Abstinence is the best way to avoid drug addiction. But in many societies, drug use is the norm, not the exception, especially by youth. What keeps the majority of users from becoming addicted? How drugs are taken has something to do with it, according to pharmacology researchers at the University of Montreal. “Why do some drug users become addicts? The amount of drugs they take over time is one factor, but the speed with which the substance enters and exits the brain can be just as important,” explained Professor Anne-Noël Samaha, who supervised the study into how pharmacokinetic factors govern addiction.