Addiction

Did You Know?

• The DSM-5 discourages the term drug addiction due to its uncertain definition and negative connotation, preferring substance use disorder.
• The most immediate danger of addiction is overdose, which for opioids and other sedatives acts by suppressing breathing.
• Injecting drug use carries a risk of blood-borne infection, including HIV and hepatitis C.

Causes

Genetic and environmental risk factors each account for roughly half of an individual's risk for developing an addiction. Even in those with low genetic risk, sufficiently high doses of an addictive drug over weeks to months can result in addiction. Twin and adoption studies estimate the heritability of alcohol use disorder at about 50%, with comparable figures across other substances. This risk is polygenic, reflecting the combined small effects of many common variants rather than any single gene.

Genome-wide association studies have begun to map this architecture, distinguishing loci associated with a broad general liability to addiction across substances from those conferring risk for a specific drug. Environmental risk factors include early aggressive behavior, lack of parental supervision, peer substance use, availability of substances, and poverty, as listed by the National Institute on Drug Abuse. These factors interact with an individual's genetic composition to increase or decrease vulnerability.

Mechanisms

Addiction is a condition that arises from repeatedly engaging with a rewarding stimulus, which permanently alters the brain's reward, stress, and self-control systems. This process unfolds in a repeating three-phase cycle. In the binge/intoxication phase, dopamine signals in the basal ganglia make the drug and its related cues highly compelling. During withdrawal/negative affect, stress circuits in the extended amygdala become hyperactive, and normal pleasures feel dull, shifting the motivation for use from seeking reward to finding relief.

In the preoccupation/anticipation phase, weakened control from the prefrontal cortex leaves cravings unchecked, increasing the risk of relapse. Each phase involves lasting changes in gene activity and how neurons connect. In animal studies, repeated drug use builds up a protein called ΔFosB in reward-related neurons, which boosts drug-taking and reduces sensitivity to negative outcomes. Most addictive drugs reinforce behavior through dopamine in the nucleus accumbens, a pathway also triggered by natural rewards like food or sex.

Addiction impairs cognitive control, especially the ability to inhibit behavior, while environmental cues and conditioned responses increasingly drive actions.

Theories and models

One major explanation for addiction is the brain disease model, which highlights drug exposure as the key environmental risk. However, some researchers, including Marc Lewis, have challenged this view, arguing that the brain changes seen in addiction are actually a form of learning. In 2018, Lewis helped form the Addiction Theory Network to promote an alternative view based on choice, learning, and social context. Another perspective, psychoanalytic theory, sees addiction as a defense against feelings of hopelessness and helplessness, often linked to adverse childhood experiences.

In this view, the substance offers temporary relief and a sense of control. Psychological factors also play a role, including learning and conditioning, impulsivity, sensitivity to rewards, and using substances to cope with negative moods or trauma. Conditioning models show that environmental cues can trigger cravings and relapse even after long periods of abstinence. Personality theories connect certain traits or thinking patterns to addiction risk.

Proposed models include affect dysregulation, reinforcement sensitivity theory, and an impulsivity model focused on reward sensitization. These psychological processes interact with biological and social vulnerabilities, each reinforcing the others.

Society and culture

Addiction carries substantial social and economic consequences and is among the more heavily stigmatized health conditions, with negative attitudes documented among clinicians and the general public. A systematic review of health professionals in Western countries found negative attitudes common, associated with poorer communication, less patient involvement in care decisions, and reduced treatment engagement. A later US systematic review reported similar findings among clinicians and trainees, noting that some educational and contact-based interventions reduced measured stigma, though studies were few and varied.

The arts are used in advocacy and public education, with artists, particularly those with lived experience, working to reduce stigma and reframe addiction as a treatable health condition rather than a moral failing. Addiction imposes substantial financial and human costs from direct drug effects, healthcare costs, long-term complications, lost productivity, accidents, suicides, homicides, and incarceration. In the United States, an estimated 69,973 people died of drug overdose in 2025, down almost 14% from 81,313 in 2024.

Access to treatment is limited worldwide, with the proportion of people with a substance use disorder in contact with treatment services ranging from under 1% to no more than 35% among countries reporting to the World Health Organization.