By: Dr. William Parker
How much decrease could we see if we stop the administration of acetaminophen in babies and children? It’s a burning question, and one that’s so critical for many parents, guardians, and those who care for babies and children.
We all share a deep desire to ensure the health and well-being of our children. Now that we have concluded without any reasonable doubt that exposure of susceptible children to acetaminophen causes “many if not most” cases of autism [1,2], there’s a reasonable responsibility to tell as many people as possible .
But so often the follow up question is “what’s the actual number?” “Many” could be only 10% or 20%, and “most” might only be 51%. So, what’s the actual number?
A lot of clues tell us that the actual number of cases of autism induced by acetaminophen could be the vast majority. And that’s a lot of cases, with one in every 36 children in the US now having autism .
Let’s look at some of these clues:
Before acetaminophen in babies and children became so popular, the prevalence of autism in the 1970s was only a tiny fraction of the current amount.
A consistent hallmark of autism is impairment in social awareness and studies in adult humans demonstrate that acetaminophen affects social awareness [4-6].
A lot of factors are associated with autism. These include everything from environmental toxins to problems that happen during birth, including preterm birth and jaundice. These factors all lead to something called “oxidative stress”, a condition which makes acetaminophen much more dangerous .
One really big indicator that acetaminophen might just be responsible for the vast majority of all cases of autism is the actual numbers being reported in various studies. Based on studies of the connection between autism and acetaminophen use during pregnancy [8, 9], we estimate that the number of cases of autism induced by acetaminophen exposure during pregnancy probably accounts for less than 20% and may account for 10% or less of the total cases. However, these cases add to the tally induced by exposure to acetaminophen after birth. At the time of birth, there is a VERY big association between acetaminophen exposure and autism. This can be seen in the infant’s blood at the time of birth . Another study showed that circumcision, a minor medical procedure associated with acetaminophen use, literally doubles the amount of infantile autism, the type of autism that appears before the baby’s brain develops social awareness . If we take both of these studies into account, a very rough guess is that 50% or 60% of all autism might be induced by acetaminophen at the time of birth. This estimate might seem ridiculous, but it does make sense from a scientific perspective . It turns out that pregnant women are extremely efficient at processing acetaminophen, and newborn babies are the worst ! So, with a snip of the umbilical cord, everything changes. The number of cases of autism induced later in life, after months of development, seems to be very high. A study by Stephen Schultz  found that almost all cases of “regressive autism”, the kind of autism that happens months after birth, is caused by acetaminophen . In addition, 30% to 50% of parents of children with autism think that a vaccine had something to do with their child’s autism [13, 14]. Since vaccinations are often associated with acetaminophen, and parent’s observations have historically been accurate when it comes to their child’s autism . Given this information, we can very roughly guess that, months to years after birth, acetaminophen induces around 30% of all autism.
That is quite the pile of clues. And those numbers add up: 10%-20% before birth, 50%-60% around the time of birth, and another 30% months to years after birth. That’s the vast majority.
The idea that acetaminophen induces the vast majority of cases of ASD is attractive from a scientific perspective because it satisfies something that is generally true in science: The simplest explanation that explains all of the observations is usually the correct explanation. (This is very similar to Occam’s Razor.)
Even with all of this research, we really can’t be sure at this point exactly how many cases of autism are induced by acetaminophen. Each of those studies I mentioned has uncertainty in it, and when you add up the studies, that uncertainty does not go away.
Although we aren’t certain about how much autism is caused by acetaminophen, we should make our best guess. At this point, we think that it’s very plausible that 90% or more of autism is caused by acetaminophen.
In the past, I thought that acetaminophen cannot possibly cause all cases of autism, since autism has been around since at least the 1940s, but acetaminophen was not used until the 1950s. But as it turns out, I was wrong. Two drugs (phenacetin and acetanilide) were used since the 1800s [15, 16] until they were determined to be very toxic and discontinued in the 1970s and 1980s [16, 17]. Both of those drugs are converted into acetaminophen by the human body [16, 18]. So, it is entirely possible that some of the first cases of autism reported in the 1940s  were induced by acetaminophen as a result of exposure to drugs that had been around for decades.
The only way we are ever going to know exactly how much autism is induced by acetaminophen is to stop using acetaminophen in babies and children, and probably during pregnancy. Once we stop administering acetaminophen while our children’s brains are in the early stages of development , we can monitor the levels of autism as the prevalence decreases, and will finally have our answer to exactly how “much.”
1. Patel E, Jones Iii JP, 3rd, Bono-Lunn D, Kuchibhatla M, Palkar A, Cendejas Hernandez J, et al. The safety of pediatric use of paracetamol (acetaminophen): a narrative review of direct and indirect evidence. Minerva pediatrics. 2022;74(6):774-88. Epub 2022/07/14. doi: 10.23736/s2724-5276.22.06932-4. PubMed PMID: 35822581.
2. Zhao L, Jones J, Anderson L, Konsoula Z, Nevison C, Reissner K, et al. Acetaminophen causes neurodevelopmental injury in susceptible babies and children: no valid rationale for controversy. Clinical and experimental pediatrics. 2023. Epub 2023/06/16. doi: 10.3345/cep.2022.01319. PubMed PMID: 37321575.
