I’ve seen a lot of scary panic headlines — maybe even a lawsuit? — about exposure to Tylenol during pregnancy. Is it okay to treat my headache?
—Head pain and Pregnant
This question has been coming up for years. I’ve written about it before, and it’s the subject of an active lawsuit. The problem with most of the evidence on this is that it is very difficult to separate correlation from causality. Women who take Tylenol tend to be different from those who do not — on top of the concern that whatever is necessitating the Tylenol might be responsible. In all prior writing on this, the conclusions are a little unsatisfying, because we suspect these are just correlations but cannot say with certainty.
This has changed. Just this week a new paper on it was released, with better-quality evidence. The paper, published in JAMA, uses a sibling analysis to address this question. We all know that the “gold standard” for causality is a randomized controlled trial. But that is not going to happen in this case, for many reasons. A sibling analysis isn’t as good as a randomized trial, but it’s a huge improvement over just comparing across kids. In short, this paper compares kids born to the same mother, where she took Tylenol in one pregnancy and not the other. Because this analysis holds the mother constant, it is able to adjust for all of the characteristics of the mom — the ones we can measure and the ones we do not. This is able to effectively turn off many of our most significant concerns about a relationship being just correlation.
The paper uses an enormous sample of people — 2.5 million births in Sweden; that’s all singleton births in Sweden between 1995 and 2019. Women were asked about acetaminophen use several times during pregnancy, and diagnoses of children are measured in medical records (Scandinavian data is extremely complete).
The results: When the authors do a naive analysis, where they do not compare within siblings — this is similar to the existing literature — what they find is consistent with what has been found before: a modest increase in ADHD and autism rates among children whose mothers were exposed to acetaminophen during pregnancy. However, when they do their sibling analysis, they find this result completely goes away. This is their most compelling analysis, and the result is: there is no relationship between acetaminophen exposure and these diagnoses.
This is true when they measure any exposure and when they measure higher exposure amounts. Without sibling controls, higher exposure looks like it leads to more diagnoses. With sibling controls, higher exposure has no impact.
This is extremely good news for pregnant people. In the best data we have, which is now quite good, there is no link between Tylenol exposure and these behavioral outcomes for kids. If you have a headache, please treat it.
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