In this essay I examine the Rational Theory of Addiction proposed by Becker and Murphy in 1988. Their theory is an extension of rational choice theory to explain and predict aspects of addiction. Becker and Murphy conceive of addiction as a process of deciding to use (or abstaining from use) based on a rationally well-informed decision that consumption (or non-consumption of) the drug will maximize benefit over costs. I propose formal diagnostic conditions for the term 'addict' according to RTA. I then show how the theory has explanatory deficits in differentiating between two kinds of addicts (willing and unwilling addicts).