Acetaminophen and Autism
Based on the scientific evidence we now know that many, if not most, cases of autism are a chemically-induced injury which occurs when babies and children with oxidative stress are given acetaminophen (commonly branded Tylenol in the U.S.).​
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To learn more about the 24 reasons, or lines of evidence, that led to this conclusion scroll down, or select the audience that best fits your interests to read about what to do next.
Evidence Overview
24 and Counting
Currently there are 24 lines of peer-reviewed and published reasons (also called lines of evidence) we know autism is a chemically-induced injury from acetaminophen. This will continue to be updated as more evidence is uncovered, peer-reviewed- and published.
Categorizing the Evidence
Why did we make categories? We want this to be as easy to understand as possible, and with categories we can give you a quick overview before diving in. While this does not reflect the importance of the lines of evidence, it's a great way to easily scan and remember the topics.
Category 1
Pre- and Post- Natal Associations
The prenatal (pregnancy) and postnatal (after birth) periods of time are when the human brain develops most rapidly, and when direct associations between acetaminophen use and autism are most clear.
The lines of evidence related to pre- and post-natal associations make up 16.7% of the total evidence.
01
Use of acetaminophen during pregnancy is connected to negative long-term effects
Use of acetaminophen during pregnancy is associated with lower IQ, autism, and ADHD in children
02
Levels of acetaminophen in cord blood are associated with autism
Higher levels of acetaminophen in the baby's umbilical cord at the time of birth are strongly associated with autism
03
Acetaminophen use during early childhood is connected to 20-times more regressive autism
Children exposed to acetaminophen in early childhood are much more likely to have regressive autism (associated with loss of developmental milestones) than children who are not
04
Babies with acetaminophen exposure after birth were found to be 30% more likely to have autism
A study of the Danish National Birth Cohort found an odds ratio (OR) of 1.3 for autism associated with postnatal acetaminophen exposure
*Correlation doesn’t necessarily prove causation, but correlation is necessary for causation to exist. Multiple correlations with numerous other lines of evidence can be conclusive.
Category 2
05
Autism increased at the same time that acetaminophen started replacing aspirin in the market
The amount of autism began to increase in the early 1980s, coinciding with the increase in acetaminophen use after aspirin was associated with Reye’s syndrome
06
Ratio of regressive to infantile autism shifted at the same time acetaminophen replaced aspirin for use in babies and children
The ratio of regressive to early-onset (infantile) autism rose at the same time as pediatric acetaminophen use rose after aspirin was associated with Reye’s syndrome
07
As direct-to-consumer advertising increased, use of acetaminophen and autism also rose in prevalence
The amount of autism steadily increased as direct-to-consumer advertising and perhaps other factors have driven up use of pharmaceutical products
Associations in Time
Associations in time are two or more things changing over the same time period. Evaluating these associations can provide valuable clues that suggest possible causal relationships.
The lines of evidence related to associations in time make up 12.5% of the total evidence.
*Correlation doesn’t necessarily prove causation, but correlation is necessary for causation to exist. Multiple correlations with numerous other lines of evidence can be conclusive.
Category 3
Animal Studies
Animals are biologically very similar to humans, they are susceptible to many of the same health problems as humans, and their shorter life cycles enable us to study them throughout their whole life span.
The lines of evidence related to animal studies make up 16.7% of the total evidence.
08
Long-term behavioral changes occur when mouse and rat pups are exposed to acetaminophen
Laboratory mice and rats show long-term behavioral changes when given acetaminophen at a very young age
09
Acetaminophen exposure in early life negatively affects social function in male brains more than in female brains
The effects of acetaminophen and related drugs hurt social function in male brains more than in female brains
10
Acetaminophen kills nerve cells in the brain in adult lab animals
Acetaminophen causes death of cortical neurons in adult laboratory rats at concentrations lower than it causes liver failure
11
Acetaminophen is toxic to cats because they are missing a critical "pathway", same as babies
Normal doses of acetaminophen are toxic in cats because they are deficient in 'the glucuronidation pathway" of metabolism. Newborn babies are also deficient in this metabolic pathway
Category 4
Associations in Human Activity
Associations with human activity help us to understand and quantify the impact of our actions. Such associations can involve medical procedures, drug manufacturing, or use of drugs during different times of life.
