Does taking paracetamol in pregnancy cause autism? A look at the research evidence.

The question of a relationship between acetaminophen (paracetamol/tylenol) and autism has received a lot of attention in the media and social media. Many health focused organisations have commented on the evidence or lack of evidence for the link but I have seen very little coverage of the actual research studies behind this discussed link. So here is an overview of some key studies.

The link between acetaminophen and autism did not come out of nowhere. There are multiple studies that have shown a link between the two. But this is where we need to be cautious. There can be a link between two items, including a statistically significant association, but that does not necessarily mean one causes the other.

A classic example is the relationship between ice-cream and sunburn – the more sunburnt people get the more ice-cream is eaten. But eating ice-cream didn’t cause the sunburn – it was caused by another factor that influences both of them occurring – it being summer.  When another factor can explain a relationship we call it a ‘confounding’ factor in research. This highlights why we always have to be cautious when interpreting findings unless all potential factors have been controlled or accounted for in some way.   Read our top tip guide for information on correlation and causation.        

When we look at studies that have examined acetaminophen and autism it is clear that the studies cannot rule out other factors that may be explaining an association found. A recent study of 2.5 million children in Sweden showed that use of acetaminophen by the mother in pregnancy was associated with a marginally increased risk of autism, ADHD (Attention Deficit Hyperactivity Disorder) and intellectual disability. But when the researchers conducted ‘sibling control analyses’ the association disappeared. Doing this type of analysis on full siblings means that the researchers can control for characteristics related to the family that may be impacting the findings. We know that autism and ADHD run in families. This means children who are autistic or have ADHD are more likely to have a parent who has one or more of these conditions than you would see in the general population.

There is evidence that mothers who use acetaminophen during pregnancy reported higher prevalence of multiple health conditions that are associated with autism and ADHD in comparison to mothers who did not take acetaminophen. The answer it comes back to then is that autism and ADHD runs in families. There may be several confounding factors explaining the link rather than the actual acetaminophen itself such as mothers who are autistic or have ADHD being more likely to take this medication. Factors associated with being autistic or having ADHD such as increased risk of migraine means they may take more medications like acetaminophen.

The studies on this topic have shown inconsistent findings – some finding links between acetaminophen and autism and ADHD and others not. This suggests sample differences between the studies at least in part influencing the study outcomes. It is also important to note that historically women have been late diagnosed, mis-diagnosed and often completely missed for autism and ADHD diagnoses. This means these study samples likely have mothers with higher rates of these conditions than is reported.

Another set of researchers recently published a review on this topic. They took a cautious critical approach to reviewing the literature. They also found the familial confounding effect when controlled for through sibling analysis as described above. They also identified significant biases within studies such as the way the samples were selected to take part in studies.

Bottomline is we know that autism and ADHD run in families. These conditions have not appeared out of nowhere over the last decade or so as we are seeing media reports of. There is much better awareness of these conditions especially in girls. And with early support crucial for long term developmental outcomes including education, having a job, wellbeing and mental health it is critical we focus our energies on supporting these families and all those who care for these children, young people and as they grow in adulthood.