The Science of Drug Abuse and Addiction

What is drug addiction?

Addiction is defined as a chronic, relapsing brain disease that is characterized by compulsive drug seeking and use, despite harmful consequences. It is considered a brain disease because drugs change the brain; they change its structure and how it works. These brain changes can be long lasting and can lead to many harmful, often self-destructive, behaviors.

Why study drug abuse and addiction?

Abuse of and addiction to alcohol, nicotine, and illegal substances cost Americans upwards of half a trillion dollars a year (the combined medical, economic, criminal, and social impact). Every year, the abuse of illicit drugs and alcohol contributes to the death of more than 100,000 Americans, while tobacco is linked to an estimated 440,000 deaths per year.

How are drug disorders categorized?

The Diagnostic and Statistical Manual of Mental Disorders (DSM) is a diagnostic manual used by clinicians, that contains descriptions and symptoms of all mental disorders classified by the American Psychiatric Association. The DSM uses the term “substance use disorders” to characterize illnesses associated with drug use. There are two broad categories: substance abuse and substance dependence. Both are associated with a maladaptive pattern of substance use that leads to clinically significant impairment. Drug abuse includes such symptoms as:

  • failure to fulfill major role obligations;
  • legal problems;
  • use in situations that are physically hazardous; and
  • continued use despite persistent social or interpersonal problems.

The term dependence includes such symptoms as:

  • drug taking in larger amounts than intended;
  • inability to cut down on drug use;
  • a great deal of time spent in activities necessary to obtain the drug; and
  • continued use despite knowledge of health or social problems caused by the drug.

Dependence may or may not include “physical dependence,” defined by withdrawal symptoms when drug use is abruptly ceased, and tolerance, the need for more drug to achieve a desired effect. The DSM term “dependence” is what NIDA refers to as “addiction.”

What is the difference between “physical dependence,” dependence, and addiction?

Physical dependence is not equivalent to dependence or addiction and may occur with the chronic use of any substance, legal or illegal, even when taken as prescribed. It occurs because the body naturally adapts to chronic exposure to a substance (e.g., caffeine or a prescription drug), and when that substance is taken away, symptoms can emerge while the body readjusts to the loss of the substance. Physical dependence can lead to craving for the drug to relieve the withdrawal symptoms. Drug dependence and addiction refer to drug or substance use disorders, which may include physical dependence but must also meet additional criteria.

How does NIDA use the terms drug abuse and addiction?

NIDA defines any illicit use of a substance as drug abuse; this includes the non-medical use of prescription drugs. NIDA defines addiction as a chronic, relapsing disease characterized by compulsive drug seeking and use despite harmful consequences as well as neurochemical and molecular changes in the brain. NIDA’s use of the term addiction corresponds roughly to the DSM definition of dependence. The DSM does not use the term addiction.

How do drugs work in the brain to produce pleasure?

Nearly all drugs of abuse 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 feelings of pleasure. The over-stimulation of this system, which rewards our natural behaviors, produces the euphoric effects sought by people who abuse drugs and teaches them to repeat the behavior.

Is drug abuse a voluntary behavior?

The initial decision to take drugs is mostly voluntary. However, when addiction takes over, a person’s ability to exert self-control can become seriously impaired. Brain-imaging studies from drug-addicted individuals show physical changes in areas of the brain that are critical for judgment, decision making, learning and 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 an addicted person.

Can addiction be treated successfully?

Yes. Addiction is a treatable, chronic disease that can be managed successfully. Research shows that combining behavioral therapy with medications, where available, is the best way to ensure success for most patients. Treatment approaches must be tailored to address each patient’s drug abuse patterns and drug-related medical, psychiatric, and social problems.

Does relapse to drug abuse mean treatment has failed?

No. The chronic nature of the disease means that relapsing to drug abuse is not only possible but also likely. Relapse rates are similar to those for other well-characterized chronic medical illnesses, such as diabetes, hypertension, and asthma, which also have both physiological and behavioral components. Treatment of chronic diseases involves changing deeply embedded behaviors. For the addicted patient, lapses back to drug abuse indicate that treatment needs to be reinstated or adjusted or that alternate treatment is needed.

Comparison of Relapse Rates Between Drug Addiction and Other Chronic Illnesses

Relapse rates for drug-addicted patients are compared with those suffering from diabetes, 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.


Source: McLellan et al., JAMA, 284:1689-1695, 2000.