Does Tylenol cause autism, what do the studies say?

Key Points

• Tylenol (acetaminophen), also known as paracetamol, is a common pain reliever and fever reducer. It is found over the counter alone and in combination with other medications.
• Numerous studies have reported a possible link between Tylenol use during pregnancy or after birth and autism spectrum disorder (ASD). However, most studies did not take genetics, indication, or environmental factors into account.
• Research on the association between Tylenol use and autism is mixed. Some studies have found a link between prenatal and postnatal use of acetaminophen and ASD, while others have not.
• More research is needed to understand the effects of Tylenol on babies when taken during pregnancy. There is currently not enough evidence to know if Tylenol causes autism.

The first study suggesting a possible link between Tylenol (acetaminophen) use during pregnancy and the risk of autism spectrum disorder was published in 2008. Since then, numerous studies have also identified a connection. Until now, there are no published randomized controlled trials – the gold standard for determining causal relationships.

Most studies did not take into account genetics, indications for Tylenol, or environmental factors. A more recent cohort study published in 2024 comparing siblings did not find an association between Tylenol use during pregnancy and the risk of autism.

Experts from trusted organizations around the world have concluded there is insufficient evidence to know if Tylenol causes ASD, but are cautioning women to only take Tylenol at the lowest dose for the shortest time possible and to weigh the risks and benefits with their healthcare provider.

Below we review studies looking at Tylenol use before and after birth and the risk of autism spectrum disorder.

What is autism spectrum disorder?

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that can be diagnosed at any age, but most commonly appears before age 2. According to the CDC, about 1 in 36 children have ASD.

Symptoms of ASD include communication difficulty, limited interests, and trouble in social situations. While there are some known genetic factors linked with ASD, other causes are not known. Other factors associated with ASD include maternal age, premature birth, vitamin deficiencies, environmental toxins, and inflammatory responses to infections.

Why might Tylenol cause autism?

It has not been proven that Tylenol causes autism, nor has a mechanism been fully elucidated. Still, some researchers have theories about how Tylenol might cause autism in some children.

One theory is that Tylenol may be neurotoxic in some babies. Some research suggests children with ASD metabolize Tylenol less well compared to children without ASD. It has also been observed that children with ASD have lower levels of the antioxidant glutathione, which is important for detoxifying byproducts of Tylenol such as N-acetyl-p-benzo-quinone-imine (NAPQI). This can make children more prone to Tylenol toxicity which can affect the brain.

Another theory is that Tylenol may trigger the endocannabinoid system, which interferes with normal immune system development. Several studies have shown that children with ASD have immune system problems. More research in this area is needed.

Studies on Tylenol and autism

Studies looking at the connection between autism and Tylenol have mixed conclusions. Some have found a possible link between prenatal or postnatal use of Tylenol and ASD, while others found no connection.

Study 1

One of the earliest studies suggesting a link between Tylenol and ASD was published in 2008 in Autism: the international journal of research and practice. The study was a case-control study that examined results of an online parental survey. It included 83 children with ASD and 80 children without ASD. The study found that children who took Tylenol after MMR vaccination were more likely to have ASD compared to children who did not take it.

Study 2

In a large 2016 cohort study, researchers followed around 64,000 children in the Danish National Birth Cohort for about 13 years. After conducting phone interviews, they found that about 50% of women used Tylenol during pregnancy. They also found that women who used Tylenol during pregnancy were associated with a higher risk of a certain type of ASD (accompanied by hyperkinetic symptoms) in their children, but not with other types of ASD.

Study 3

A 2016 study reviewed data from the National Database for Autism Research of the National Institute of Mental Health. Only children without known genetic conditions linked to ASD were included. Data from 118 children with ASD and 79 control children were reviewed. Researchers found that the use of Tylenol in children with ASD was different compared to children without ASD.

Study 4

A 2016 study examined the use of Tylenol during pregnancy in 2,644 mother-child pairs and the effects on neurodevelopment outcomes in children at ages 1 to 5 years old. Researchers found that use of Tylenol during pregnancy was associated with a higher number of ASD symptoms in males.

Study 5

In a 2018 systematic review and meta-analysis, researchers included seven studies involving over 132,000 pairs of mothers and children. They were followed for 3-11 years. Exposure to Tylenol was assessed through interviews and questionnaires. Researchers found that exposure to Tylenol during pregnancy increased the risk of ASD by 20%.

It is noted that the evidence reviewed was observational and susceptible to potential confounding factors. For example, fevers and infections during pregnancy have also been linked with ASD. Additionally, most studies included did not report what other medications pregnant women were taking.

Study 6

A 2020 study that included survey data from parents of 1,515 children looked at Tylenol use before the age of two in males. Researchers found that Tylenol use before age 2 was associated with ASD in male children. The study was not able to obtain information about doses of Tylenol that were used.

