An overpowering desire or need (compulsion) tocontinue taking the drug and obtain it by any means. Drug addicts are habitual drug users who continue to take a drug despite its adverse effects on their health and social life. Addictive drugs stimulate brain mechanisms of reinforcement responsible for positive reinforcement. Video: the mind second edition: brain mechanisms of pleasure and behavior. Drugs that lead to addiction must reinforce the behavior. Positive reinforcement: positive reinforcement increases the frequency of behavior because it is regularly followed by an appetitive stimulus. Negative reinforcement: negative reinforcement increases the frequency of behavior because of the removal of an aversive stimulus. Ex: a rat will press a lever (the behavior) to prevent the occurrence of a foot shock (the aversive stimulus): negative reinforcement is not the same as punishment. Negative reinforcement increases frequency of behavior, ex: if i take another shot, my withdrawal symptoms will disappear.