Science Friday - Is Tylenol Use During Pregnancy Connected To Autism?

Episode Date: September 26, 2025

At a news conference on September 22, President Trump claimed that taking acetaminophen, the active ingredient in Tylenol, during pregnancy “can be associated with a very increased risk of autism.�� Many experts have pushed back on the statement, saying it’s a false claim that downplays the risks of fever during pregnancy, which Tylenol may be used to treat.Autistic people and their families also raised concerns about the language used and the premise that autism is a scourge that needs to be eliminated.Host Flora Lichtman digs into what we know about acetaminophen use during pregnancy with epidemiologist Brian Lee, who led one of the largest peer-reviewed studies looking at the link between acetaminophen use during pregnancy and autism in children.Guest: Dr. Brian Lee is a professor of epidemiology at Drexel University, based in Philadelphia, Pennsylvania.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

This is Science Friday. I'm Flora Lickman. If you tuned into the news at all this week, you likely heard this new medical guidance from the Trump administration. Acetaminophen. Is that okay? Yes. Which is basically commonly known as Tylenol during pregnancy can be associated with a very increased risk of autism. So taking Tylenol, is not good. You may have also heard the backlash to this advice from many experts who disagree and worry about the risks of avoiding Tylenol during pregnancy.

And then there are concerns coming from the autistic community around the narrative that autism is inherently bad, a scourge that needs to be eliminated. And there are concerns that moms are being blamed for having autistic children. There is a lot to unpack. about genetics, about vaccines, but today I want to focus on the acetaminopin piece. If I saw these headlines while I was pregnant, I would want the nitty-gritty, where this idea came from, and what exactly researchers have found. So today, we are digging into the details with an epidemiologist who led one of the largest peer-reviewed studies looking at this exact question. What do we know about the link between acetaminopin and autism? Dr. Brian Lee is an epidemiologist,

at Drexel University and the senior author on a paper in JAMA about acetaminifin use during pregnancy and children's risk of autism and other neurodevelopmental outcomes. Brian, welcome to Science Friday. Hi, thank you for having me. So this Tylenol link to autism claim, you know, didn't come out of nowhere. You have looked at this association yourself. What made you decide to study this in the first place? Well, you know, acetaminopin is one of the,

most widely used medications in the world. And I think it is proper to question whether or not a medication during pregnancy is going to be safe. Our team looked at the available evidence. And basically, there are methodological limitations to the existing evidence that our study wanted to overcome. Before we get into your study, I mean, what was the available evidence? Because the fact sheet provided by the administration cites this review article, for example, from the Journal of Environmental Health that looks at over 40 studies and finds over half of them show

this association between taking Tylenol and pregnancy and autism. We invited one of those authors on the show, by the way, and she declined. But can you tell me a little bit about this review and what your reservations were about the evidence? Sure. So this review,

it's important to know it's just a new look at old existing studies. And they looked at some. somewhere over 40 studies of acetydominifin use and various neurodevelopmental outcomes. And the conclusion they came up with was that based on the available evidence, acetaminopin use during pregnancy was associated with increased risk of autism. The problem, however, is that association is not causation, right? Right. Okay. Let's talk about the study that you did.

What was your approach to this question? Yeah. So our study relied on looking at this amazing data resource of 2.5 million pregnancies, looking at the mothers and their children followed for over 20 years in Sweden. Importantly, we didn't ask a mom, hey, 20 years ago, what did you take during your pregnancy? Right. Like this is something that we were able to look at midwife interviews at their prenatal visits. where they asked questions about medication use, and we also had prescription drug records available. And then we also had the sort of electronic health record, but there's a couple missing pieces here, right? Like the reason you take acetaminopin is, you know,

like you have a headache, you have an infection fever, pregnancy pain, stuff like that, right? Is it going to be captured in data sources? Our data, for example, only captures receipt of clinical services. So if you just have a random headache, you're not necessarily going to go into the hospital to get that checked out, right? So you don't know why people are taking the Tylenol? Not necessarily, right? You can try and adjust for statistical differences with the data you have.

