(SLA-057) Two Decades of ADHD Diagnosis Trends in British Columbia: A Population-Based Study

Background: Understanding the age- and sex-specific shifts in ADHD diagnoses can help anticipate future health system needs.

Objectives: To examine the impact of DSM-5 diagnostic criteria changes and the COVID-19 pandemic on the incidence of ADHD diagnoses in British Columbia (BC), Canada, by age and sex.

Methods: This population-based retrospective cohort study utilized linked administrative data from 2003 to 2023 in BC. Four age groups were analyzed: preschool (3-5), elementary school (6-12), high school (13-17), and young adult (18-29). For each age group, yearly period prevalence and incidence of ADHD diagnoses were calculated and stratified by sex. Interrupted time series analyses were employed to assess trends in incident diagnoses of ADHD following DSM-5 updates in 2013 and the COVID-19 pandemic in 2020, with sex included as an effect modifier.

Results: From 2003 to 2023, among 3,655,001 BC residents aged 3 to 29, ADHD prevalence was lowest among preschool boys (0.5% to 1.4%) and girls (0.1% to 0.5%). Prevalence peaked in boys in elementary (4.0% to 9.5%) and high school (3.5% to 8.9%), and then declined in young men (0.5% to 4.3%). In contrast, ADHD prevalence in high-school girls (1.0% to 6.6%) and young women (0.3% to 5.7%) surpassed that of elementary-school girls (1.2% to 4.4%).
Over the study period, 110,874 men and 74,264 women were diagnosed with ADHD among 2,743,914 ADHD-naïve residents (50.2% men). Incidence rose across all age and sex groups, peaking in elementary-school boys (2013 to 2023: 128.0 to 346.2 per 10,000). DSM-5 accelerated annual incident ADHD diagnoses by 9.8 (95% CI: 7.2-12.3) per 10,000 in elementary-school boys and 3.5 (95% CI: 1.0-6.0) in girls. High-school boys had an additional 7.8 (95% CI: 5.8-9.9) and girls 6.7 (95% CI: 4.6-8.7) per 10,000 diagnosed annually. Post-COVID, incident ADHD diagnoses surged in 2021 by 107.3 (95% CI: 95.8-118.7) per 10,000 high-school girls and 123.1(95% CI: 115.9-130.2) for young women, with continued increases thereafter. The trends shifted peak incidence for women from elementary school to high school and young adulthood, reaching approximately 200 per 10,000 annually.

Conclusions: Over the past two decades, ADHD prevalence and incidence have risen significantly among children and young adults in BC, Canada. The adoption of DSM-5 criteria in 2013 accelerated ADHD incidence, most prominently among children and adolescents aged 6 to 17. The COVID-19 pandemic further amplified the upward trends, particularly with ADHD incidence skyrocketing among high school girls and young women, surpassing the incidence observed in same-aged men post-pandemic.