External Referencing and Pharmaceutical Price Negotiation

External referencing (ER) imposes a price cap for pharmaceuticals based on prices of identical products in foreign countries. Suppose a foreign country (F) negotiates prices with a pharmaceutical firm while a home country (H) can either negotiate independently or implement ER based on the foreign price. We show that country H always prefers ER if (i) it can condition ER on the drug being subsidized in the foreign country and (ii) copayments are higher in H than in F. H's preference is reinforced when the difference between country copayments is large and/or H's population is small. External referencing by H always harms F if (ii) holds, but less so if (i) holds