Autism and Acetaminophen: Update

Subjectivity in secondary research
retains the confounding factors
present in observational studies

Acetaminophen – Autism Update (1/19/26)

by Ron Fritz, PhD

Following last Friday’s CEH article, Autism, Acetaminophen, and Human Genetic Health (1/16/26), interest in this topic remains high. On the same day, a new study was published and has now been summarized (Monday, 1/19/26) on the medical news website Medical Xpress. The summary, authored by City St George’s, University of London, is titled: “Taking acetaminophen during pregnancy does not increase risk of autism, ADHD or intellectual disabilities.”

Before addressing this summary, let’s briefly review the study itself. The research, “Prenatal paracetamol exposure and child neurodevelopment: a systematic review and meta-analysis,” is secondary research. Unlike primary research, it does not collect new data from participants. Instead, the authors systematically identified all relevant existing studies using pre-defined criteria aimed at minimizing selection bias (the systematic review component) and quantitatively combined the results to produce a single pooled estimate of effect (the meta-analysis component). Essentially, this approach treats multiple studies as a single larger dataset, generally increasing statistical power.

In this case, 17 studies were deemed comparable enough for inclusion. While pooling increases sample size (and statistical power), it is not without limitations. Differences in study design, populations, exposure definitions, outcome measurements, and confounder adjustment introduce heterogeneity (variability), which can reduce the reliability of the pooled estimate. Furthermore, the inherent confounding present in observational studies—discussed in the 1/16/26 CEH article—remains. Pooling multiple studies that differ in these ways does not always produce clearer insights.

The study’s authors conclude:

“Current evidence does not indicate a clinically important increase in the likelihood of autism spectrum disorder, ADHD, or intellectual disability in children of pregnant individuals who use paracetamol as directed, supporting existing recommendations on its safety.”

This contrasts with previous meta-analyses, which suggested increased risk for autism and ADHD but were hampered by high between-study variability. Differences in outcomes often reflect which studies are included and the analytical methods used. This new meta-analysis incorporated sibling comparison studies (two studies), which is valuable, and assessed study quality using the QUIPS tool (Quality in Prognosis Studies), which previous analyses did not. While QUIPS provides a structured framework for risk-of-bias assessment, it is subjective rather than quantitative, meaning reasonable researchers may interpret study selection differently.

Overall, this analysis is well-executed and a valuable addition to the evidence base. However, it does not end the debate, despite the provocative Medical Xpress headline. Statements suggesting certainty—such as “it was confirmed that taking acetaminophen in pregnancy was not linked to childhood autism, ADHD or intellectual disability”—overstate what the evidence can support. Even high-quality meta-analyses cannot fully resolve uncertainty, and judgments of study quality remain subjective. Reasonable scientists may still reach differing conclusions.

• D’Antonio, F., Flacco, M. E., Della Valle, L., Prasad, S., Manzoli, L., Samara, A., & Khalil, A. (2026). Prenatal paracetamol exposure and child neurodevelopment: a systematic review and meta‑analysis. The Lancet Obstetrics, Gynaecology, & Women’s Health. https://doi.org/10.1016/S3050‑5038(25)00211‑0.

Ronald D. Fritz, PhD, is a retired research statistician whose career spanned 27 years. Before entering the field of statistics, he worked as an engineer and engineering manager in the defense industry. He earned his doctorate in Industrial Engineering, with a minor in Mathematical Statistics, from Clemson University, where he was honored as a Dean’s Scholar.

Dr. Fritz served as a consulting statistician across a broad range of industries, culminating in a 12-year role as a global statistical resource at PepsiCo. During his time at PepsiCo, he led significant research on gluten contamination in oats and its relationship to celiac disease, publishing several articles on the subject.

In retirement, Dr. Fritz developed a deep interest in creation science, sparked by a visit to the Creation Museum in Petersburg, Kentucky. As he delved into the topic, he shared his findings with his pastor, which led to an invitation to speak at their church. This initial presentation opened the door to further speaking engagements at churches throughout the region.

Dr. Fritz has been married for 35 years to his wife, Mitzie. They live in the mountain community of Bee Log, North Carolina, within sight of the church where they were married and now worship. In his free time, Dr. Fritz tends a small chestnut orchard on their property, working to revive what was once a cherished local delicacy. The couple has two adult children.