Autism and Tylenol: Should We Be Concerned?

AI Tylenol Bottle with Gibberish Text

A couple days ago we were told by Trump and RFK jr that we should be concerned about a potential causal link between Tylenol use during pregnancy and autism spectrum disorder (ASD). Given that Tylenol is pretty much the only over-the-counter medication that is considered safe to take for fevers and pain during pregnancy, I can only imagine the confusion being generated right now about how to cope with pain and fever during pregnancy. Now I'm not a medical doctor, so please don't just take my word for it. I'll supply a series of links below to resources written by those qualified to give medical advice. I think, however, we should be able to see through a lot of the current rhetoric if we understand how both cherry picking and ignoring confounding variables can lead to very misleading conclusions that can result in needless fears and even false guilt among moms with autistic children who took Tylenol during pregnancy. 

The background here appear to be simply that RFK Jr promised to find the cause of autism by September 2025, and since we're nearing the end of Sept. 2025, RFK Jr had to deliver something. In his words, he claimed to have launched a "massive testing and research effort that's going to involve hundreds of scientists from around the world. By September, we will know what has caused the autism epidemic and we'll be able to eliminate those exposures." Trump suggested in response that this means RFK Jr will be able to produce medical advice that says if we "stop taking something, stop eating something or maybe it's  a shot.... but something's causing it." This announcement appears to be an attempt to fulfill that promise. Did it succeed?

1. The Announcement Reveals no New Research

As best as I can tell, we've heard nothing back from this "massive research effort," and nobody knows who these "scientists from around the world" are. There has been no report from this effort. The advice given appears to be based on advice dating back to a statement from Andrea Baccarelli, which was testimony from a lawsuit in 2023. He reviewed the scientific literature at the time and concluded that prenatal exposure to acetaminophen can cause neurodevelopmental disorders (NDDs) such as ASD and ADHD. Except a federal judge found that testimony to be "unreliable," and Harvard acknowledged that Baccarelli was paid ~$150,000 for working on that case. More recently, a more reliable meta-analysis published in August of this year co-authored by Baccarelli that evaluated 46 studies on the relationship between Tylenol and NDDs. Prada et al[1] found that:
27 studies reported positive associations (significant links to NDDs), 9 showed null associations (no significant link), and 4 indicated negative associations (protective effects). Higher-quality studies were more likely to show positive associations. Overall, the majority of the studies reported positive associations of prenatal acetaminophen use with ADHD, ASD, or NDDs in offspring, with risk-of-bias and strength-of-evidence ratings informing the overall synthesis.
But the paper does not conclude that acetaminophen definitely causes of ASD, only that it's a "potential" cause that is "plausible," and even the association "warrants caution" since "untreated maternal fever and pain pose risks such as neural tube defects and preterm birth."
While population-level trends in NDD rates have risen, potentially due to several factors including improved diagnostics and external exposures, further research is needed to confirm these associations and determine causality and mechanisms. A causal relationship is plausible because of the consistency of the results and appropriate control for bias in the large majority of the epidemiological studies, as well as acetaminophen’s biological effects on the developing fetus in experimental studies. Further, a potential causal relationship is consistent with temporal trends—as acetaminophen has become the recommended pain reliever for pregnant mothers, the rates of ADHD and ASD have increased > 20-fold over the past decades. 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.
Since this paper was a meta-analysis of studies already conducted and published in the literature, it cannot be the "massive testing and research effort" that RFK Jr alluded to. But clearly it should be acknowledged that the existence of an "association" and a "potential" cause does not mean that a definitive cause for ASD has been identified. This paper does not fulfill RFK Jr's promise that "we will know what has caused the autism epidemic and we'll be able to eliminate those exposures."

2. There is No Compelling Evidence of a Causal Link between Tylenol and ASD

The journal Nature has already weighed in on on this announcement. In evaluating the evidence for a causal link, they point to two important studies. One study in Sweden examined nearly 2.5 million pregnancies and found that the difference in ASD rates between pregnancies with and without acetaminophen use was very small.
The study led by Ahlqvist harnessed data on nearly 2.5 million children born in Sweden between 1995 and 2019 and — from the country’s extensive health records — data on acetaminophen prescriptions during pregnancy and on self-reported use collected by midwives, as well as whether children later received autism diagnoses.
The study showed that around 1.42% of children exposed to acetaminophen during pregnancy were autistic, compared to 1.33% of children who were not exposed ─ a “very small” difference, says Ahlqvist.
Ahlquvist's study[2] also controlled for confounding factors due to genetics by evaluating sibling pairs. They found a hazard ratio (HR) of "0.98 [95% CI, 0.93-1.04]." The HR statistic is helpful at assessing relative risk. A value that is greater than 1 indicates increased relative risk. A value less than 1 indicates lower relative risk. Ahlquvist's study found an HR in which the CI is small and overlaps 1, meaning that we cannot conclude that there is any increase in relative risk on the basis of this population-level analysis of nearly 2.5 million pregnancies.

The Nature article also highlights another high quality study in "Japan including over 200,000 children — also using sibling comparisons and published this year — found no link between acetaminophen use in pregnancy and autism." And that's correct. Okubo's analysis[3] found an HR of "1.06 (95% CI: 0.98, 1.15) for ASD." Since the CI range overlaps 1, there can be no conclusion that prenatal Tylenol use puts children at greater risk of ASD.

