Why are autism rates rising? It’s not Tylenol

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Lester Liao is a developmental pediatrician and assistant professor at the Montreal Children’s Hospital and McGill University. His academic work focuses on medicine and culture.

Rates of autism have been increasing over the past several decades. Canadian data suggest one in 50 children and youth has autism spectrum disorder. Recent surveillance data from the U.S. Centers for Disease Control and Prevention suggest that one in 31 American eight-year-olds has ASD.

So what’s the cause?

A hypothesis that links ASD and acetaminophen (also known as paracetamol, or most commonly, Tylenol) has recently come to the fore, thanks to the Trump administration, which took the highly unusual step on Monday of directly advising parents and caregivers against using Tylenol during pregnancy and childhood. Some studies have indeed noted associations between prenatal use of acetaminophen and ASD (though others have not); it merits repeating that association does not equal causation.

Further scientific exploration is reasonable and lies at the heart of all good scientific curiosity. It does not appear that such claims are mere shams, which would not be new in the history of autism and its causes. But acetaminophen is not causing the autism epidemic, and placing so much weight on this medicine is unwarranted – not just because the evidence is lacking, but because there are, frankly, better explanations. Indeed, the rise of ASD diagnoses is best explained by a combination of diagnostic developments and cultural factors.

From a clinical standpoint, a significant change occurred when the idea of autism as a spectrum was introduced in the Diagnostic and Statistical Manual of Mental Illnesses, or DSM-5. While the criteria are intended to provide boundaries around diagnoses and create a systematic process, there remain ambiguities such as “functional impairment,” and practical questions around where to draw the line on a spectrum. As a whole, it has become easier to make a diagnosis.

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Standardized tools have been developed to help with diagnostic cut-offs, but the training in the use of those tools has itself become problematic. Clinicians have become overindexed to scores derived from these tools, rather than using them as one measure, and there can be a lack of understanding around the limitations of specific tools within certain populations.

Yet there’s another phenomenon, and it is a cultural one: Patients are now actively seeking autism diagnoses, relating to the broader neurodiversity movement in Western cultures. In our pluralistic culture, we increasingly emphasize meaning through identity, and neurodiversity meets this in part. In this context, one does not have ASD, but rather is autistic; this allows a person to form an identity without necessarily having a disorder, belong to a social group, and still emphasize their unique traits and needs.

This is not like ASD as it was diagnosed just decades ago. Classic ASD diagnoses were reserved for children with significant needs – for instance, a non-speaking seven-year-old who was completely isolated and engaged hourly in self-injurious behaviour. Those diagnoses came because parents were seeking help for their children, not because people were seeking identities for themselves.

Trends point to recent diagnoses of autism being milder. It isn’t unusual to see a young adult with some social difficulties and strong interests being diagnosed with ASD today. Yet these children’s needs are very different. It is why the concept of neurodiversity has been polarizing. It can be belittling for many families to take a diagnosis of severe autism and now speak of it as an identity as opposed to a genuine disorder.

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There is another group that seeks diagnoses: increasingly vigilant parents of younger children. Screening programs that emphasize ASD-related symptoms are now ubiquitous. Worried parents show up if a child exhibits a particular behaviour, and even if the parents aren’t so involved, children are often flagged by educators for showing “atypical” behaviours.

Sometimes this is helpful; often it is not. Because of this approach, traits have been medicalized – a defect in the translation from clinical experts to mass screening and education programs.

So what if access to additional supports hinging on a diagnosis, the incorrect use of diagnostic tools, blurrier diagnostic lines, and the rise of dubious private clinics willing to make diagnoses to satisfy customers are all added to the mix? You have the perfect storm that leads to diagnostic inflation.

It is unquestionable that ASD diagnoses are more common. But it is not primarily because of acetaminophen. Nor is it even necessarily because people have changed. Rather, we have shifted how we as a society use the term autism – and how we relate to it, too.