The
iron law of prohibition is a term coined by
Richard Cowan in 1986 which posits that as law enforcement becomes more intense, the potency of prohibited substances increases. Cowan put it this way: "the harder the enforcement, the harder the drugs." This law is an application of the
Alchian–Allen effect; Libertarian judge
James P. Gray calls the law the "
cardinal rule of prohibition", and notes that is a powerful tool for the
legalization of drugs. It is based on the premise that when drugs or alcohol are prohibited, they will be produced in
black markets in more concentrated and powerful forms, because these more potent forms offer better efficiency in the business model—they take up less space in storage, less weight in transportation, and they sell for more money. Economist
Mark Thornton writes that the iron law of prohibition undermines the argument in favor of prohibition, because the higher potency forms are less safe for the consumer.