We consider how to conduct cost-effectiveness analysis when the social cost of a resource differs from the posted price. From the social perspective, the true cost of a medical intervention is the marginal cost of delivering another unit of a treatment, plus the social cost (deadweight loss) of raising the revenue to fund the treatment. We focus on pharmaceutical prices, which have high markups over marginal cost due to the monopoly power granted to pharmaceutical companies when drugs are under patent. We find that the social cost of a branded drug is approximately one-half the market price when the treatment is paid for by a public insurance plan and one-third the market price for mandated coverage by private insurance. We illustrate the importance of correctly accounting for social costs using two examples: coverage for statin drugs and approval for a drug to treat kidney cancer (sorafenib). In each case, we show that the correct social perspective for cost-effectiveness analysis would be more lenient than researcher recommendations.