As scientists and researchers learned more about alcoholism, its definition was revised and refined. Most people consider an alcoholic to be someone who drinks too much and cannot control his or her drinking. Alcoholism, however, does not merely refer to heavy drinking or getting drunk a certain number of times. The diagnosis of alcoholism applies only to those who show specific symptoms of addiction.

In 1992 Drs. Robert Morse and Daniel Flavin, writing for the Joint Committee of the National Council on Alcoholism and Drug Dependence and the American Society of Addiction Medicine ("The Definition of Alcoholism," Journal of the American Medical Association, 1992), defined alcoholism as:

[A] primary, chronic disease with genetic, psychosocial, and environmental factors influencing its development and manifestations. The disease is often progressive and fatal. It is characterized by impaired control over drinking, preoccupation with the drug alcohol, use of alcohol despite adverse consequences, and distortions in thinking, most notably denial. Each of these symptoms may be continuous or periodic.

"Primary" refers to alcoholism as a disease independent from any other psychological disease (for example, schizophrenia), rather than a symptom of some other underlying disease. "Adverse consequences" for an alcoholic can include physical illness (liver disease, withdrawal symptoms, etc.), psychological problems, interpersonal difficulties (such as marital problems or domestic violence), and problems at work.

This definition of alcoholism incorporated "denial" as a major concept for the first time. Denial includes a number of psychological maneuvers by the drinker to avoid the fact that alcohol is the cause of his or her problems. Family and friends may reinforce an alcoholic's denial by covering up his or her drinking (for example, calling an employer to say the alcoholic has the flu rather than a hangover). Such behavior is also known as enabling. In other words, the friends and family make excuses for the drinker and enable him or her to continue drinking as opposed to having to face the repercussions of his or her alcohol abuse. Denial is a major obstacle in recovery.

The Institute of Medicine (IOM) has defined addiction as a brain disease "manifested by a complex set of behaviors that are the result of genetic, biological, psychological, and environmental interactions."