Substance Use and Addiction

Substance use and addiction refers to the substance-related disorders, a group of conditions arising from the use of alcohol, tobacco, and other psychoactive substances in which use becomes compulsive and persists despite harm. These conditions are commonly encountered in primary care and are increasingly framed as chronic, relapsing disorders of brain reward and self-regulation rather than failures of will.

Definition

Substance-related disorders are characterized by a pattern of use of a psychoactive substance that leads to clinically significant impairment or distress, with features that may include impaired control over use, continued use despite harm, increasing salience of the substance, tolerance, and withdrawal; addiction denotes the more severe end of this spectrum, marked by compulsive use and loss of control.

Scope

The entry covers the concept of substance-related and addictive disorders as defined in standard classifications, the distinction between use, harmful use, and dependence/addiction, hypothesized mechanisms, and population burden. It treats the topic as a reference entry within the family-medicine mental-health area and does not provide screening tools, dosing, or individualized treatment guidance.

Core questions

• How do substance use, harmful use, and addiction differ?
• What neurobiological changes characterize the transition to addiction?
• Why is addiction described as a chronic, relapsing disorder?

Key concepts

• Psychoactive substances
• Tolerance and withdrawal
• Impaired control and compulsive use
• Reward, motivation, and executive-control circuitry
• Craving and relapse
• Substance use disorder severity spectrum
• Brain disease model of addiction

Mechanisms

The dominant contemporary account frames addiction as a disorder of brain circuits governing reward, motivation, memory, and executive control. Repeated exposure to a substance is described as producing neuroadaptations that heighten the incentive value of the substance and associated cues, blunt sensitivity to natural rewards, and weaken prefrontal regulatory control, yielding craving, compulsive use, and vulnerability to relapse. Genetic predisposition, developmental timing, and environment interact to influence who develops these changes.

Clinical relevance

Substance-related disorders are common in primary care, frequently co-occur with depression, anxiety, and other psychiatric conditions, and contribute to a wide range of physical health problems. This entry describes the clinical concept and the evidence base for understanding it as reference material; it is not a screening instrument and is not a basis for diagnosing or treating an individual patient.

Epidemiology

Substance-use disorders affect a large number of people worldwide and contribute substantially to global disability and premature death, with alcohol and tobacco accounting for much of the attributable burden alongside illicit and prescription drugs. Burden and patterns of use vary markedly by region, substance, age, and sex, and the Global Burden of Disease studies track these differences over time.

Evidence & guidelines

These conditions are defined in the DSM-5, which combined earlier abuse and dependence categories into a single substance use disorder measured on a severity continuum, and in the ICD-11 (disorders due to substance use and addictive behaviours, codes 6C40-6C4Z), which also introduced a category for certain behavioural addictions. Authoritative reviews summarize the neurobiology of addiction, and the Global Burden of Disease studies quantify population impact. Specific management recommendations are issued by national bodies and lie outside this reference entry.

History

Habitual intoxication has been described for centuries, but the modern concept of substance-related disorders developed through twentieth-century medicine and psychiatry, moving from moral framings toward disease models. The DSM-5 unified abuse and dependence into a graded substance use disorder, the ICD-11 reorganized the category and recognized behavioural addictions, and neuroscience increasingly characterized addiction as a chronic disorder of brain reward and control systems.

Debates

Is addiction best understood as a brain disease?

The brain-disease model emphasizes neuroadaptations underlying compulsive use, but critics argue it can understate the roles of choice, social context, and recovery; the framing influences how responsibility, stigma, and policy are approached.

Should behavioural addictions be classified alongside substance disorders?

The ICD-11's inclusion of certain behavioural addictions extended the category beyond psychoactive substances, raising ongoing discussion about where the boundaries of addiction lie.

Seminal works

• volkow-2016
• vos-2022

Frequently asked questions

What is the difference between substance use and addiction?

Use refers to taking a substance, which may be occasional and without disorder; addiction is the severe end of a spectrum of substance-related disorder, marked by impaired control, compulsive use, and continued use despite harm.

Why is addiction called a chronic, relapsing disorder?

Because the neuroadaptations associated with addiction can persist after use stops, leaving lasting vulnerability to craving and relapse, which is why it is described as chronic and relapsing rather than acutely curable.