50-70%
Co-occurrence rate (ADHD in autism)
Rommelse et al., 2010; Leitner, 2014 — meta-analyses
20-50%
Co-occurrence rate (autism in ADHD)
Antshel et al., 2016 — systematic review
2013 (DSM-5)
Year DSM allowed dual diagnosis
American Psychiatric Association, DSM-5
0.52 (moderate)
Methylphenidate effect size in autistic children
Rodrigues et al., 2019 — meta-analysis in J Child Psychol Psychiatry
The co-occurrence rate of 50-70% is established by multiple meta-analyses, including Rommelse et al. (2010) and Leitner (2014). The overlap is not simply diagnostic confusion — neuroimaging and genetic studies confirm shared neurobiological pathways involving executive function, attention regulation, and dopamine signaling.
Diagnostic assessment for dual ASD-ADHD requires careful differentiation of overlapping features. Both conditions can present with difficulty sustaining attention, social challenges, and emotional dysregulation. A comprehensive assessment should include standardized measures for both conditions (e.g., ADOS-2 for autism, Conners-3 or SNAP-IV for ADHD) administered by clinicians experienced in co-occurring neurodevelopmental conditions.
In Ontario, many of the province's autism diagnostic hubs now routinely screen for ADHD as part of the autism assessment process. However, waitlists for comprehensive dual assessments can extend beyond 18 months in some regions.
Medication for ADHD symptoms (stimulants and non-stimulants) is generally effective in autistic individuals, though response rates are somewhat lower and side effects may be more pronounced than in ADHD alone. A 2019 meta-analysis by Rodrigues et al. found that methylphenidate reduced ADHD symptoms in autistic children with a moderate effect size, but adverse effects (irritability, appetite loss) occurred at higher rates.
Behavioural interventions should address both conditions simultaneously. ABA-based interventions can incorporate ADHD-specific strategies such as organizational supports, task chunking, and reinforcement schedules designed for the shorter attention spans typical of ADHD. Occupational therapy focusing on executive function and self-regulation benefits both conditions.
Ontario's OAP funds clinical services that can address both autism and ADHD features. When developing a child's individualized service plan, families should ensure that ADHD-related goals (organization, attention, impulse control) are included alongside autism-specific goals.
Rommelse et al.
Shared heritability of attention-deficit/hyperactivity disorder and autism spectrum disorder. European Child & Adolescent Psychiatry, 2010; 19(3):281-295
Leitner, Y.
The co-occurrence of autism and attention deficit hyperactivity disorder in children. Frontiers in Human Neuroscience, 2014; 8:268
Rodrigues et al.
Pharmacological interventions for ADHD symptoms in autism spectrum disorders: meta-analysis. J Child Psychol Psychiatry, 2019; 60(7):706-722
Commitment to Accuracy: Our data is verified against official government reports (FAO, MCCSS), peer-reviewed scientific literature, and accessible public records. Last updated: March 24, 2026.
Verified Facts
1 in 50, According to the 2019 Canadian Health Survey on Children and Youth, about children and youth aged 1 to 17 in Canada had an autism diagnosis
88,175, children are registered in the Ontario Autism Program
WHO recommends accessible, community-based early interventions for children with autism — timely evidence-based psychosocial interventions improve communication and social engagement
23.4%, Only 20,666 children have active funding agreements () — less than one in four