3. Maenner MJ, Warren Z, Williams AR, Amoakohene E, Bakian AV, Bilder DA, et al. Prevalence and Characteristics of Autism Spectrum Disorder Among Children Aged 8 Years - Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2020. Morbidity and mortality weekly report Surveillance summaries (Washington, DC : 2002). 2023;72(2):1-14. Epub 2023/03/24. doi: 10.15585/mmwr.ss7202a1. PubMed PMID: 36952288; PubMed Central PMCID: PMCPMC10042614.
4. Dewall CN, Macdonald G, Webster GD, Masten CL, Baumeister RF, Powell C, et al. Acetaminophen reduces social pain: behavioral and neural evidence. Psychol Sci. 2010;21(7):931-7. Epub 2010/06/16. doi: 10.1177/0956797610374741. PubMed PMID: 20548058.
5. Roberts ID, Krajbich I, Way BM. Acetaminophen influences social and economic trust. Scientific Reports. 2019;9(1):4060. doi: 10.1038/s41598-019-40093-9.
6. Mischkowski D, Crocker J, Way BM. A Social Analgesic? Acetaminophen (Paracetamol) Reduces Positive Empathy. Frontiers in psychology. 2019;10:538. Epub 2019/04/20. doi: 10.3389/fpsyg.2019.00538. PubMed PMID: 31001155; PubMed Central PMCID: PMCPMC6455058.
7. Parker W, Hornik CD, Bilbo S, Holzknecht ZE, Gentry L, Rao R, et al. The role of oxidative stress, inflammation and acetaminophen exposure from birth to early childhood in the induction of autism. J Int Med Res. 2017;45(2):407-38.
8. Alemany S, Avella-García C, Liew Z, García-Esteban R, Inoue K, Cadman T, et al. Prenatal and postnatal exposure to acetaminophen in relation to autism spectrum and attention-deficit and hyperactivity symptoms in childhood: Meta-analysis in six European population-based cohorts. Eur J Epidemiol. 2021;36(10):993-1004. Epub 2021/05/29. doi: 10.1007/s10654-021-00754-4. PubMed PMID: 34046850.
9. Liew Z, Ritz B, Virk J, Olsen J. Maternal use of acetaminophen during pregnancy and risk of autism spectrum disorders in childhood: A Danish national birth cohort study. Autism research : official journal of the International Society for Autism Research. 2016;9(9):951-8. Epub 2015/12/22. doi: 10.1002/aur.1591. PubMed PMID: 26688372.
10. Ji Y, Azuine RE, Zhang Y, Hou W, Hong X, Wang G, et al. Association of Cord Plasma Biomarkers of In Utero Acetaminophen Exposure With Risk of Attention-Deficit/Hyperactivity Disorder and Autism Spectrum Disorder in Childhood. JAMA Psychiatry. 2020;77(2):180-9. Epub 2019/10/31. doi: 10.1001/jamapsychiatry.2019.3259. PubMed PMID: 31664451; PubMed Central PMCID: PMCPMC6822099.
11. Frisch M, Simonsen J. Ritual circumcision and risk of autism spectrum disorder in 0- to 9-year-old boys: national cohort study in Denmark. J R Soc Med. 2015;108(7):266-79. doi: 10.1177/0141076814565942. PubMed PMID: PMC4530408.
12. Schultz ST, Klonoff-Cohen HS, Wingard DL, Akshoomoff NA, Macera CA, Ji M. Acetaminophen (paracetamol) use, measles-mumps-rubella vaccination, and autistic disorder. The results of a parent survey. Autism. 2008;12(3):293-307.
13. Freed GL, Clark SJ, Butchart AT, Singer DC, Davis MM. Parental vaccine safety concerns in 2009. Pediatrics. 2010;125(4):654-9. Epub 2010/03/03. doi: 10.1542/peds.2009-1962. PubMed PMID: 20194286.
14. Bazzano A, Zeldin A, Schuster E, Barrett C, Lehrer D. Vaccine-related beliefs and practices of parents of children with autism spectrum disorders. American journal on intellectual and developmental disabilities. 2012;117(3):233-42. Epub 2012/06/22. doi: 10.1352/1944-7558-117.3.233. PubMed PMID: 22716265.
15. Morris D, Haddy A, editors. Analgesic contents of patent medicines of the early 20th century: Bromo-Seltzer and Antikamnia. 264th ACS National Meeting; 2022 August 21-25, 2022; Chicago, IL.
16. Mahmud S, Rosen N. History of NSAID Use in the Treatment of Headaches Pre and Post-industrial Revolution in the United States: the Rise and Fall of Antipyrine, Salicylic Acid, and Acetanilide. Current pain and headache reports. 2019;23(1):6. Epub 2019/01/24. doi: 10.1007/s11916-019-0744-6. PubMed PMID: 30673879.
17. Ninan B, Wertheimer A. Withdrawing Drugs in the U.S. Versus Other Countries. Inov Pharm. 2012;3(3):Article 87.
18. Clissold SP. Paracetamol and phenacetin. Drugs. 1986;32 Suppl 4:46-59. Epub 1986/01/01. doi: 10.2165/00003495-198600324-00005. PubMed PMID: 3552585.
19. Kanner L. Autistic disturbances of affective contact. Nervous child. 1943;2(3):217-50.