This paper reviews the theory and historical developments that made it possible for the world's least affluent citizens to obtain the benefits of modern pharmaceutical therapy at affordable prices. Considered in turn are the theory of differential prices, the reasons why differential pricing was not widely practiced by pharmaceutical companies selling patented medicines; how low prices eventually became available, with emphasis on AIDS anti-retrovirals; and the consequences of low prices in the least developed nations for the creation of new and more effective medicines.
Scherer, F.M. "Patents, Monopoly Power, and the Pricing of Pharmaceuticals in Low-Income Nations." HKS Faculty Research Working Paper Series RWP13-029, September 2013.