we just can’t expect a typical pediatrician will know anything regarding the safety of drugs for children beyond what they are told by regulatory agencies,” Parker said. “People assume that the doctors know the latest research, but that’s not their job.”

Parker pointed out that pediatricians are busy seeing patients. So, they rely primarily on regulatory agencies, in particular the FDA and the CDC, to tell them what is safe.

Most pediatricians are not aware that boys who are circumcisedhave twice the prevalence of infantile autism as boys who are not. The connection between circumcision, a surgical procedure that often involves the administration of acetaminophen, and autism are one of the 17 lines of evidence compiled by Parker and his team that led them to conclude that acetaminophen causes autism in susceptible children. But that clue is not common knowledge among pediatricians because neither the FDA nor the American Academy of Pediatrics have issued any warnings about it.

At a pediatric conference in Medford, Oregon, that Jennifer attended several years ago, this question was put to a pediatrician, a tongue-tie specialist based in Portland, Oregon. In his talk, as well as on his website, he specifically stated that parents may use Tylenol post-frenotomy.

Though he admitted publicly that he was aware of the evidence linking Tylenol to autism spectrum disorders, the doctor told the audience of about a hundred Oregon healthcare professionals that there was no other painkiller to recommend, as ibuprofen is not approved for children under six months.

Wrongly Assumed Safe

A team of researchers from Duke University and the University of Montreal reviewed the history of how and why acetaminophen was approved for use in infants, given its very concerning safety record. That peer-reviewed study, published in May 2022 in the European Journal of Pediatrics, explained that acetaminophen was assumed to be safe for babies and children in the 1960s and 1970s because it was found to be safe for a baby’s liver.

The underlying assumption, now known to be false, was that babies and children process drugs the same as adults do. Since acetaminophen damage manifests as liver damage in adults, investigators decided to check for liver function in babies as their only measure of safety. 

“In hindsight, the mistake is obvious,” Parker said. “Nobody ever checked to see if it was causing damage to the baby’s brain. But now we know it does if the child is susceptible.”

More Than a Decade of Research

Are Parker and the scientists working with him rushing to a premature conclusion? Are they overstating their concerns? Are they confusing correlation with causation?

In response to these questions, Parker laughed. Then he launched into a litany of facts:

• The first paper that showed acetaminophen causes autism was published in 2008, well over a decade ago. 
• His first review on the topic, with scientists and clinicians at Duke and Harvard, was published more than five years ago.  
• Among other things, he points out that it took almost three years to complete and publish his study showing when, where, and how the tragedy happened.

“Scientists have been known to rush to a speedy conclusion on occasion,” Parker insisted. “This is not one of those occasions. This pile of evidence is so ripe that it will explode.”

Wrong Focus

In 2020, Johnson & Johnson was ordered to pay $6.3 million for misleading advertising on the packaging of infant Tylenol. Since then, at least 20 lawsuits against Tylenol have been filed, many of them highly publicized.

While the media attention surrounding these lawsuits is bringing important issues to light, Parker said, he believes that the lawsuits may also mislead the public.

Here’s why: these lawsuits are focused on acetaminophen use during pregnancy. But Parker and his colleagues believe that acetaminophen use in babies and in children probably is much more dangerous than acetaminophen use during pregnancy.

“Post-natal use probably causes five or six times more cases of autism than use during pregnancy,” he said.

Could We Make Tylenol Safe?

Parker said it’s very difficult to know in advance what children are more susceptible to brain injury from acetaminophen. He said genetic factors play a role.

Other doctors, including Ben Lynch in Washington and Paul Thomas in Oregon, have said that children who are homozygous for MTHFR mutations are more likely to have difficulty detoxifying. But, Parker said, a variety of other factors—including a depleted microbiome and co-existing autoimmune dysfunction—can stress the immune system.

In December 2015, two medical scientists from the University of Miami found that letting a fever “ride” was supported by several randomized controlled studies. Five months later, a long review article published in Nature Reviews Immunology showed that most fevers are protective, and many should be allowed to run their course. 

There are many natural alternatives to acetaminophen, some of which can be safely given to infants. But Parker also has another suggestion. He said that adding an antidote for the drug’s toxicity might be a way to make it safe.

One such antidote, acetylcysteine, Parker said, is usually well tolerated. “We shouldn’t assume it will work,” he said, “but we could test it easily enough.”