The Science Behind Tylenol Use During Pregnancy and Autism

The Science Behind Tylenol Use During Pregnancy and Autism

Mothers and families across the U.S. are filing lawsuits against Tylenol and other acetaminophen manufacturers, alleging that taking the drug during pregnancy resulted in their child having autism or ADHD. Below we reference studies and data that the makers of Tylenol and other manufacturers have been aware of for a long time.

  • How exactly acetaminophen affects a developing baby's brain.
  • Studies that support this information going back almost 25 years.
  • Criticism and common misconceptions about the link between Tylenol and autism.
  • How much Tylenol during pregnancy is safe? What the experts say.
  • New proposed warning label for acetaminophen bottles.
  • How the lawsuit is moving forward and how you can join.

Over the past year, families of children diagnosed with autism spectrum disorder have filed Tylenol lawsuits against the maker of Tylenol, Johnson & Johnson, and manufacturers of generic acetaminophen painkillers. These lawsuits have raised similar allegations that pregnant women were not adequately warned that Tylenol may cause autism in their unborn babies.

These so-called ‘Tylenol Autism Lawsuits’ lawsuits point to more than two dozen different credible peer-reviewed studies that suggest acetaminophen in Tylenol increases the risk of an unborn child developing autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and possibly other developmental complications.

Because of the sheer number of cases filed, the U.S. Judicial Panel on Multidistrict Litigation decided to centralize and consolidate the litigation before U.S. District Judge Denise Cote in October 2022. This helps to avoid duplicate discovery and conflicting rulings from different courts and makes it easier on plaintiffs.

Early in the pretrial proceedings, Judge Cote rejected attempts by the drug manufacturers to dismiss the litigation, and in August the court denied a request to allow Johnson & Johnson to pursue an immediate appeal of the rulings

So despite their best efforts, the discovery phase of the lawsuit into the link between Tylenol and autism is set to move forward. During this time, the size and scope of the litigation are expected to increase dramatically, as more families realize that there may be a connection between Tylenol and their child’s autism spectrum disorder diagnosis.

In this post, Lawsuit Legal News will explore the current evidence linking a child’s risk of autism spectrum disorder to acetaminophen exposure during pregnancy, and outline scientific studies and reports being used to support allegations. We will also break down the mechanics of how Tylenol potentially causes autism in the developing fetus.

What Are the Mechanics Behind How Tylenol Can Cause Autism?

Independent research and scientific studies have identified several mechanisms in the body that may explain how Tylenol may cause autism when used during pregnancy.

While many families initially believe that autism is caused by genetic factors, there is evidence that acetaminophen may have an impact on the brain of a developing fetus, resulting in a number of side effects that may cause autism, including:

1. Hormonal Disruption

Acetaminophen has been shown to influence hormone levels, such as reducing testosterone production, which may play a role in brain development and the risk of neurodevelopmental disorders like autism.

2. Oxidative Stress

Acetaminophen is metabolized in the liver, leading to the production of reactive oxygen species (ROS) and oxidative stress. Excessive oxidative stress during critical periods of fetal brain development could potentially disrupt normal neural development and cause children to develop autism and other developmental disorders.

3. Glutathione Depletion

Acetaminophen has been shown to deplete levels of glutathione, an essential antioxidant in the body. Glutathione plays a crucial role in protecting cells, including neurons, from oxidative damage. Reduced glutathione levels may lead to increased vulnerability to oxidative stress and potential neurodevelopmental disorders, such as autism or ADHD.

4. Immune System Modulation

Acetaminophen may influence immune responses, including inflammation and immune system regulation. Alterations in immune function during pregnancy could potentially impact child development and put unborn children at higher risk of developing neurodevelopmental disorders.

diagram showing embryo development as reference to info about a baby's developing brain from tylenol

Looking at the Studies: Acetaminophen Exposure Linked to Autism

Researchers have examined the association between Tylenol use during pregnancy and the risk of autism through observational studies and epidemiological research since it is unethical to conduct studies on pregnant women.

Here are some key findings from the studies:

Study 1: Scientists Say Acetaminophen Most Harmful at Beginning of Trimester

Serious concerns about acetaminophen use during pregnancy were raised by 91 scientists and public health professionals in a Consensus Statement published in Nature Reviews Endocrinology in September 2021.

The group of scientists formed their Consensus Statement after reviewing 29 studies on acetaminophen exposure and adverse neurodevelopmental outcomes, which involved more than 220,000 mother-child pairs across the globe.

Of the 29 studies, 26 indicated that prenatal exposure to acetaminophen, as well as perinatal use or exposure, negatively impacts fetal brain development, increasing a child’s risk of autism or ADHD diagnosis.

Scientists specifically stated the most detrimental effects of long-term use and exposure to acetaminophen for children were found at the beginning of the third trimester and around the time of birth.