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Study 7

A 2020 study examined the association between cord plasma biomarkers of Tylenol exposure and the risk of ASD in children. The cohort study included almost 1,000 mother and children pairs from the Boston Birth Cohort. Biomarkers examined included metabolites of Tylenol. Researchers found an association between cord biomarkers of Tylenol exposure during pregnancy and ASD. Babies with biomarkers present were about three times more likely to be diagnosed with ASD.

Limitations of the study are that they only included a one-time measurement of Tylenol biomarkers when babies were born, which likely reflects the mother’s use shortly before birth. They were also not able to capture all metabolites of Tylenol. Additionally, researchers did not include other genetic or environmental factors in the analysis.

Study 8

A 2021 meta-analysis in six European population-based cohorts included around 74,000 mother-child pairs. Researchers assessed prenatal and postnatal (up to 18 months) Tylenol exposure through interviews and questionnaires. ASD symptoms were assessed at 4 to 12 years old. The study found that children were at around a 20% higher risk for ASD symptoms if they were exposed to Tylenol while in the womb compared to children who were not exposed. Children exposed to Tylenol after birth were not associated with a higher risk of ASD symptoms.

Study 9

A 2022 systematic review of the link between ASD and Tylenol included 16 studies. They found that all studies showed an association between Tylenol use and poor neurodevelopmental outcomes. They also found that long-term use, higher doses, and more frequent use raised the risk even higher. Developmental disabilities were more common in boys compared to girls, except for ADHD where girls and boys were affected equally. Researchers concluded that pregnant women should use Tylenol in a limited way until more research is done.

Study 10

In 2024, a cohort study in Sweden included about 2.5 million children born between 1995 and 2019. Researchers examined the use of Tylenol during pregnancy from records. They found that without sibling control, the use of Tylenol during pregnancy was marginally associated with a higher risk of autism. However, when sibling pairs were analyzed, there was no evidence of Tylenol use during pregnancy raising the risk of autism or other intellectual disability.

To explain the previous research published in medical literature, researchers concluded that previous findings may have been due to familial confounding. Because siblings share genetics and typically grow up in similar environments, sibling studies are thought to be more accurate and have a smaller risk of external factors skewing the results.

What do the experts say on the link between Tylenol and autism?

Despite some evidence of an association between Tylenol and autism, experts continue to recommend the medication to treat pain and fever during pregnancy. They caution to use the smallest amount and for the shortest time necessary.

Consensus Statement Published in Nature Reviews Endocrinology

In 2021, a group of scientists, medical experts, and public health professionals published a consensus statement on the use of Tylenol during pregnancy. They cautioned that a growing body of research suggests Tylenol use during pregnancy might alter fetal development and could raise the risks of brain and reproductive problems. They also recommended pregnant women should not use Tylenol unless medically necessary, and to always consult with their healthcare provider if they are unsure or before using long-term.

The American College of Obstetricians and Gynecologists

In 2021, the American College of Obstetricians and Gynecologists (ACOG) published a response to a consensus statement claiming Tylenol use during pregnancy can negatively affect fetal development. They stated that studies conducted on the association between Tylenol use during pregnancy and developmental issues show no clear evidence nor do they prove a direct relationship between the two. It is also noted that the brain continues developing until at least 15 months old, which leaves room for many different exposures.

The ACOG recommended no change in clinical practice until more definitive research is done. Patients were encouraged to only use medications as needed during pregnancy, and to always consult with their healthcare provider first.

European Medicines Agency

In 2021, the European Medicines Agency (EMA) reviewed evidence from literature on the impact of Tylenol use during pregnancy on neurodevelopment. They concluded epidemiological studies on neurodevelopment in babies exposed to Tylenol during pregnancy were inconclusive. The EMA also stated that Tylenol can be used during pregnancy, but at the lowest effective dose for the shortest time and frequency possible.

U.S. Food and Drug Administration

In 2015, the U.S. Food and Drug Administration (FDA) published a Drug Safety Communication about the potential risks of using pain medication during pregnancy. After reviewing studies, the FDA determined they were too limited to make any recommendations. Only one study involving Tylenol was included in their review, which researched the risk of ADHD with Tylenol use during pregnancy – not autism.

In the public communication, the FDA urged people to use caution when taking pain medications during pregnancy, and to discuss all medications with their healthcare provider. They also noted that pain can lead to undesirable outcomes for the mother and baby if left untreated, and the risks and benefits should be weighed before using prescription or OTC pain medications during pregnancy.

This is not all the information you need to know about Tylenol (acetaminophen) for safe and effective use and does not take the place of your doctor’s directions. Review the full product information and discuss this information and any questions you have with your doctor or other health care provider.