But if you don't have data on something, you can't adjust for it or account for it. Okay. And so these indications for use of acetaminopin, migraines, head. infection, fever, these sorts of things, incidentally, are associated with increased risk of autism. So there's already the possibility right there that it's not necessarily the acetaminopin that is increasing risk, but the reason you're taking it. Okay, let me see if I can sum that up. So one of the reasons why doing these epidemiological studies to try to untangle this link is one of the reasons that's difficult to do them is that you don't have data on why people

are taking the Tylenol. And the reason people might be taking the Tylenol also could be a risk factor for the outcomes that you're looking at. Exactly. So it basically comes down to this. What you want is an apples to apples comparison of the women who use acetaminopin versus the women who don't use. But users of medication are going to be different in many different ways from non-users. And the biggest thing, of course, is you don't take medication for fun. You're taking it for a health reason, right? And so the women who use acetaminin are going to be sicker in some way than non-users. And so what you're really doing then is an apples to oranges comparison. And this makes it challenging to look at the effects of acetaminopin on neurodevelopmental

outcomes. Okay. That's one of the challenges. How do you get around it? Yeah. And then I should mention the elephant in the room that people don't often talk about in these studies is genetics, right? So autism and other neurodevelopmental disorders, they are highly heritable. Interestingly enough, mom's genetic risk for neurodevelopmental disorders like autism and ADHD has also been linked with greater pregnancy pain, headaches, migraines, more use of pain relief medications, and, in fact, more use of acetaminopin. So if your genetic profile makes you more likely to have a child, you know, with autism because of genetics alone, you may also experience more pain in your pregnancy,

you know, that you might treat then with Tylenol. Exactly, right? So you can see this is a really complex issue because you're trying to isolate out the independent effect of acetaminifin, if there is one, right? But you have all of these other factors at play here. And in these large population-based studies, I actually mentioned that our study has, you know, 2.5 million pregnancies, the base. of most of these arguments by the administration are on studies, the largest caps out around like 50,000 pregnancies or so. But the basis of these studies, they usually do not have genetic information. We didn't either, but we were able to get around this with a statistical

approach. I think that's kind of interesting. So we actually have the entire population of Sweden at her disposal, we have family units where we can go and look for the families where there were one sibling who was exposed to acetaminifin in the womb and compare their outcomes to their unexposed sibling. And what happened was, you know, without the sibling control, we saw the exact same statistical association that, oh, acetaminin supposedly increases risk of autism. But when we did the sibling control analysis, that small statistical association completely flatlined, it disappeared. In other words, there was no evidence to support that acetaminopin causes autism. Okay. So you looked at families where there were multiple siblings, and these were pregnancies where the parent took Tylenol during one pregnancy, but not the other.

And then you compared to see, did those kids who were exposed to Tylenol, you know, in utero, did they have a higher likelihood of having autism than their sibling? And the answer was no. Exactly. Because if acetamin fin really does cause autism, then the sibling who is exposed to it should have a higher probability of autism than the sibling who is not exposed, right? Right. One of the findings of the review study cited by the administration is that it looked like dose mattered, that prolonged use of Tylenol in pregnancy. You know, taking Tylenol for over four weeks resulted in the stronger association with autism. Is that evidence of causation? This is one of those things where you could potentially look at it two different ways. Like, oh, yeah, if you take it for longer, that must, that's a clear, dose response, you know. But our take on this is that why are you taking it for longer? It's because you have more infection, you have more pregnancy pain, you just have more of that health condition, right? So, yeah, in my opinion, it doesn't strongly support the argument for causality.

How would you counsel a pregnant person in your family? You know, we know there are risks of not trading fevers during pregnancy. And at the same time, anyone who's been pregnant knows that so much of pregnancy is navigating these uncertainties. So what would you tell them? And do you think there's any reason for caution around using Tylenol when you're pregnant? I mean, I think caution is warranted for everything, right? Like, just because walking on the street is safe, statistically safe doesn't mean you shouldn't like keep your eyes open and watch out for the banana peel, right but you know bringing it back to acetaminophen like it the the strongest and best evidence available to date doesn't suggest that acetaminfant causes autism right but that doesn't mean of course

that you start popping acetaminopin like candy a seedaminopin has a known liver toxicity issue right and so i mean long story short the evidence to date suggests no causal effect of acedaminopin on autism, and folks can do with that what they will. I think that's the perfect place to leave it. Thank you for joining us today, Brian. All right. Thank you. Dr. Brian Lee is an epidemiologist at Drexel University who studies maternal medication used during pregnancy and child neurodevelopmental outcomes. I know this is a conversation that is so personal for so many of us and that there's so much misinformation around neurodivergence, which is

why we want to keep covering this on Science Friday. And we would like you in this conversation. What questions do you have about the science of autism? Call us 877 for SciFRI. Today's episode was produced by Rasha Aredi and

D. Peter Schmidt. But a lot of folks helped make this show happen every single week, including Jordan Smudjick. Emma Gomez. Valissa Mayors Santiago Flores I'm Flora Lichtman

Thanks for listening