Tylenol and the Fetal Brain

You may not be impressed by the solidity of the evidence behind President Trump’s warning this week that acetaminophen–one of its brand names is Tylenol (I’ll use its abbreviation APAP) during pregnancy is a potential cause of autism.  “Don’t take Tylenol,” he said, “Tylenol is not good. I’ll say it”  He also said some of his advisors wanted to be cautious with their words, but of himself he said: “I’m not so careful with what I say.”  And we’ve come to know that about the president. Anyway, I got looking around and I found this reel posted back in April. [Play the first 29 seconds of the reel]  Who is that handsome fella warning about APAP and pregnancy five months ago? He looks really familiar.  Augh!  It’ll come to me.

Whatever your impressions of this week’s announcement about APAP during pregnancy and autism, I’ve got something that WILL impress you.

I’m not going to review the data on APAP’s culpability for autism here today. I will do that in a future post.Today, I just want to acquaint you with the evidence that Tylenol can change brain development. Let’s start there.It’s an accepted fact in the field of child development that under normal conditions, boys are about twice as likely as girls to experience delayed speech by 30 months of age. This means fewer than 50 spoken words. It’s a milestone tracked by many pediatricians and researchers. But fairly recent research suggests that prenatal exposure to APAP can shrink this gender gap—not because boys are doing better, but because girls are doing worse.

In a 2018 Swedish study, researchers found that girls whose mothers used APAP more than six times per week during early pregnancy were significantly more likely to have delayed language development, while boys showed no significant increase in risk. This was a landmark study. The authors concluded that the usual sex difference where girls outperform boys in early language was blunted by APAP exposure.

This finding was replicated and extended in a study in 2024 which again found a stronger adverse association in females. Something is going on here and it involves the brain.

My point today is not about what APAP does to speech. I tell you about the changes in speech to demonstrate that the APAP makes it into the brain of a developing fetus. It has to because that’s where speech develops. So if it can subtly shift the trajectory of brain development in a sex-specific way, (because it happened to girls and not boys in the case of speech development), it’s not a big stretch to think that other mental or emotional functions could be affected by APAP exposure in a developing brain. And we need to be open to a link to autism. And in the meantime, I don’t think I want the women I love to use APAP during pregnancy.