A comprehensive Swedish study tracking nearly a quarter-million ADHD medication users over 14 years has revealed that while these medications consistently reduce risks of serious adverse outcomes, their protective effects are diminishing as prescription rates climb nationwide.
The population-based study, published in JAMA Psychiatry by researchers from the Karolinska Institutet in Stockholm and Indiana University, analyzed 247,420 Swedish individuals aged 4 to 64 years who used ADHD medications between 2006 and 2020. During this period, ADHD medication prevalence increased dramatically from 0.6% to 2.8%.
Consistent Protective Effects Across Multiple Outcomes
Using a self-controlled case series design with Swedish National Registry data, researchers compared rates of self-harm, unintentional injury, traffic crashes, and crime during medicated versus nonmedicated periods. The study population included 99,361 females (40.2%) and 148,059 males (59.8%).
ADHD medication use was consistently associated with lower risks across all measured outcomes:
- Self-harm: Incidence rate ratio (IRR) ranged from 0.77 (95% CI, 0.73-0.81) to 0.85 (95% CI, 0.82-0.88)
- Unintentional injury: IRR ranged from 0.87 (95% CI, 0.84-0.89) to 0.93 (95% CI, 0.91-0.95)
- Traffic crashes: IRR ranged from 0.71 (95% CI, 0.67-0.77) to 0.87 (95% CI, 0.83-0.91)
- Crime: IRR ranged from 0.73 (95% CI, 0.71-0.75) to 0.84 (95% CI, 0.82-0.85)
These protective associations held across different age groups, sexes, and time periods.
Weakening Benefits Over Time
Despite the consistent protective effects, the magnitude of these associations weakened over time as prescribing rates increased. The researchers stratified their analysis across three time intervals—2006 to 2010, 2011 to 2015, and 2016 to 2020—and found statistically significant trends (P for trend < .01) showing diminishing benefits, particularly for unintentional injury, traffic crashes, and crime.
"These results demonstrated that ADHD medications were consistently associated with reduced risks of several serious real-world outcomes, but these associations appear to weaken alongside shifts in the patient population, highlighting the need for ongoing review of treatment guidelines," the researchers wrote.
Implications for Clinical Practice
The study's findings raise important questions about the evolving landscape of ADHD treatment. Changes in age and sex distribution of individuals receiving ADHD medication did not fully explain the weakening trend for unintentional injury and traffic crashes, suggesting other factors may be at play.
The researchers emphasized that "these significant shifts highlight a critical question: do those receiving ADHD medication today benefit from the treatment in the same way as those who received it a decade ago?"
Growing Treatment Landscape
ADHD affects approximately 5.3% of youths and 2.5% of adults worldwide, making it the most prevalent neurodevelopmental disorder. The diagnosis of ADHD and prescription of ADHD medication has increased substantially worldwide over the last decade.
The study team urged clinicians to "regularly evaluate medication use in different patient populations" and noted that "understanding these evolving dynamics is essential for optimizing treatment strategies across diverse patient populations, as well as for informing treatment guidelines and recommendations for both children and adults."
While ADHD medications remain associated with reduced risk of several adverse real-world outcomes, the diminishing effect as prescribing expands highlights the need for ongoing evaluation of medication use and patient selection to ensure optimal therapeutic outcomes.