3. Studies With Contrasting Results

So what should we make of a meta-analysis showing an association with a "potential" causal link and multiple high powered studies with very large sample sizes that show no change in relative risk due to the prenatal use of Tylenol? Another meta-analysis by Damkier et al 2025[4] explains why some studies show a positive association between prenatal Tylenol use and ASD.
Most studies that have reported positive findings are difficult to interpret because they have important biases, notably a high degree of selection bias, variability in selection and adjustment for various potential confounders, and unmeasured familial confounding. When unobserved familial confounding through sibling analysis was controlled for, associations weakened substantially. This suggests that residual confounding from shared genetic and environmental factors may have caused an upward bias in the original observations. According to the current scientific evidence, in utero exposure to acetaminophen is unlikely to confer a clinically important increased risk of childhood ADHD or ASD.
This to me is extremely important. It seems clear that confounding factors prohibit making a strong case for a causal connection - factors such as taking Tylenol to treat an underlying health condition that might be an environmental factor associated with autism. It could be the causal relationship is between the underlying condition and autism, not between Tylenol and autism. When studies control for these factors, this removes what appears to be an upward bias in some observational studies. So if there is any relation between prenatal Tylenol use and ASD, it's likely very small and swamped by other more significant factors.

4. Tylenol Treats Conditions with a Stronger Link to Neurodevelopmental Disorders

It's well-documented that pain and high fevers during pregnancy do have links to negative health effects to their children, and Tylenol is often the only safe way to treat these conditions during pregnancy. So if you have a high fever, you're probably better off treating the fever with Tylenol. Certainly it's better to follow the medical advice of OBGYN doctors over the opinions of politicians that can't even pronounce acetaminophen. The American College of Obstetricians and Gynecologists (ACOG) currently advises the use of Tylenol to treat pain and fever during pregnancy.
Acetaminophen is one of the few options available to pregnant patients to treat pain and fever, which can be harmful to pregnant people when left untreated. Maternal fever, headaches as an early sign of preeclampsia, and pain are all managed with the therapeutic use of acetaminophen, making acetaminophen essential to the people who need it. The conditions people use acetaminophen to treat during pregnancy are far more dangerous than any theoretical risks and can create severe morbidity and mortality for the pregnant person and the fetus. When considering the use of medication in pregnancy, it’s important to consider all potential risks along with any benefits. The data from numerous studies have shown that acetaminophen plays an important—and safe—role in the well-being of pregnant women.
Similar advice is given by the Society for Maternal Fetal Medicine (SMFM). Of course, anything can change with continued research, but current advice from OBGYN doctors is that Tylenol is a safe way to treat pain and fever that can help limit risks of other complications like preeclampsia.

Conclusion

To my knowledge, no doctor would recommend taking any medication when it's not needed or at a higher dose than is medically advisable. So the advice from the current administration that pregnant mothers shouldn't take Tylenol if they don't need to or at a higher dose than necessary essentially just means, "continue as you are." Isn't this always the case with just about any medication? RFK Jr's advice changes nothing medically, but it likely will increase the level of fear and guilt among mothers, especially during pregnancy. Mothers with autistic children might needlessly feel like they made horrible mistakes when they took Tylenol when they were pregnant. I can't see any upside to this announcement in terms of a benefit to public health or identifying any new insights into the causes of autism and what exposure to limit to reduce the risk of autism. Here are links to some video shorts by medical doctors evaluating the same claims:
It's easy to create the impression of a causal link if you cherry pick a study that suggests results that are favorable to your desired outcome, then ignore the confounding variables that suggest strongly that it's premature to say there's a causal connection and no indication of a significantly increased relative risk. Given the current state of the evidence, I strongly suspect OBGYN doctors will not change the current standard of care to take Tylenol to treat fevers and pain during pregnancy. I suspect RFK Jr had to follow through on his promise to deliver something about ASD this month, and this is all he could come up with. But the announcement appears to be nothing more than fearmongering that will have the result of causing guilt trips for mothers on the basis of what appears to be no new evidence challenging what medical professionals already knew and understood.





References:

[1] Prada, D., Ritz, B., Bauer, A.Z. et al. Evaluation of the evidence on acetaminophen use and neurodevelopmental disorders using the Navigation Guide methodology. Environ Health 24, 56 (2025). https://doi.org/10.1186/s12940-025-01208-0

[2] Ahlqvist VH, Sjöqvist H, Dalman C, et al. Acetaminophen Use During Pregnancy and Children’s Risk of Autism, ADHD, and Intellectual Disability. JAMA. 2024;331(14):1205–1214. doi:10.1001/jama.2024.3172

[3] Okubo Y, Hayakawa I, Sugitate R, Nariai H. Maternal Acetaminophen Use and Offspring's Neurodevelopmental Outcome: A Nationwide Birth Cohort Study. Paediatr Perinat Epidemiol. 2025 Sep 2. doi: 10.1111/ppe.70071. Epub ahead of print. PMID: 40898607.

[4] Damkier P, Gram EB, Ceulemans M, Panchaud A, Cleary B, Chambers C, Weber-Schoendorfer C, Kennedy D, Hodson K, Grant KS, Diav-Citrin O, Običan SG, Shechtman S, Alwan S. Acetaminophen in Pregnancy and Attention-Deficit and Hyperactivity Disorder and Autism Spectrum Disorder. Obstet Gynecol. 2025 Feb 1;145(2):168-176. doi: 10.1097/AOG.0000000000005802. Epub 2024 Dec 5. PMID: 39637384.

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