Does Tylenol (acetaminophen) cause autism?
John Williams
Donald Trump thinks so, but the evidence is not clear. Some people talk as if the association between utero exposure to acetaminophen and autism spectrum disorder (ASD) had been established, and others as if it had been refuted. In fact, some studies have found such an association, but others have not, and an association does not show causation.
There are problems with the evidence either side points to. The White House points to a statement by the Dean of the Harvard School of Public Health, which seems like it should carry considerable weight, but then it turns out that he made $150k as an expert witness in unsuccessful litigation, and, according to the NY Times:
In the decision to dismiss the lawsuits, the judge, Denise Cote, agreed with lawyers for the defendants that Dr. Baccarelli had “cherry-picked and misrepresented study results” in his testimony and was therefore “unreliable.”
On the other hand, people who want to argue against the association point to a Swedish study that has an obvious weakness.* However, acetaminophen is used to treat fever, and fever in pregnant women is also linked to problems in developing fetuses, so not taking acetaminophen can have its own risks. On balance, probably it makes sense for pregnant women to be careful about taking acetaminophen, but not too careful. Here is how one of the studies cited by the White House puts it:
While this association warrants caution, untreated maternal fever and pain pose risks such as neural tube defects and preterm birth, necessitating a balanced approach. We recommend judicious acetaminophen use—lowest effective dose, shortest duration—under medical guidance, tailored to individual risk–benefit assessments, rather than a broad limitation.
Notably, that Harvard dean was the senior author on this study.
*For those interested in such things, the problem with the Swedish study is that, like all such studies, it does not have data on the amount of acetaminophen pregnant mothers actually took, but rather with their reports of how much they took. In this case, an unrealistically small percentage of the mothers reported that they took acetaminophen (7.5%, when other evidence suggests that likely it was more like 40% or 50%). This doesn’t mean that the findings of the study are wrong, but it does mean that they could be.