Given the mounting human scientific evidence supporting Tylenol’s link to autism, the authors urged the FDA and EMA, as well as obstetric and gynecological societies, to review all available data and provide an evidence-based evaluation of risk to inform pregnant women and their healthcare professionals.

The statement further recommended warning labels should be included on acetaminophen packaging while additional research and risk evaluations are performed.

Study 2: Children Exposed to Acetaminophen During Pregnancy Linked to Higher Rates of Autism

In a study published in the European Journal of Epidemiology in May 2021, researchers analyzed data from 73,881 children and found a clear link between prenatal acetaminophen exposure and an increased risk for autism and ADHD diagnoses.

Results showed that children exposed to acetaminophen while in the womb are 19% more likely to have Autism symptoms when compared to children who were not exposed to acetaminophen during pregnancy.

To further reinforce the risk of infant exposure to acetaminophen during pregnancy, the study did not find any association between postnatal exposure to acetaminophen and autism.

Study 3: Pregnant Women With Acetaminophen in Cord Blood Samples Birthed Children with Higher Autism Rates

In a study published in JAMA Psychiatry in October 2019, researchers looked at 996 mother-infant pairs to determine whether the amount of acetaminophen found in umbilical cord blood samples increased the rate of both autism spectrum disorder and attention deficit hyperactivity disorder (ADHD).

Researchers found the chances of an autism spectrum disorder diagnosis increased significantly when higher levels of acetaminophen were found in umbilical cord blood samples.

Specifically, the children with the highest level of acetaminophen in umbilical cord blood samples were at a 262% increased risk of Autism spectrum disorder diagnosis when compared to the lowest level.

Study 4: Single Use of Acetaminophen During Pregnancy Increased Autism Risks by 41%

According to a study published in the International Journal of Epidemiology in 2016, researchers found that among 2,644 mother-child pairs recruited during pregnancy, even a single use of acetaminophen during pregnancy increased the risk of autism by 41%.

Researchers further found that frequent use of acetaminophen pain relief drugs more than doubled the risk of hyperactivity and impulse disorders, like ADHD. Additionally, researchers indicated the frequent use of acetaminophen negatively impacted fetal development and increased the overall chances of a child developing a complex developmental disorder.

Study 5: Acetaminophen Use During Early Pregnancy Increases Child’s Risk Of Autism and Hyperactivity Symptoms

A study published in the International Society for Autism Research in 2015, found that prenatal use of acetaminophen was associated with an increased risk of autism spectrum disorder, accompanied by hyperactivity symptoms.

Researchers collected data from the Danish National Birth Cohort study, which followed 64,322 children and mothers for an average of 12.7 years. According to the findings, researchers identified prenatal use of acetaminophen increased the risk of autism spectrum disorder with hyperactivity symptoms by 51%. The risk was higher with prolonged use of 20 or more weeks.

The findings of this study suggest that acetaminophen exposure early in fetal life may specifically impact hyperactive behavioral phenotypes. The authors concluded that in-utero exposure to acetaminophen could lead to neurodevelopmental injuries, including ASD, and urged pregnant women to consider alternatives for managing pain and fever.

Study 6: Fetal Exposure to Acetaminophen Impacts Brain Development in Mice

Since human trials are not ethical or legal, researchers have explored the use of acetaminophen in mice to determine whether exposing mice in utero to acetaminophen caused newborn mice to develop Autism.

In a study published in the journal Frontiers in Toxicology, researchers found that mice who were neonatally exposed to acetaminophen showed altered and spontaneous behavior, reduced memory, and both learning and cognitive challenges compared to mice born without exposure to acetaminophen.

In the study on mice, researchers further sought to understand how acetaminophen altered the developing brain. The study indicated that after neonatal mice were exposed to acetaminophen, an increase in markers for oxidative stress was identified in the part of the brain that is responsible for emotion, memory, and the autonomic nervous system.

The authors stated that even at low doses, such persistent and negative effects on a developing brain could cause the risk of brain damage.

Study 7: Early Findings on the Relationship Between Tylenol and Neurodevelopmental Disorders

The Yale University School of Public Health's findings, backed by 91 scientists in a consensus statement, were among the first to highlight the harmful effects of acetaminophen use during pregnancy on fetal brain development, according to Dr. Zeyan Liew of Yale.

The statement's authors based their conclusions on twenty-five years of epidemiological, animal, and in-vitro studies. These studies showed a connection between Tylenol and increased risks of disorders like autism spectrum disorder, attention deficit hyperactivity disorder, decreased IQ, and language delays.

It's important to mention that acetaminophen can cross the placental barrier. This may lead to changes in maternal hormones and negative impacts on fetal development.

Study 8: 2022 Study on Acetaminophen's Connection to Neurodevelopmental Injuries

A recent study from October 2022 (still under peer review) titled "Acetaminophen Causes Neurodevelopmental Injury in Susceptible Babies and Children: No Valid Rationale for Controversy" examines the association between Tylenol use during pregnancy and neurodevelopmental injuries. This research stands out as it evaluates confounding factors within the context of all previous related studies.

