Response to: link between Tylenol & autism?

Claims have been made about a causal link between Tylenol and autism. Is there truth to that? I reviewed the research on why they’re associated and what actually increases the likelihood of having an autistic child (hint: it’s not Tylenol).

TL;DR:

• Tylenol is still the safest option for treating fevers during pregnancy, according to the leading experts. By avoiding treating the fever, you put your child at risk, and other challenges can arise.
• Research shows that a fever during pregnancy can activate autistic genes. Though autistic genes are not problematic in themselves, an untreated fever raises a number of concerns including learning disabilities, neurodevelopmental disorders, intellectual disability, and high support needs. It seems that the higher the fever and longer the duration, the more damage it does.

Acetaminophen (Tylenol): Acetaminophen is the generic name, while Tylenol is the brand name most people are familiar with.

Tylenol (acetaminophen) & autism

I want to take a moment to acknowledge the distress in the autism community after recent statements linking Tylenol (acetaminophen) use during pregnancy to autism. For autistic adults, parents, and loved ones alike, these kinds of claims are painful. They suggest that autism is a preventable mistake, the result of something a mother did, and that narrative is scientifically misleading and stigmatizing. Autism is broad and diverse. Some of us require daily care, while others live independently and thrive in their careers and relationships.

Fevers in pregnancy increase risks for many different complications, so it’s essential to treat them safely. Treating fever isn’t about preventing autistic people from existing; it’s about protecting the health of both parent and baby in all respects.^[1]Systematic review and meta-analyses: Fever in pregnancy and health impacts in the offspring (Dreier et al., 2014)^[2]Fever during pregnancy and risk of neurodevelopmental disorders in offspring: A systematic review and meta-analysis (Antoun et al., 2021)

Fever has multiple risks. It is associated with miscarriage, premature birth, neural tube defects, congenital heart problems, autism and preterm labour.^[3]Maternal hyperthermia and the risk for neural tube defects in offspring: Systematic review and meta-analysis (Moretti et al., 2005)^[4]Periconceptional maternal fever, folic acid intake, and the risk for neural tube defects. (Kerr et al., 2017)^[5]Maternal fever during pregnancy and risk of congenital heart diseases in offspring: A meta-analysis (Shi et al., 2014)^[6]Prenatal fever and autism risk (Hornig et al., 2018)^[7]Infection and fever in pregnancy and autism spectrum disorders: Findings from the Study to Explore Early Development (Croen et al., 2019) The primary reason for treating fever is to ensure overall maternal and fetal health.

Timing during pregnancy

First trimester (especially weeks 3–8):

High fevers during neural tube development are associated with an increased risk of neural tube defects and congenital heart defects.^[8]Maternal hyperthermia and the risk for neural tube defects in offspring: Systematic review and meta-analysis (Moretti et al., 2005)^[9]Maternal hyperthermia and the risk for neural tube defects in offspring: Systematic review and meta-analysis (Moretti et al., 2005)^[10]Periconceptional maternal fever, folic acid intake, and the risk for neural tube defects. (Kerr et al., 2017)^[11]Maternal fever during pregnancy and risk of congenital heart diseases in offspring: A meta-analysis (Shi et al., 2014)

A sustained fever ≥39 °C (102.2 °F) can raise the risk of neural tube defects if folate intake is low.^[12]Maternal hyperthermia and the risk for neural tube defects in offspring: Systematic review and meta-analysis (Moretti et al., 2005)^[13]Periconceptional maternal fever, folic acid intake, and the risk for neural tube defects. (Kerr et al., 2017)

Second trimester:

Fevers during this trimester are most strongly linked to later increase in the probability of autism.^[14]Infection and fever in pregnancy and autism spectrum disorders: Findings from the Study to Explore Early Development (Croen et al., 2019)^[15]Prenatal fever and autism risk (Hornig et al., 2018) The Kaiser Permanente study found a 2.1× increase in autism predisposition from 2nd-trimester fevers.^[16]Infection and fever in pregnancy and autism spectrum disorders: Findings from the Study to Explore Early Development (Croen et al., 2019)

Third trimester:

Risks are lower for structural defects, but fever can still trigger complications like preterm labour.^[17]Systematic review and meta-analyses: Fever in pregnancy and health impacts in the offspring (Dreier et al., 2014)

The science, when read carefully, tells a very different story from what’s being claimed. Associations between acetaminophen and autism are extremely small and appear to be due to confounding factors such as fever and infection when more rigorous sibling studies are conducted.^[18]Acetaminophen use during pregnancy and children’s risk of autism, ADHD, and intellectual disability. (Ahlqvist et al., 2024) Fever itself is associated with increased probability of autism in the child, which is why acetaminophen is still the recommended treatment for fever in pregnant people.^[19]Acetaminophen use in pregnancy and neurodevelopmental outcomes (Practice Advisory/FAQ) (ACOG, 2025)^[20]Maternal hospitalization with infection during pregnancy and risk of autism spectrum disorders^[21]Maternal infection during pregnancy and likelihood of autism and intellectual disability in children in Sweden: A negative-control and sibling comparison cohort study (Brynge et al., 2022) Maternal infection in pregnancy was more often linked with autism with intellectual disability, rather than without. This study hints that inflammatory processes (including fever) may contribute more to outcomes where there are broader neurodevelopmental impacts.

