Addiction is defined as a chronic, relapsing disorder characterized by compulsive drug seeking, continued use despite harmful consequences, and long-lasting changes in the brain. It is considered both a complex brain disorder and a mental illness. Addiction is the most severe form of a full spectrum of substance use disorders, and is a medical illness caused by repeated misuse of a substance or substances. The symptoms associated with a substance use disorder fall into four major groupings: impaired control, social impairment, risky use, and pharmacological criteria (i.e., tolerance and withdrawal). The diagnostic criteria are as follows: The substance is often taken in larger amounts or over a longer period than was intended. There is a persistent desire or unsuccessful effort to cut down or control use of the substance. A great deal of time is spent in activities necessary to obtain the substance, use the substance, or recover from its effects. Craving, or a strong desire or urge to use the substance, occurs. Recurrent use of the substance results in a failure to fulfill major role obligations at work, school, or home. Use of the substance continues despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of its use. Important social, occupational, or recreational activities are given up or reduced because of use of the substance. Use of the substance is recurrent in situations in which it is physically hazardous. Use of the substance is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance. Tolerance, as defined by either of the following: A need for markedly increased amounts of the substance to achieve intoxication or desired effect A markedly diminished effect with continued use of the same amount of the substance. Withdrawal, as manifested by either of the following: The characteristic withdrawal syndrome for that substance (as specified in the DSM-5 for each substance). The use of a substance (or a closely related substance) to relieve or avoid withdrawal symptoms. What is drug use, misuse, and addiction? Drug use refers to any scope of use of illegal drugs: heroin use, cocaine use, tobacco use. Drug misuse is used to distinguish improper or unhealthy use from use of a medication as prescribed or alcohol in moderation. These include the repeated use of drugs to produce pleasure, alleviate stress, and/or alter or avoid reality. It also includes using prescription drugs in ways other than prescribed or using someone else’s prescription. Addiction refers to substance use disorders at the severe end of the spectrum and is characterized by a person’s inability to control the impulse to use drugs even when there are negative consequences. These behavioral changes are also accompanied by changes in brain function, especially in the brain’s natural inhibition and reward centers. How do drugs work in the brain to produce pleasure? Nearly all addictive drugs directly or indirectly target the brain’s reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that regulate movement, emotion, cognition, motivation, and reinforcement of rewarding behaviors. When activated at normal levels, this system rewards our natural behaviors. Overstimulating the system with drugs, however, produces effects which strongly reinforce the behavior of drug use, teaching the person to repeat it. Is drug use or misuse a voluntary behavior? The initial decision to take drugs is generally voluntary. However, with continued use, a person’s ability to exert self-control can become seriously impaired. Brain imaging studies from people addicted to drugs show physical changes in areas of the brain that are critical for judgment, decision-making, learning, memory, and behavior control. Scientists believe that these changes alter the way the brain works and may help explain the compulsive and destructive behaviors of a person who becomes addicted. Can addiction be treated successfully? Yes. Addiction is a treatable, chronic disorder that can be managed successfully. The combination of medications and behavioral interventions to treat a substance use disorder is known as medication-assisted treatment. Treatment approaches must be tailored to address each patient’s drug use patterns and drug-related medical, psychiatric, environmental, and social problems. Relapse rates for patients with substance use disorders are compared with those suffering from hypertension and asthma. Relapse is common and similar across these illnesses (as is adherence to medication). Thus, drug addiction should be treated like any other chronic illness, with relapse serving as a trigger for renewed intervention.