Due to class action lawsuits that have been filed, there is tremendous interest, especially by parents, in the relationship of autism and Tylenol. We are not lawyers and have no opinion on lawsuits.

That noted, we are experts at treating autism and other developmental delays in children and adults. So, as an aid to parents and other autism therapy professionals, we have developed this guide to understanding the ongoing published peer-reviewed research on autism and Tylenol. We will continuously update this autism and Tylenol research guide as further studies are published.

What is Tylenol?

Tylenol is a brand name for the drug commonly known as acetaminophen in the United States and Canada and known as paracetamol in the rest of the world. Chemically, it is N-acetyl-p-aminophenol and is sometimes referred to in academic journals as APAP. The name Tylenol comes from its chemical name (aceTYL-p-aminophENOL).

Autism and Tylenol

Back in 1884 Germany, two physicians used acetanilide, a derivative of aniline, a compound that had been isolated from coal tar and used in the production of the novel synthetic dyes that were all the rage, to treat a patient with a raging fever and intestinal worms. Acetanilide did nothing for the worms but did reduce the fever. They began marketing acetanilide as Antifebrin (medical-speak for anti-fever).

They would soon learn acetanilide’s nasty methemoglobinemia side-effect when the skin color of users turned a blueish color because of its inhibition of oxygen transport by hemoglobin. This led to a search for a way to make acetanilide safer by modifying its molecular structure to remove this nasty side-effect.

In 1887, the German pharmaceutical company Bayer did just that, producing phenacetin. That same year a Johns Hopkins chemistry professor, Harmon Morse, synthesized acetaminophen, which accomplished the same thing, but physicians at the time wrongly reported that it could sometimes still produce that nasty methemoglobinemia side-effect. Consequently, acetaminophen was shelved until 1947 when it was discovered that both acetanilide and phenacetin actually convert to acetaminophen in the body and that acetaminophen is the active fever-reducing compound in both drugs.

About Autism and Floortime Therapy

When a parent or caregiver hears the words “Your child has autistic spectrum disorder” from a psychologist or physician, it can often sound to that parent or caregiver like a life sentence. They believe that their child will always be autistic. That autism diagnosis, however, is dynamic not static.

What does it mean that your child’s diagnosis is dynamic? It means that it can change. Dr. Stanley Greenspan says that an autism diagnosis is dynamic. Floortime therapy can help in the development of children with autism spectrum disorder diagnoses.

There were three key developments in Dr. Greenspan’s research on children with autism and other developmental issues. The first of these is the importance of affect and relationships for the growth of the brain and mind. The second is the recognition that there are significant variations in the underlying processing capacities of children. The third is the recognition of what the integrated early stages of development actually are. You can learn more about Floortime therapy at our introduction to Floortime.

Associating Tylenol with Safety for Children and Pregnant Moms

Whereas Floortime is an autism treatment for children after they are born, the autism and Tylenol connection happens before the child is born. Why is this? This connection happens because for many years, and unlike aspirin and ibuprofen, Tylenol, including generic forms of acetaminophen or paracetamol, was considered a safe pain killer and fever reducer during pregnancy. After all, around 20% of the adult American population uses products containing Tylenol each week.

Tylenol has been considered the safest over-the-counter option for pregnant mothers. For years, its use within the recommended dosage was not thought to be harmful to developing in utero children. That view has more recently begun to change. Nevertheless, Tylenol and its generic formulations are among the most commonly used medications during pregnancy across the planet.

Why does acetaminophen have such a strong association with safety compared to other analgesics? Recall that phenacetin, discussed in the ‘What Is Tylenol?’ section above, was used instead of acetaminophen during the first half of the twentieth century. Phenacetin was eventually found to be associated with developing kidney problems. Another alternative, aspirin, was associated with stomach irritation and with Reye’s syndrome, a rare but serious children’s disease.

In the Spring of 1955, McNeil Laboratories launched TYLENOL Elixir for Children with acetaminophen as the active ingredient. McNeil Laboratories marketed Tylenol to physicians as a prescription-only safer alternative to aspirin and phenacetin. Their marketing campaign was wildly successful. The global acetaminophen market is now worth about $9.5 billion. In America, it’s estimated that about 65% of pregnant women use acetaminophen. It is the most commonly used over-the-counter medicine used during pregnancy.

