*Names in bold indicate Presenter
This paper considers a number of apparent paradoxes of including 1. Purity. Heroin regularly travels in large shipments that are substantially impure, even though that increases the risks and costs of smuggling per pure gram of heroin. 2. Price and purity. Within individual markets there is a strong negative correlation between average purity and purity-adjusted price, even though the principal driver of purity-adjusted price is enforcement risk; higher enforcement risk should increase the incentives for more compact (i.e., higher purity) cocaine or heroin. 3. Price response to government intervention. The massive increase in enforcement intensity against sellers in the United States has been accompanied by a large and continued decline in the price of both cocaine and heroin. For each of these the paper offers potential explanatory factors rooted in a theory of the institutional and behavioral consequences of toughly enforced prohibition.