But let’s remember:

• Plausibility ≠ proof. It just means “we can see how this might happen in theory.”
• Human evidence is still indirect, mixed, and confounded (by genetics, environment, underlying infection, etc.).
• What we have is a logical, evidence-based mechanism that could explain the link between fever severity and the level of autism support needed. Still, the human data doesn’t yet establish causation.
• Fever → maternal immune activation → cytokine (inflammatory agents) release (e.g., IL-6, IL-17).
• Animal models have linked greater inflammation to more severe social and cognitive outcomes in offspring.^[22]Prenatal fever and autism risk (Hornig et al., 2018)
• Fevers (especially prolonged or multiple) may skew risk toward autism with higher support needs, but human evidence remains indirect and inconclusive.^[23]Maternal infection during pregnancy and likelihood of autism and intellectual disability in children in Sweden: A negative-control and sibling comparison cohort study (Brynge et al., 2022)

At the same time, I want to acknowledge the many parents in our community raising autistic children with significant support needs. For you, hearing these claims may evoke genuine fears and questions. Could I have done something differently? Please know: your choices did not cause your child’s autism.

What the research shows

The claim

Some public figures have suggested that using acetaminophen (Tylenol) during pregnancy increases the odds of autism in children and advise pregnant women to “fight like hell not to take it.”

The research

Acetaminophen

• Observational studies (e.g., meta-analyses, cohort studies) report small statistical associations between prenatal acetaminophen exposure and neurodevelopmental disorders (autism, ADHD).
• Effect sizes are small: in a Swedish cohort of ~2.48 million children, the absolute risk increase for autism was +0.09% (~1 extra case per 1,100 births).^[24]Acetaminophen use during pregnancy and children’s risk of autism, ADHD, and intellectual disability. (Ahlqvist et al., 2024)
• Gold-standard sibling studies (controlling for family/genetic factors) found no increased risk, suggesting earlier associations are largely due to confounding factors.^[25]Acetaminophen use during pregnancy and children’s risk of autism, ADHD, and intellectual disability. (Ahlqvist et al., 2024)
• Clinical guidance: The American College of Obstetricians and Gynecologists still recommends acetaminophen as the safest pain/fever treatment in pregnancy, used judiciously.^[26]Acetaminophen use in pregnancy and neurodevelopmental outcomes (Practice Advisory/FAQ) (ACOG, 2025)

Fever

Fever itself is a well-established “risk factor” for autism.

According to Kaiser Permanente cohort:^[27]Prenatal fever and autism risk (Hornig et al., 2018)^[28]Prenatal fever and autism risk (Hornig et al., 2018)^[29]Infection and fever in pregnancy and autism spectrum disorders: Findings from the Study to Explore Early Development (Croen et al., 2019)

• Fever in the second trimester → 2.12× risk of autism.
• Translates to ~5.3% risk vs. 2.5% baseline → about 28 extra cases per 1,000 births.

Norwegian Mother and Child Cohort:^[30]Prenatal fever and autism risk (Hornig et al., 2018)

• Single fever episode ~2× risk.
• Multiple fever episodes ~3× risk → up to 50 extra cases per 1,000 births.

Fever & odds of autism

• Croen et al found a 2.1× increase in the odds of autism after second-trimester fevers, but did not stratify by severity or support-needs profiles. Autism was treated as a single outcome.^[31]Infection and fever in pregnancy and autism spectrum disorders: Findings from the Study to Explore Early Development (Croen et al., 2019)
• Atladottir et al reported risk increases with multiple febrile episodes, but again, the autism diagnosis was not broken down into subtypes or severity.^[32]Autism after infection, febrile episodes, and antibiotic use during pregnancy: an exploratory study. (2012)
• Antoun et al did a systematic review & meta-analysis: Most combine all autism presentations together, since the DSM-5 no longer distinguishes subtypes.^[33]Fever during pregnancy and risk of neurodevelopmental disorders in offspring: A systematic review and meta-analysis (Antoun et al., 2021)
• Hornig et al. examined trimester-specific maternal fevers; second-trimester fever was associated with an increased predisposition to autism. Like others, autism was analyzed as a unitary outcome without severity stratification.^[34]Prenatal fever and autism risk (Hornig et al., 2017)
• Love et al did a large review and meta-analysis across prenatal environmental risk factors. They found fever during pregnancy associated with ~2.1× increased odds of autism. Again, all autism outcomes were aggregated.^[35]Prenatal environmental risk factors for autism spectrum disorder: An umbrella review (Love et al., 2024)

Fever severity & impacts

• Some studies have tried to parse whether prenatal infection or fever is more strongly associated with autism + intellectual disability.
• A Swedish registry study suggested maternal infection in pregnancy was more often linked with autism with intellectual disability, rather than without.^[36]Maternal hospitalization with infection during pregnancy and risk of autism spectrum disorders (Lee et al., 2015)^[37]Maternal infection during pregnancy and likelihood of autism and intellectual disability in children in Sweden: A negative-control and sibling comparison cohort study (Brynge et al., 2022)

This research hints that inflammatory processes (including fever) may contribute more to outcomes where there are broader neurodevelopmental impacts. However, this is not consistent across all studies—many find no clear differentiation.

What we can say right now

• Clear: Fever during pregnancy raises the overall likelihood of an autism diagnosis.
• Less clear: Whether this risk applies equally across the spectrum, or more to autistic people with intellectual disability / higher support needs.
• Emerging evidence: Some registry studies lean toward a stronger link with autism + ID, but not definitively.

Acetaminophen & fever vs. autism odds

Bottom line

• Acetaminophen: Any link with autism is extremely small and most likely explained by other factors—like the illness that caused the fever in the first place, genetics, overall health.
• Fever: Stronger and repeated evidence shows that untreated fever during pregnancy can raise the risk of autism.
• Clinical practice: According to current scientific evidence and medical guidelines, treating fever with acetaminophen is still considered the safest option for protecting both mother and child.

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