Does Paracetamol Cause Autism in Pregnancy?

Recent information from studies linking paracetamol/acetaminophen (Tylenol) use in pregnancy to autism disorders have popularised on the internet massively in August/September 2025, which has caused nationwide concern about mothers taking these painkillers when they are expected to have a baby.

The information surrounding this comes from studies that are observational cohort studies, reporting statistical association between paracetamol exposure in pregnancy and increased risk of neurodevelopmental disorders like autism and attention-deficit/hyperactivity disorder. The key word here is "association".

Association and causation are two different terms used in scientific studies, with causation meaning a direct established link between paracetamol use in pregnancy to autism, and not just an association that there may be a higher chance that some pregnant women who have taken paracetamol have had an autistic child.

Studies that suggest association

There are observational studies and analyses of information that suggest the association [1,2]. The issue with these association studies is that they are likely explained by confounding factors like fevers or genetics, which are factors that explain the association observed, but this association can be false or exaggerated, and without direct causal links, these cannot fully provide evidence that paracetamol use in pregnancy causes autism. For example, mothers may take paracetamol because they had a fever or infection, which are associated with increased risk of developmental issues in children [3]. But here, the true underlying factor is the untreated fever/infection, not the exposure to paracetamol.

Another factor is shared genetics. Autism has a genetic component to it, so if a mother is experiencing greater pain sensitivity or inflammatory conditions that are linked to autism, they may be more likely to take paracetamol, but again, this doesn't mean the drug has caused autism in the child, but rather the mother's genetics.

Studies that do not suggest association

These sibling-controlled studies compare a child who was exposed to paracetamol in pregnancy with their sibling who was not exposed or exposed less, the association between autism largely disappeared, with no consistent effect across siblings. Sibling studies account for genetic and environmental confounding factors, making them strong studies, and explain that the link that was shown before was likely down to other confounding factors [4]. Whilst this is not a causation study, because a mother may have had fevers in one pregnancy and not another so the fever could be the hidden cause, and these studies cannot remove that confounding factor, it does still suggest that paracetamol is not the primary reason for autism.

Causation studies?

True causation studies are done by randomised controlled trials, where random pregnant women would be exposed to paracetamol and others would be exposed to a placebo to track if autism developed, but this is highly unethical. Animal studies can provide biological plausibility but the translation to humans gives inconsistent results.

Studies done using mice have suggested that exposure to paracetamol affects their memory and learning and increases markers of oxidative stress in the brain, which can be linked to developmental disorders through neuronal damage [5]. Other studies disagree with this and say there was no evidence of developmental disorders in mice when exposed [6]. But again, this cannot be done in humans due to ethical reasons, and the strongest human studies point to association through confounding factors.

Pregnant women should always take the advice of their doctor, and we should bear in mind that the World Health Organisation also has stated there is no conclusive scientific evidence between autism and paracetamol use in pregnancy, with paracetamol being one of the safest painkillers to take whilst pregnant [7].

References

1. Masarwa R, Levine H, Gorelik E, Reif S, Perlman A, Matok I. Prenatal Exposure to Acetaminophen and Risk for Attention Deficit Hyperactivity Disorder and Autistic Spectrum Disorder: A Systematic Review, Meta-Analysis, and Meta-Regression Analysis of Cohort Studies. American Journal of Epidemiology. 2018 Apr 24;187(8):1817–27.

2. 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 [Internet]. 2019 Oct 30;77(2):1.

3. Hornig M, Bresnahan MA, Che X, Schultz AF, Ukaigwe JE, Eddy ML, et al. Prenatal fever and autism risk. Molecular Psychiatry. 2017 Jun 13;23(3):759–66.

4. Ahlqvist VH, Sjöqvist H, Dalman C, Karlsson H, Olof Stephansson, Johansson S, et al. Acetaminophen Use During Pregnancy and Children’s Risk of Autism, ADHD, and Intellectual Disability. JAMA [Internet]. 2024 Apr 9 [cited 2024 Apr 11];331(14):1205–5.

5. Philippot G, Hosseini K, Yakub A, Mhajar Y, Hamid M, Buratovic S, et al. Paracetamol (Acetaminophen) and its Effect on the Developing Mouse Brain. Frontiers in Toxicology. 2022 Mar 22;4.

6. Kougias DG, Atillasoy E, Southall MD, Scialli AR, Ejaz S, Chu C, et al. A quantitative weight-of-evidence review of preclinical studies examining the potential developmental neurotoxicity of acetaminophen. Critical reviews in toxicology [Internet]. 2025 Spring;1–55. Available from: https://pubmed.ncbi.nlm.nih.gov/39982125/

7. World. WHO statement on autism-related issues [Internet]. Who.int. World Health Organization: WHO; 2025. Available from: https://www.who.int/news/item/24-09-2025-who-statement-on-autism-related-issues

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