What follows might not be a new idea, but it happened to pop into my head last week when I was in the process of preparing a lecture on drug addiction. If it isn't new, then please let me know where you have read this idea before, as I would like to have that as a reference.

My(?) idea is based on some standard introductory psychology fare: Variable ratio (VR) schedules of reinforcement. In a VR schedule, a reinforcer is delivered after some random number of responses. A casino slot machine delivers rewards according to this schedule. VR schedules are notable for producing the highest rate of responding and the greatest resistance to extinction. There is a common idea that gambling owes some of its addictive potential to the fact that games of chance usually employ a VR schedule of reinforcement.

So what happens when you buy street drugs? You never know what you are going to get, that's what. If I were to head out and try to buy some heroin right now I would not know with any amount of certainty whether the drug I would get would be cut with 20%, 50%, or more filler. The result of my purchase would be a variable chance that I would get as high as I desired to get upon making my purchase. Accordingly, street drugs have a VR schedule of reinforcement: You only get very high on a street drug after some random number of purchases. The point of this discussion is that the addictive potential of a drug is possibly heightened by making it illegal: Its illegality produces unpredictable doses, thus unpredictable doses set up a VR schedule of reinforcement, and that VR schedule produces a behavioral response that is robust and difficult to extinguish. If this assessment is correct, then making a drug legal might reduce its addictive potential. Just a thought.