The lines of evidence related to associations in human activity make up 29.2% of the total evidence.
12
Circumcised individuals have 2 times more infantile autism
Male circumcision, often performed using acetaminophen as a pain reliever, is associated with a 2x increase in early-onset (infantile) autism
13
An unexpectedly high prevalence of autism was found at the same time that acetaminophen products for children were repeatedly manufactured with too much active ingredient
An unexpectedly high prevalence of autism was identified in South Korea, where acetaminophen-containing products for children were repeatedly found to contain amounts of drug exceeding the package label
14
Orthodox Jews, who do not traditionally use acetaminophen, have a substantially lower prevalence of autism
Ultra-Orthodox Jews and Arabs in Israel have reported prevalence of autism less than half of that of other Israelis. The use of alcohol, not acetaminophen, during traditional circumcision practices could account in part for their lower rates of autism
15
Administration of acetaminophen along with a vaccine is connected to autism
Acetaminophen given alongside vaccine administration but not vaccination alone is associated with autism
16
Up to 50% of parents who have a child with autism believe that vaccines were involved in the induction of their child's autism
Many parents believe that their children’s autism was induced by a vaccine based on their own observations. Acetaminophen is frequently used with vaccinations, although vaccinations alone do not cause autism
17
Autism is dramatically lower in very low-income countries with chronic shortages of common medications
Chronic and severe shortages of medications, including acetaminophen, in very low-income countries are associated with much less autism compared to other mental health disorders such as Down syndrome
18
In Denmark, acetaminophen is about twice as popular and similarly autism is about twice as prevalent as in Finland
From 2006-2010, the sales of acetaminophen in Denmark were more than two times greater than in Finland, and they had approximately 70% more autism than Finland
*Correlation doesn’t necessarily prove causation, but correlation is necessary for causation to exist. Multiple correlations with numerous other lines of evidence can be conclusive.
Category 5
Mechanisms of Action
Mechanisms of action are the way scientists talk about how something works, especially as it relates to the body. This evidence is not all specific to babies, but it all still sheds light on the way that acetaminophen interacts with human bodies.
The lines of evidence related to mechanisms of action make up 12.5% of the total evidence.
19
Acetaminophen is highly toxic in the presence of oxidative stress (when there's too many things for the body to "burn" or clean out)
Acetaminophen is known to be highly toxic in the presence of oxidative stress. The mechanism by which this toxicity occurs has been established for decades
20
Children with autism cannot metabolize acetaminophen well, which makes the drug much more toxic
Genetic and immune factors associated with an increased risk of autism have a detrimental effect on the body’s ability to metabolize acetaminophen, making the drug much more toxic
21
Individuals with cystic fibrosis are not prone to autism, and they also have metabolism that efficiently processes acetaminophen, which makes the drug much less toxic
Cystic fibrosis is associated with unusually efficient (effective) metabolism of acetaminophen, which makes the drug much less toxic, and concurrently some evidence suggests that the prevalence of autism may be very low in patients with cystic fibrosis
Category 6
22
Acetaminophen has never been proven to be safe for babies and children
Despite the fact that acetaminophen targets the brain, acetaminophen use in babies and children was only proven safe for short-term side effects, not for brain development
23
Multiple studies show acetaminophen affects the social function of the brain in adults
Acetaminophen use in adults temporarily blunts social trust and awareness, emotional responses to external stimuli, and the ability to identify errors, indicating that the drug targets regions of the brain affected in patients with autism
24
The similarities between autism and fetal alcohol spectrum disorder suggest that autism is chemically induced
The numerous similarities between autism spectrum disorder and fetal alcohol spectrum disorder, including complex phenotypes and associations with multiple genetic and environmental factors, suggest that both can be chemically induced
Miscellaneous
These lines of evidence do not fall neatly into any of the other categories, and yet are some of the most compelling.
The lines of evidence in the miscellaneous category make up 12.5% of the total evidence.
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