Abstract
BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) is one of the most commonly diagnosed mental disorders in children. For many patients, treatment involves long-term medication in order to reduce symptoms, regulate behaviour, and, hopefully, improve school performance and achievement. However, there is little to no evidence to support a long-term effect on the latter complex outcomes. METHODS: We utilize a target trial framework to emulate a pretest-posttest control group design and estimate the intention-to-treat effect of ADHD medication on national test scores in children diagnosed with ADHD born between 2000 and 2007 in Norway. The data were obtained through linkage of Norwegian registries (NorPD, Norwegian Prescription Database; NPR, Norwegian Patient Registry; KUHR, Database for Control and Payment of Health Reimbursement; SSB, Statistics Norway; MBRN, Medical Birth Registry of Norway). RESULTS: The resulting analytic sample size consisted of 8548 children diagnosed with ADHD, with about 9% missingness in their grade eight national test scores. We find that initiating ADHD medication had a slight positive average effect on national test scores for all three domains: English, numeracy, and reading [standardized mean differences: 0.037 (95% compatibility interval (CI95), -0.003; 0.076), 0.063 (CI95, 0.016; 0.111), 0.071 (CI95, 0.030; 0.111), respectively]. CONCLUSION: We conclude that the estimated long-term average effect of ADHD medication on learning, as measured by the Norwegian national tests, is not clinically relevant. Study strengths include the use of real-world data on ecologically valid and relevant outcomes and the robustness of results across model specifications. Limitations include possibility of unobserved confounding and lack of prescription data.