Addiction is a state characterized by compulsive engagement in rewarding stimuli, despite adverse consequences; it can be thought of as a disease or biological process leading to such behaviors. The two properties that characterize all addictive stimuli are that they are (positively) reinforcing (i.e., they increase the likelihood that a person will seek repeated exposure to them) and intrinsically rewarding (i.e., they activate the brain’s “reward pathways”, and are therefore perceived as being something positive or desirable). ΔFosB, a gene transcription factor, is now known to be a critical component and common factor in the development of virtually all forms of behavioral and drug addictions. Addiction exacts a high toll on individuals and society as a whole through the direct adverse effects of drugs and associated healthcare costs, the functional consequences of altered neuroplasticity in the brain, and the loss of productivity. Classic hallmarks of addiction include impaired control over substances or behavior, preoccupation with substance or behavior, continued use despite consequences, and denial. Habits and patterns associated with addiction are typically characterized by immediate gratification (short-term reward), coupled with delayed deleterious effects (long-term costs). Potential addictions can include, but are not limited to, exercise addiction, food addiction, drug addiction, computer addiction, sex addiction and gambling addiction. Currently, only substance addictions and gambling addiction are recognized by the , which uses physical dependence and the associated withdrawal syndrome to identify an addictive state. Physical dependence occurs when the body has adjusted by incorporating the substance into its “normal” functioning – i.e., attains homeostasis – and therefore physical withdrawal symptoms occur upon cessation of use. Tolerance is the process by which the body continually adapts to the substance and requires increasingly larger amounts to achieve the original effects. Withdrawal refers to physical and psychological symptoms experienced when reducing or discontinuing a substance that the body has become dependent on. Symptoms of withdrawal generally include but are not limited to anxiety, irritability, intense cravings for the substance, nausea, hallucinations, headaches, cold sweats, and tremors.