Autism and Tylenol Research

This widespread commonality of Tylenol usage across the globe shapes our understanding of research findings about autism and Tylenol. It means that because Tylenol (acetaminophen or paracetamol) is used so much during pregnancy, even a small effect size on autism from using Tylenol will have significant effects on autism rates globally.

Autism and Tylenol Research Study 1: Paracetamol use during pregnancy–a call for Precautionary Action

We will begin with the 2021 Consensus Statement “Paracetamol use during pregnancy–a call for precautionary action” published in the prestigious scientific journal Nature Reviews Endocrinology. Unlike the other papers, this is not primary or scholarly medical research. This is a set of recommendations by 91 medical experts based on scholarly medical research. It’s a good starting point for us because it helpfully summarizes the meaning and implications of recent research findings.

Their assertion is that even though the FDA has long considered Tylenol safe for use during pregnancy, increasing experimental and epidemiological research suggests that prenatal exposure to acetaminophen increases the risks of neurodevelopmental, reproductive and urogenital disorders in children. For our purposes, we will focus on the neurodevelopmental risks.

Observational studies in kids suggest an association between prenatal exposure to acetaminophen and increased risk of attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), language delay in girls, and decreased intelligence quotient (IQ). Experimental studies in animals have found that fetal exposure to acetaminophen induced brain changes that affected cognitive function, behavior, and even movement. These effects depend on the timing, duration, and dosage of prenatal acetaminophen exposure.

These medical experts recommend that pregnant women be given the following advice:

  1. Forego using acetaminophen unless medically indicated.
  2. Consult with their doctor if they are uncertain if using acetaminophen is indicated and before using on a long-term basis.
  3. Minimize risk by using the lowest effective acetaminophen dose for the shortest possible time.

Autism and Tylenol Research Study 2: Association of cord plasma biomarkers of in utero acetaminophen exposure with risk of attention deficit/hyperactivity disorder and autism spectrum disorder in childhood

This important 2020 study that the National Institutes of Health (NIH) funded measured the amount of acetaminophen found in the umbilical cord blood of 996 births. These researchers wanted to find out whether the amount of acetaminophen found within that umbilical cord blood was associated with a diagnosis of ADHD or autism by the time these children reached 9 years of age. They classified the children by the amount of acetaminophen within their umbilical cord blood into three groups–lowest, middle, and highest.

Compared to the lowest third, kids in the middle third for acetaminophen concentration were at 2.26 times the risk for ADHD and 2.14 times the risk for autism. Kids in the highest third for acetaminophen concentration were at 2.86 times the risk for ADHD and 3.62 times the risk for autism compared to the lowest third of children.

In summary, fetal exposure to acetaminophen was associated with significantly increased risk of childhood ADHD and autism spectrum disorder. Their takeaway is that in utero exposure to acetaminophen is associated with increased risk of ADHD and autism in kids.

Their findings indicate that fetal exposure to acetaminophen is associated with a significantly increased risk of childhood autism in a “dose-response fashion.” This association of autism and Tylenol continued to hold during their sensitivity and subgroup analyses “across strata of potential confounders, including maternal indication, substance use, preterm birth, and child age and sex.”

This is a significant research paper and possibly the most powerful evidence about autism and Tylenol because its study design is quasi-experimental. A quasi-experimental study design is the next most powerful research design after an experimental or randomized controlled trial research design. Practically speaking for this topic, this is effectively the most powerful study design, because, for ethical reasons, scientists cannot conduct an experiment with pregnant mothers and randomly assign them different doses of acetaminophen. Instead, by using previously collected umbilical cord blood, researchers were able to compare naturally occurring acetaminophen dosage effects on ADHD and autism diagnoses without having to conduct such an experiment themselves. They could not control the acetaminophen doses ahead of time as they would in an experiment, but given an existing historical record of acetaminophen dosages, they could determine acetaminophen dosage effects on ADHD and autism diagnoses.

Learn more about Dr. Stanley Greenspan and the Greenspan Floortime approach. If you are new, we have a background and introduction to Greenspan Floortime including how it helps special needs children. We also have Greenspan Floortime training courses at Floortime U. specifically designed for parents and professionals including the Floortime Manual.