Author: Dr. Danielle Baribeau, MD, PhD, Clinician Scientist/Psychiatrist, Holland Bloorview Kids Rehabilitation Hospital | Editors: Tashi Stampp and Romina Garcia de leon (blog coordinators)
Why is there an ongoing debate surrounding the potential effects of Tylenol use during pregnancy?
Acetaminophen (Tylenol) is one of the safest and most widely used medications for pain control and treatment of fever in pregnancy. There has been renewed political focus on autism research in the USA, and there was a systematic review published last year in 2025 that seemed to bring attention to this topic again.
Does current scientific evidence show that Tylenol use during pregnancy causes autism? What is the difference between true cause and possible association?
The current evidence does not suggest that acetaminophen causes autism. There have been a number of studies suggesting that if you compare groups of autistic children to groups of non-autistic children, those diagnosed with autism were slightly more likely to have been exposed to acetaminophen in pregnancy, but the difference between groups is small (less than a 1% difference). High quality studies that have looked at this have shown that the difference is explained by the health of the mother/ pregnant parent. Mothers with a history of pain disorders, high fevers, health problems, or migraine, for example, are slightly more likely to have a child diagnosed with autism, and are also more likely to take Tylenol. Maternal fever in pregnancy has been shown to be associated with a slight increased likelihood of autism. So while there may be a correlation between Tylenol exposure and autism in some datasets, it does not mean one causes the other. Also, it’s important to remember that these associations are all very small, so while they’re worth studying from a population level perspective, it’s not something that individual families need to worry about nor can control.
Which is the safer route: taking Tylenol during pregnancy or managing fever without medication?
Health decisions in pregnancy are a risk-benefit discussion that should take place between a pregnant person and their doctor. The American College of Obstetrics and Gynecology have put forward some guidance about this: https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2025/09/acetaminophen-use-in-pregnancy-and-neurodevelopmental-outcomes We know that untreated health problems in pregnancy can adversely effect the mother, and inadequate treatment of pain can impact mental health, wellbeing and stress, having negative consequences for both the mother and fetus. Avoiding a treatment that could potentially help due to unsubstantiated fear of the treatment risks harming both mother and child.
Do scientists know what causes autism? Also, what can explain the increase of Autism diagnosis?
Autism does not have a single cause, but we know it is not caused by vaccines or parenting style. Many factors interact together to shape the likelihood of autism. We know genetics play a major role. Currently, about 20% of autistic individuals can now be diagnosed with an underlying rare genetic condition that explains their developmental differences. It’s important to remember that “genetic” doesn’t necessarily mean inherited. Autism can, but does not necessarily, run in families. Many rare genetic conditions associated with are new and unique to the autistic individual.
The rising rate of autism diagnosis can largely be explained by increased understanding and recognition of the variety of ways autistic traits can present. For example, autism can present differently in girls/ women, making it harder to diagnose. In the past, people who had more subtle presentations of autism, or people with other co-occurring conditions (mental health, intellectual disability, ADHD) were often missed. Many of our school supports, health systems, and treatment programs currently require people to be “diagnosed” with a condition in order to access services, support and funding. For this reason, rates of diagnosis are rising. Ultimately, increased diagnosis allows people to access the supports and services they need.
How does your research influence the lives of Canadian families? What important points should new parents consider regarding their newborn’s health?
My research program is focused on 1) describing the mental health concerns and mental health care needs of children and youth with neurodevelopmental disorders, including autism, and 2) understanding the clinical profiles associated with the growing number of ultra-rare genetic conditions that are being discovered. This work can help kids, families and clinicians anticipate support needs and individualize treatment, and can help shape health systems to better meet the needs of neurodivergent people.
For new parents, I would emphasize that all children are unique. Figuring out how best to support them, including the 10 to 20% who are developing differently, is the task, the challenge and the joy of parenting. With respect to autism, to quote my colleague Dr. Melanie Penner, “We should recognize autism as a valuable expression of human diversity, while also recognizing every individual’s unique needs.” Families should be sure to follow the recommended vaccine schedule for their newborn, and seek advice from a medical professional if they have questions about autism diagnosis and treatment.