The Very Common Painkiller Linked to Autism and Hyperactivity in Children

A new study links one of the world's most popular painkillers to an increase in autism spectrum and hyperactivity symptoms.

Acetaminophen has been coming under increased scrutiny from the scientific community for a variety of possible side effects, including a recent study about its effect on empathy. Now, new research comes out that shows a possible relationship of acetaminophen use by pregnant women to autism spectrum and hyperactivity symptoms in their children.


Acetaminophen is used as an ingredient in over 600 medications like Tylenol or Paracetamol and is commonly used during pregnancy (taken by around 65% of expectant mothers in the U.S.) The study by Spanish scientists found that its use was linked to an increase of 2 clinical autism spectrum symptoms in boys and an increase of 30% in the risk for attention deficit symptoms for both boys and girls. 

The research involved 2644 mother-child pairs who were evaluated when the child was one and five. The mothers were asked about their use of acetaminophen.

Around 40% of the women took acetaminophen at some point during their first 32 weeks of pregnancy and their children showed a higher risk of a variety of symptoms.

Claudia Avella-Garcia, researcher at CREAL in Barcelona, elaborated that:

"although we measured symptoms and not diagnoses, an increase in the number of symptoms that a child has, can affect him or her, even if they are not severe enough to warrant a clinical diagnosis of a neurodevelopmental disorder."

How could the drug make this happen?

The study other author, Dr. Jordi Júlvez from CREAL, explained:

"Paracetamol could be harmful to neurodevelopment for several reasons. First of all, it relieves pain by acting on cannabinoid receptors in the brain. Since these receptors normally help determine how neurons mature and connect with one another, paracetamol could alter these important processes. It can also affect the development of the immune system, or be directly toxic to some fetuses that may not have the same capacity as an adult to metabolize this drug, or by creating oxidative stress."

As far as why boys could be more likely to exhibit autism spectrum symptoms, Claudia Avella-Garcia added: 

"The male brain may be more vulnerable to harmful influences during early life. Our differing gender results suggest that androgenic endocrine disruption, to which male brains could be more sensitive, may explain the association."

The scientists ultimately concluded that exposing unborn children to acetaminophen through medicines like Tylenol could increase the number of kids with autism spectrum symptoms and ADHD. But more studies are needed to confirm this relationship, especially ones where precise dosage could be tracked.

This was the one major criticism of the study as voiced by Dr. James Cusack of a U.K. autism charity. He points out that

"The results presented are preliminary in their nature, and so should not concern families or pregnant women. As the authors correctly state, more research, with careful control for other factors is required to understand whether a link exists at all."

Dr. Cusack further focuses on the fact that the study involved asking people to recall how they used the acetaminophen, a rather inexact method. 

However, there have been other studies that showed potential concerns like the 2013 Norwegian study that involved over 48,000 kids and found that children of women who took acetaminophen while pregnant were 70% more likely to exhibit brain abnormalities and developmental delays.

A 2014 Danish study that tracked 64,000 children and similarly found that those whose moms took acetaminophen during pregnancy were more likely to have attention deficit disorders, which increased in severity with the amount of the drug taken.

A further analysis of the same data resulted in the 2015 paper by mostly the same scientists that showed more specifically an increased risk of autism spectrum symptoms with accompanying hyperactivity. 

The makers of Tylenol are understandably disputing these studies, saying that none of them currently show:

“a causal link between acetaminophen use during pregnancy or in childhood and adverse effects on child development, including autism.”

There has also been additional criticism of the study from some scientists like Dr James Cusack, director of science at the autism research charity, Autistica, who said:

"This paper does not provide sufficient evidence to support the claim that there is a strong association between paracetamol use and the presentation of symptoms of autism. Rather, the results presented are preliminary in their nature, and so should not concern families or pregnant women. This is particularly true given the array of environmental factors which have been associated with autism, only to be rejected later."

Additionally, Professor Alan Cameron, vice president of clinical quality at the Royal College of Obstetricians and Gynaecologists, pointed out:

"Paracetamol is one of the most common medicines used to reduce a high temperature and ease pain; it is safe and is used routinely during all stages of pregnancy.

"The preliminary results from this study suggest that frequent paracetamol use throughout pregnancy may impact attention function and slightly increase the risk of hyperactivity in the offspring at aged 5 years old. No effect on cognitive, motor or social development was identified.

"It is important to highlight that from these results we cannot determine a direct link between paracetamol usage and any neurodevelopmental problems. Future studies should take into account dosage as well as other possible contributory factors.

"However, women should not be alarmed by the results of this study and we recommend that pregnant women continue to follow cucurrent guidance and take the lowest effective dose for the shortest possible time when necessary."

