If these questions have an answer, it is that addiction is not a simple matter of chemical and receptor. Habit, ritual, social context and the means of delivery all affect how the brain processes a drug and how we experience it. As a result, drug research is replete with paradox. Charles Schuster, a  behavioral pharmacologist, demonstrated that if you pair a stimulus (such as a colored light) with the administration of morphine, a test animal may later respond to the stimulus alone as if it were getting the drug. Conversely, Schuster found that presenting methadone in an unexpected flavor of Kool-Aid causes some addicts to act as if they have been deprived of the drug. Just as context makes a drug seem to be present, context can make it seem to be absent.