This announcement has caused alarm and confusion worldwide. But despite Trump’s claim, there is no strong scientific evidence to back it up. Our study of nearly 2.5 million births in Sweden published in 2024 shows no evidence that acetaminophen use during pregnancy increases a child’s risk of autism. This is the largest study conducted on the subject to date.

To understand whether acetaminophen really poses a risk in pregnancy, we turned to Sweden’s national health registers, which are among the most comprehensive in the world. Our study followed nearly 2.5 million children born between 1995 and 2019, tracking them for up to 26 years.

Using prescription records and interviews that midwives conducted during prenatal visits, we could see which mothers reported using acetaminophen (about 7.5% of pregnancies) and which did not.

We also made sure to account for any variables that may have affected the results of our statistical analysis – including controlling for health factors, such as fever or pain, which would have influenced whether or not a mother used acetaminophen during her pregnancy. This was to ensure a more fair comparison between the two groups.

We then looked at the children’s neurodevelopmental outcomes – specifically whether they were diagnosed with autism, ADHD or an intellectual disability.

The real strength of our study came from being able to compare siblings. This allowed us to compare children born to the same mother, where acetaminophen had been used during one child’s pregnancy but not the other. We compared over 45,000 sibling pairs, where at least one sibling had an autism diagnosis.

This sibling design is powerful because siblings share much of their genetics and family environment. This allows us to tease apart whether the drug itself – rather than underlying family traits or health conditions – is responsible for any apparent risks for neurodevelopmental outcomes.

Acetaminophen use

When we first looked at the entire population, we saw a pattern that echoed earlier studies: children whose mothers reported using acetaminophen during pregnancy were slightly more likely to be diagnosed with autism, ADHD or an intellectual disability.

But once we ran the sibling comparisons, that association completely disappeared. In other words, when we compared sets of siblings where one was exposed in the womb to acetaminophen and one was not, there was no difference in their likelihood of later being diagnosed with autism, ADHD or an intellectual disability.

Our study is not the only one to put this question to the test. Researchers in Japan recently published a study using a similar sibling-comparison design, and their results closely matched ours.

Importantly, they replicated our findings in a population with a different genetic background and where patterns of acetaminophen use during pregnancy are quite different. Nearly 40% of mothers in Japan reported using the drug during pregnancy. In comparison, less than 10% of Swedish mothers had used it.

Despite these differences, the conclusion was the same. When siblings are compared, there is no evidence that acetaminophen use during pregnancy increases the risk of autism or ADHD.

These findings mark an important shift from earlier studies, which relied on more limited data, used smaller cohorts and didn’t account for genetic differences. They also did not fully account for why some mothers used pain relief during pregnancy while others didn’t.

For example, mothers who take acetaminophen are more likely to also have migraines, chronic pain, fever or serious infections. These are conditions that are themselves genetically linked to autism or ADHD, as well as a child’s likelihood of later being diagnosed with one of these conditions.

These types of “confounding factors” can create associations that look convincing on the surface, but may not reflect a true cause-and-effect relationship.

That brings us to the real question on many people’s minds: what does this mean if you’re pregnant and dealing with pain or fever?

It’s important to recognise that untreated illness during pregnancy can be dangerous. A high fever in pregnancy, for example, is known to increase the risk of complications for both mother and baby. “Toughing it out,” as the president suggested, is not a risk-free option.

That’s why professional medical organisations such as the American College of Obstetricians and Gynecologists and the UK’s Medicines and Healthcare products Regulatory Agency continue to recommend acetaminophen (paracetamol) as the safest fever reducer and pain reliever during pregnancy when used at the lowest effective dose and only when necessary. This has been the guidance for decades.

Of course, if someone finds themselves needing to take acetaminophen regularly over a longer period of time, that’s a decision best made in consultation with their doctor or midwife. But the idea that acetaminophen use during pregnancy causes autism simply isn’t supported by the best available science.

The greater danger is that alarmist messaging will discourage pregnant women from treating pain or fever – putting both themselves and their babies at risk.

Renee Gardner, Principal Researcher, Department of Public Health Sciences, Karolinska Institutet; Brian Lee, Professor of Epidemiology, Drexel University, and Viktor H. Ahlqvist, Postdoctoral Researcher, Institute of Environmental Medicine, Karolinska Institutet

This article is republished from The Conversation under a Creative Commons license. Read the original article.