While the jury is still out on acetaminophen, you can read the full Spanish study here in the International Journal of Epidemiology.

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Homo sapiens have been on earth for 200,000 years — give or take a few ten-thousand-year stretches. Much of that time is shrouded in the fog of prehistory. What we do know has been pieced together by deciphering the fossil record through the principles of evolutionary theory. Yet new discoveries contain the potential to refashion that knowledge and lead scientists to new, previously unconsidered conclusions.

A set of 8-million-year-old teeth may have done just that. Researchers recently inspected the upper and lower jaw of an ancient European ape. Their conclusions suggest that humanity's forebearers may have arisen in Europe before migrating to Africa, potentially upending a scientific consensus that has stood since Darwin's day.

Rethinking humanity's origin story

The frontispiece of Thomas Huxley's Evidence as to Man's Place in Nature (1863) sketched by natural history artist Benjamin Waterhouse Hawkins. (Photo: Wikimedia Commons)

As reported in New Scientist, the 8- to 9-million-year-old hominin jaw bones were found at Nikiti, northern Greece, in the '90s. Scientists originally pegged the chompers as belonging to a member of Ouranopithecus, an genus of extinct Eurasian ape.

David Begun, an anthropologist at the University of Toronto, and his team recently reexamined the jaw bones. They argue that the original identification was incorrect. Based on the fossil's hominin-like canines and premolar roots, they identify that the ape belongs to a previously unknown proto-hominin.

The researchers hypothesize that these proto-hominins were the evolutionary ancestors of another European great ape Graecopithecus, which the same team tentatively identified as an early hominin in 2017. Graecopithecus lived in south-east Europe 7.2 million years ago. If the premise is correct, these hominins would have migrated to Africa 7 million years ago, after undergoing much of their evolutionary development in Europe.

Begun points out that south-east Europe was once occupied by the ancestors of animals like the giraffe and rhino, too. "It's widely agreed that this was the found fauna of most of what we see in Africa today," he told New Scientists. "If the antelopes and giraffes could get into Africa 7 million years ago, why not the apes?"

He recently outlined this idea at a conference of the American Association of Physical Anthropologists.

It's worth noting that Begun has made similar hypotheses before. Writing for the Journal of Human Evolution in 2002, Begun and Elmar Heizmann of the Natural history Museum of Stuttgart discussed a great ape fossil found in Germany that they argued could be the ancestor (broadly speaking) of all living great apes and humans.

"Found in Germany 20 years ago, this specimen is about 16.5 million years old, some 1.5 million years older than similar species from East Africa," Begun said in a statement then. "It suggests that the great ape and human lineage first appeared in Eurasia and not Africa."

Migrating out of Africa

In the Descent of Man, Charles Darwin proposed that hominins descended out of Africa. Considering the relatively few fossils available at the time, it is a testament to Darwin's astuteness that his hypothesis remains the leading theory.

Since Darwin's time, we have unearthed many more fossils and discovered new evidence in genetics. As such, our African-origin story has undergone many updates and revisions since 1871. Today, it has splintered into two theories: the "out of Africa" theory and the "multi-regional" theory.

The out of Africa theory suggests that the cradle of all humanity was Africa. Homo sapiens evolved exclusively and recently on that continent. At some point in prehistory, our ancestors migrated from Africa to Eurasia and replaced other subspecies of the genus Homo, such as Neanderthals. This is the dominant theory among scientists, and current evidence seems to support it best — though, say that in some circles and be prepared for a late-night debate that goes well past last call.

The multi-regional theory suggests that humans evolved in parallel across various regions. According to this model, the hominins Homo erectus left Africa to settle across Eurasia and (maybe) Australia. These disparate populations eventually evolved into modern humans thanks to a helping dollop of gene flow.

Of course, there are the broad strokes of very nuanced models, and we're leaving a lot of discussion out. There is, for example, a debate as to whether African Homo erectus fossils should be considered alongside Asian ones or should be labeled as a different subspecies, Homo ergaster.

Proponents of the out-of-Africa model aren't sure whether non-African humans descended from a single migration out of Africa or at least two major waves of migration followed by a lot of interbreeding.

Did we head east or south of Eden?

Not all anthropologists agree with Begun and his team's conclusions. As noted by New Scientist, it is possible that the Nikiti ape is not related to hominins at all. It may have evolved similar features independently, developing teeth to eat similar foods or chew in a similar manner as early hominins.

Ultimately, Nikiti ape alone doesn't offer enough evidence to upend the out of Africa model, which is supported by a more robust fossil record and DNA evidence. But additional evidence may be uncovered to lend further credence to Begun's hypothesis or lead us to yet unconsidered ideas about humanity's evolution.