Patterns of antidiabetic medicine supply across hospital levels during China’s post-2015 hierarchical healthcare reform period: a longitudinal study in Shanghai, 2016–2024

China introduced hierarchical diagnosis and treatment in 2015 to strengthen lower-level care and encourage routine chronic disease management outside tertiary hospitals. Diabetes requires continuous pharmacotherapy, making medicine supply across hospital levels a relevant supply-side indicator of chronic disease care. This study examined procurement-derived antidiabetic medicine patterns in Shanghai during the post-2015 reform period and whether they were consistent with the functional differentiation expected under hierarchical care. We conducted a longitudinal observational study using monthly public-sector procurement records for antidiabetic medicines in Shanghai from 2016 to 2024. Medicines were standardised using the WHO ATC/DDD methodology. We examined defined daily doses (DDDs), DDDs per 1,000 inhabitants per day (DID), defined daily cost (DDC), hospital-level distributions of volume and expenditure, ATC4-based therapeutic structural differentiation, diffusion of newer antidiabetic agents, and product-month-hospital-level regression models with hospital-level category and calendar-month fixed effects. Adjusted models controlled for reimbursement status, essential-medicine status, newer-agent status and injectable formulation. Total antidiabetic medicine volume increased from 427.8 million DDDs in 2016 to 614.2 million in 2024, and DID rose from 48.44 to 67.84 DDDs per 1,000 inhabitants per day. DDC declined from 3.94 to 3.21 CNY per DDD. Primary-level hospitals accounted for 60.7% of DDDs in 2016 and 64.4% in 2024; the secondary-hospital share declined from 24.5% to 19.0%, while the tertiary-hospital share changed from 14.8% to 16.6%. In 2024, DDC was 2.36, 4.38 and 5.17 CNY/DDD in primary, secondary and tertiary hospitals, respectively. The primary-tertiary ATC4 dissimilarity index increased from 0.226 to 0.281. Newer agents reached 28.5%, 37.0% and 44.1% of within-level DDDs in primary, secondary and tertiary hospitals, respectively. At the product-month level, adjusted models showed a stronger annual DDDs trend in tertiary hospitals than in lower-level hospitals, while DDC declined across all three levels. During 2016–2024, antidiabetic medicine supply in Shanghai was characterised by a large and increasing primary-care share of routine volume, declining daily treatment cost, persistent therapeutic differentiation across hospital levels, and diffusion of newer agents across all levels with the highest intensity in tertiary care. These supply-side patterns were broadly compatible with the functional division expected under hierarchical chronic disease care, but they should not be interpreted as causal effects of the 2015 reform. Policy efforts should prioritise reliable and continuous access to essential and commonly used medicines in primary care, clarify the intermediary role of secondary hospitals in chronic disease management, and develop shared-care arrangements to facilitate clinically appropriate access to newer therapies across levels of care.