Abstract
BACKGROUND: In December 2019, a nationwide registration system with strict distribution controls for extended-release methylphenidate (ER-MPH) was introduced to prevent inappropriate use while maintaining treatment access for patients with attention deficit hyperactivity disorder (ADHD). However, its impact on prescription patterns remains unclear. METHODS: We conducted an observational study using Japan’s National Database of Health Insurance Claims from 2016 to 2022. ER-MPH prescription volumes were calculated as defined daily doses per 1,000 individuals. Interrupted time series (ITS) analysis was performed to assess the impact of the 2019 distribution-control policy across age and sex groups. We additionally examined whether regional differences in prescription trends could be explained by access to care by assessing the correlation between ER-MPH prescription volumes and the distribution of board-certified pediatricians using Pearson’s correlation coefficients. RESULTS: ER-MPH prescriptions continued to increase after the 2019 policy implementation, but ITS analysis revealed a substantial slowdown in the growth rate. Prescriptions declined immediately by 7% at policy implementation (level change incidence rate ratio [IRR] = 0.93, 95% confidence interval [CI]: 0.89–0.96), and the annual growth rate slowed from 27% pre-policy (IRR = 1.27, 95% CI: 1.25–1.28) to 9% post-policy (IRR = 1.09, 95% CI: 1.08–1.10) (slope change IRR = 0.86, 95% CI: 0.85–0.87). Age-stratified analyses revealed differential impacts: individuals aged < 20 years showed a 47% immediate decline (IRR = 0.53, 95% CI: 0.42–0.68) with nearly flat subsequent growth, while adults aged ≥ 20 years had only a 19% reduction (IRR = 0.81, 95% CI: 0.79–0.84) and continued slower growth. Sex-specific analyses also showed attenuated growth. The correlation between prescription volumes and pediatrician distribution was weak, indicating no substantial relationship. CONCLUSIONS: The 2019 distribution-control measures markedly attenuated the existing upward trend, especially among individuals aged < 20 years. Although prescription patterns differed by age and sex, these differences alone did not fully explain the overall attenuation, and regional variation showed only weak correlations with pediatrician distribution. These findings suggest that additional factors such as psychiatrist availability and broader healthcare system characteristics may also have influenced prescribing trends, underscoring the need for further investigation.