Toddler playing with toys showing tactile skills

Some critics argue that the rise in autism diagnoses is due to improved criteria and awareness, rather than acetaminophen exposure. They also mention that correlation doesn't imply causation. As we have mentioned, ethical concerns prevent the direct study of potentially harmful substances on pregnant women, making research dependent on observational data.

However, animal studies have consistently shown that acetaminophen hinders fetal brain development. It's worth noting that these animals weren't consuming acetaminophen for medical reasons. Every research on pregnant women has indicated a positive link between acetaminophen use and autism.

After examining various factors and criticisms, we believe there's a valid reason to connect in-utero acetaminophen exposure to neurodevelopmental injuries, including autism. And the courts seem to agree. This is further supported by evidence showing increased oxidative stress, which is linked to such injuries.

It's crucial to clarify that we're not asserting that Tylenol directly causes autism. It seems to be a contributing factor, not the sole cause.

Is Tylenol Safe to Take During Pregnancy?

Moderate use of Tylenol during pregnancy has been considered safe for decades, and most doctors continue to indicate pregnant women can take the pain medication on occasion. 

However, lawsuits point to a number of studies that have warned that the risk of unborn children developing autism spectrum disorder may vary greatly, depending on the amount of acetaminophen used, and what trimester of the pregnancy the pain medication is taken.

How Much Tylenol is Safe to Take While Pregnant?

Johnson & Johnson and other drug makers have not provided adequate information about the amount of Tylenol that is safe for pregnant women to take, according to Matthew Dolman.

“That is one of the biggest problems here. How are women supposed to know how much Tylenol is safe to take while pregnant and what the risks are, especially if the manufacturer doesn't even have to mention it on the bottle.”

As a result, most pregnant women follow the standard warnings not to exceed the maximum recommended dose of 4,000 milligrams of acetaminophen daily, since there are no specific warnings about the potential autism risk when Tylenol is regularly and routinely taken while pregnant.

Many of the mothers of children diagnosed with autism after using Tylenol during pregnancy report that they routinely used the pain medication 3 to 6 times per week, often throughout the entire course of their pregnancy.

Families pursuing lawsuits say that they never would have taken the pain medication as frequently if they had been aware of the potential autism risk, and indicate that the Tylenol warning label should have made it clear that pregnant women should use the lowest effective dose for the shortest possible frequency to treat pain or fever.

Proposal for Acetaminophen Autism Warning Label

During the pretrial proceedings, lawyers for the plaintiffs submitted an example of an acetaminophen pregnancy warning label that could be added to Tylenol.

The example labels suggest that warnings could look something like:

Autism/ADHD: Some studies show that frequent use of this product during pregnancy may increase your child’s risk of autism and attention deficit hyperactivity disorder. If you use this product during pregnancy to treat your pain and/or fever, use the lowest effective dose for the shortest possible time and at the lowest possible frequency.

Woman looking at warning label on medicine bottle in a pharmacy

Tylenol Autism Lawsuits Cleared to Move Forward with Discovery

As of August 2023, there are currently 266 autism and ADHD lawsuits pending in the Tylenol multidistrict litigation.

Johnson & Johnson and other defendants filed motions to dismiss the claims shortly after the MDL was established, arguing that they should be shielded from failure to warn lawsuits under a legal defense known as federal preemption. The drug makers argued that federal rules circulated by the FDA, which regulate how over-the-counter medications are manufactured and marketed in the U.S., should preempt the state-law-based failure to warn claims.

But as we have mentioned, Judge Cote has rejected Johnson and Johnson’s argument, finding that the Tylenol autism lawsuits are not preempted.

As a result, the litigation is moving forward.

Read more about the latest Tylenol lawsuit updates.

Have a Tylenol Lawsuit Lawyer Review Your Potential Case

It is important to obtain experienced legal representation to pursue a Tylenol autism lawsuit or Tylenol ADHD lawsuit so that you can protect your legal interests and make sure your family receives the financial compensation they deserve.

A Tylenol Lawsuit Lawyer will provide a free consultation to help determine if you or a loved one may be eligible to file a claim. There are no fees or expenses unless a recovery is obtained in your case.


Matthew Dolman

Personal Injury Lawyer

This article was written and reviewed by Matthew Dolman. Matt has been a practicing civil trial, personal injury, products liability, and mass tort lawyer since 2004. He has represented over 11,000 injury victims and has served as lead counsel in over 1000 lawsuits. Matt is a lifetime member of the Million Dollar Advocates Forum and Multi-Million Dollar Advocates Forum for resolving individual cases in excess of $1 million and $2 million, respectively. He has also been selected by his colleagues as a Florida Superlawyer and as a member of Florida’s Legal Elite on multiple occasions. Further, Matt has been quoted in the media numerous times and is a sought-after speaker on a variety of legal issues and topics.

Learn More

Latest News