Classical conditioning is central to the process of drug addiction. Addiction treatment often focuses on the management of craving. Craving, or the urge to use the problem drug, can be very strong and frequently leads to relapses in people striving for sobriety. Craving is triggered by cues, both external and internal, via the process of classical conditioning. In other words, the person encounters a reminder of drug use (such as drug paraphernalia or the bar where the person used to drink) and the association stimulates craving. This is basically the same conditioning process Pavlov noticed with his dogs. External cues include environmental factors (people, places, and things). Internal cues include emotions, thought, or physical sensations that previously led to drug use.