INTRODUCTION: In India, public sector patients purchase drugs from private pharmacies instead of obtaining them for free from public pharmacies-a phenomenon we call public patient forwarding to private pharmacies. This behaviour results in substantial financial hardship. We examine whether low public drug stocks, patient preferences for private drugs or the presence of private pharmacies nearby explain this behaviour. METHODS: We collected cross-sectional data from 7567 households, 523 health facilities and 1036 private pharmacies in Odisha, India. We linked 917 outpatient visits to facilities based on patient reports and linked public facilities to the nearest private pharmacy using Global Positioning System coordinates. We used ordinary least squares regression to assess whether the behaviour of facilities and patients was associated with drug stocks and pharmacy proximity, and whether patient satisfaction was associated with private drug purchases. RESULTS: Among public patients prescribed drugs, more than 70% purchased private drugs. In hospitals, for each 10% increase in drug stocks, 4.8% fewer patients purchased private drugs (p=0.047). In primary facilities, the same share of patients purchased private drugs across stock levels. Regardless of facility level, when more than 75% of drugs were in stock, 60% or more of patients still obtained drugs from the private sector. Patients were more likely to purchase private drugs when private pharmacies were near public facilities, but were not more satisfied with their visit when they obtained private drugs. CONCLUSION: The results suggest that private pharmacies are both secondary and complementary suppliers of drugs for hospitals, but may act more like substitutes for primary facilities, consistent with evidence that private pharmacies provide advice and other services akin to primary care in Odisha. Improving public facility drug stocks alone is unlikely to fully address drug-driven financial hardship in India. Provider prescribing practices should be investigated to identify additional policy options.