Fever is More Dangerous Than Medication
Many pregnant women hesitate to take medication even when their temperature rises to 38–39°C due to a cold. Whether they are suffering from severe headaches or body aches, the concern that “it might harm the baby” comes first.
On the internet, posts claiming that “taking Tylenol during pregnancy can cause Autism Spectrum Disorder (ASD) in children” are still easily found. The anxiety has grown further as even prominent overseas politicians have mentioned such possibilities.
However, a large-scale study recently analyzing over 700,000 mothers and children has yielded results that force us to rethink the so-called “Tylenol fear.”
The study concluded that it found no evidence to support the claim that taking acetaminophen—the main ingredient in Tylenol—during pregnancy increases the risk of a child developing ASD or Attention Deficit Hyperactivity Disorder (ADHD).
In fact, obstetricians have long recommended Tylenol as a primary antipyretic and analgesic safe for use by pregnant women.
As the number of medications safe for use during pregnancy is limited, it is one of the first options chosen when fever or pain occurs. Nevertheless, many pregnant women choose to endure the pain rather than take the medicine due to the vague anxiety that “medication that crosses the placenta affects the fetus.”
It is true that acetaminophen crosses the placenta, and some observational studies have previously reported that children born to mothers who took the drug during pregnancy showed higher rates of ASD or ADHD. Following the publication of these studies, the controversy surrounding Tylenol has persisted for over a decade.
However, the medical community has pointed out a common limitation in these previous studies. Mothers who took Tylenol during pregnancy were not simply people who took the drug; they were likely people who were ill enough to require it, such as those suffering from high fever, infection, or chronic pain.
When diverse variables such as genetic factors, family environment, and parental health status are added, it is difficult to accurately isolate the effect of the drug itself. In other words, previous studies could not conclude whether the impact on the child’s development was truly caused by Tylenol, or by the mother’s illness or family characteristics.
This is exactly why this new study is receiving such attention.
A joint research team from the University of Hong Kong and Aston University in the UK analyzed medical records of approximately 708,000 mother-child pairs registered in the Hong Kong public health system from 2001 to 2023, choosing to compare siblings born to the same parents.
They identified cases where the mother took Tylenol in one pregnancy but did not in another. Because siblings share most of their genetic background and living environment, this method significantly reduces the impact of familial factors that plagued previous studies. This is why the medical community considers sibling-comparison studies to be of higher reliability than general observational studies.
The results of the analysis were clear.
Children born to mothers who took acetaminophen during pregnancy did not show an increased risk of ASD or ADHD compared to those who did not. Even when analyzed by splitting the pregnancy into the first, second, and third trimesters, or by checking whether the drug was taken during one period versus multiple periods, or by looking at cumulative dosage, no meaningful differences were found.
In fact, the signals of increased risk seen in existing general cohort studies disappeared in the sibling comparison. The research team explained that some of the associations reported to date likely reflect the influence of common factors such as genetic traits, family environment, or maternal health status, rather than the drug itself.
This study does not mean that one can safely take any medication during pregnancy. Medication during pregnancy can have vastly different effects on the fetus depending on the type, timing, and dosage, so the judgment of medical staff must always come first.
However, the common view in the recent academic community is that the basis for unconditionally avoiding even recommended doses of Tylenol in medically necessary situations is becoming increasingly weak.
Rather, obstetricians explain that leaving a high fever untreated for a long time during early pregnancy can exacerbate maternal dehydration and inflammatory responses, and a sustained state of hyperthermia can be a burden to the fetus, making appropriate fever treatment more important.
Ultimately, this study serves as another scientific verification of the long-standing anxiety that “taking Tylenol during pregnancy causes autism.”
This study once again demonstrates that trusting evidence obtained through large-scale medical data and sophisticated research designs is a safer choice for both mother and fetus than fragmentary information or unverified anecdotes floating around the internet.
Furthermore, in medical treatment processes—including preparing for In Vitro Fertilization (IVF), ovulation induction, egg retrieval, and before or after embryo transfer—acetaminophen (Tylenol) is generally considered one of the top priorities for fever and pain relief when medical treatment is needed.
Studies to date have found no evidence that acetaminophen taken at recommended doses during IVF treatment adversely affects pregnancy success rates, implantation, or the neurodevelopment of the fetus. However, as with any other medication, it is safest to consult with your fertility specialist before taking it.
※ This article is based on the joint study by the University of Hong Kong and Aston University published in the JAMA Internal Medicine, as well as international clinical guidelines and the latest medical research regarding medication use during pregnancy. Medical judgment and treatment decisions must always be made through consultation with professional medical staff.
※ Image: AI-generated (ChatGPT, OpenAI) / Reference visual aid for better understanding.