Understanding autism: Facts about causes, medications, and vaccines

Autism is a neurodevelopmental condition that often presents in early childhood. Autistic people are creative, honest, and loyal. They have excellent memory abilities, strong attention to detail, expertise in their favorite topics, and often engage in periods of hyper focus. Autism is also characterized by difficulties in social communication and interactions (e.g., limited back-and-forth interactions, eye contact and gestures, and difficulties developing, maintaining, and understanding relationships), and can include the presence of restricted and/or repetitive patterns of behaviour, interests, or activities (e.g., insistence of sameness). Autism varies widely in its presentation, including language and cognitive ability, and level of supports needed. Autism is extremely heterogenous, meaning if you have met one person with autism, you have met one person with autism.

Autism has become increasingly prevalent in Canada and globally, with the Public Health Agency of Canada’s most recent estimates identifying 1 in 50 children and youth as having autism. While autism has been diagnosed since the 1950s, there has been an increase in rates of diagnosis in the last 20 years. This is partially due to improvements in our understanding of the variety of ways autism can present, as well as improved assessment measures that have become better at identifying more subtle presentations of autism. Males are diagnosed more frequently than females at a ratio of approximately 4:1; however, it is unknown if this is because autism is more common in males or whether other factors result in females being missed in the diagnostic process. 

Autism is a complex condition that does not have a single known cause. Although research around the world is ongoing, current evidence shows that autism arises from a combination of genetic and environmental factors. Researchers have spent decades conducting numerous studies – including cohort studies, case-control studies, population-based studies, and meta-analyses – examining various proposed causes, such as vaccines and acetaminophen during pregnancy. 

Recent studies have examined whether the use of acetaminophen (also known as Tylenol) during pregnancy is associated with autism. While some observational studies have suggested a possible association, these studies have significant limitations. It is essential to recognize that correlation does not imply causation, and numerous factors—such as underlying conditions that necessitate pain relief, fever, infection, or inflammation during pregnancy—complicate isolating the effect of acetaminophen itself. In fact, after controlling for genetics via the use of sibling controls, a large Swedish study found no association between acetaminophen use and autism. 

Pregnant individuals may experience pain, fever, or other symptoms that require treatment. Leaving these conditions untreated can pose serious risks to both maternal and fetal health. Acetaminophen remains the recommended first-line pain reliever and fever reducer during pregnancy when used as directed. It has been used safely by millions of pregnant people for decades. The Society of Obstetricians and Gynaecologists of Canada (SOGC) released a position statement Sept. 12, 2025, reaffirming that “the use of acetaminophen is an important first-line therapeutic option for fever and pain in pregnancy when medically indicated at recommended doses for the shortest duration required”. Other pain medications, such as NSAIDs (non-steroidal anti-inflammatory drugs like ibuprofen/Advil), are generally not recommended during pregnancy due to known risks to the developing fetus. As with any medication during pregnancy, individuals should consult with their healthcare providers about appropriate pain management and follow their doctor's recommendations.

The facts on vaccines, autism, and child health

Vaccines are among the most important public health tools we have, and they are rigorously tested for safety and effectiveness before approval for use and following their introduction. Vaccination during pregnancy protects both the pregnant person and their developing baby from serious infections that can cause complications during pregnancy and in early infancy. Childhood vaccines protect children from potentially life-threatening and life-altering diseases such as measles, mumps, rubella, whooping cough, and others. 

Despite extensive research and robust evidence definitively showing that vaccines, including the MMR vaccine, do not cause autism, vaccine hesitancy persists in some communities, often fueled by misinformation or discredited studies. In 1998, a study suggested a link between the MMR vaccine and autism. This study has since been discredited due to methodological and ethical flaws, biased research, and conflicts of interest, leading to the study author having his medical license revoked. Since then, there have been many follow-up studies with millions of children that have investigated whether there is a credible link between the MMR vaccine and autism, and health experts and scientists have concluded that there is no link between the MMR vaccine and autism.

Healthcare providers are the best source of evidence-based information about vaccine safety and timing, and parents should feel empowered to discuss any concerns with their doctors. Following recommended vaccination schedules protects not only individual children but also vulnerable members of our community who cannot be vaccinated due to age or medical conditions, through what is known as herd immunity.

Autism is a complex neurodevelopmental condition and is likely ‘caused’ by the interaction between multiple genetic and environmental factors, that have yet to be credibly determined. Existing research has not identified a single cause; however, reliable evidence has excluded several potential contributors. The neurodiversity movement and Autism advocates emphasize the importance of research focusing on how to best support Autistic people to navigate their worlds successfully and thrive, versus focusing on a cure. Moving away from viewing autism in terms of "causes"—which suggests a problem to be solved—and instead concentrating on "supports"—which emphasize enhancing well-being—encourages acceptance, affirms autistic identity, and centers long-term flourishing and quality of life. Conversations about autism diagnoses and supports are complex and should be done in partnership between Autistic people, their caregivers, and clinicians. Autistic people and their caregivers bring valuable lived experience and expertise that complement clinical expertise; by valuing this lived experience as evidence, clinicians enable shared decision making, leading to increased satisfaction and improved outcomes.

A note on identity-first language

NB: There are various ways to describe autism, each with its own justification (Kenny et al., 2016). Traditionally, person-first language (e.g., “person with autism”) has been used to emphasize the individual before the disability (Vivanti, 2020). In contrast, identity-first language (e.g., “Autistic person”) asserts that autism is a permanent and important part of a person’s identity (Dwyer, 2022). While there is no universally agreed-upon terminology for describing autism (Kenny et al., 2016), most Autistic individuals prefer identity-first language (e.g., Botha et al., 2021a; Bury et al., 2020; Kenny et al., 2016; Taboas et al., 2022). This preference underscores the view that autism is inseparable from the individual and is an aspect of an individual’s identity that they may take pride in (Dwyer, 2022). As a result, identity-first language is used to respect the preference of most of the Autistic community.

Authors:

Dr. Carly McMorris, PhD, RPsych

Associate Professor, Werklund School of Education

Canada Research Chair (Tier II) Neurodiversity and Mental Health

Owerko Centre

University of Calgary

Dr. Kathryn Kenny, MD, FRCSC

Deputy Department Head, Obstetrics

Clinical Assistant Professor, Department of Obstetrics and Gynecology

Alberta Health Services & Cumming School of Medicine, University of Calgary

Dr. Kirsten Fiest, PhD

Professor, Department of Critical Care Medicine

Scientific Director, O’Brien Institute for Public Health

Cumming School of Medicine

University of Calgary

*We are grateful to the parents of neurodiverse children who reviewed this statement and provided feedback