Drug dependence

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"drug dependence" OR "substance use disorder"

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Drug Dependence

Definition

Drug dependence is defined by the WHO as: "a state, psychic and sometimes also physical, resulting from the interaction between a living organism and a drug, characterized by behavioural and other responses that always include a compulsion to take the drug on a continuous or periodic basis in order to experience its psychic effects, and sometimes to avoid the discomfort of its absence."

A drug (WHO) is any substance that, when taken into a living organism, may modify one or more of its functions. Drug abuse refers to self-administration for non-medical reasons, in quantities and frequencies that impair functioning and cause social, physical, or emotional harm.

Park's Textbook of Preventive and Social Medicine, p. 936

Dependence vs. Addiction - A Critical Distinction

These two terms are often confused but represent distinct phenomena:

Feature	Physical Dependence	Addiction
Definition	Biological adaptation after chronic drug use	Compulsive, relapsing drug use despite negative consequences
Key features	Tolerance + Withdrawal	Loss of control, craving, drug-seeking behavior
Synonymous with addiction?	No	No
Can occur without the other?	Yes (e.g., patients on long-term opioids for pain)	Yes (relapse after successful withdrawal)

Tolerance: The need to use increasingly higher doses to achieve the same effect.
Withdrawal: Physical and/or psychological symptoms on abrupt drug cessation; may be life-threatening (e.g., convulsions with alcohol/benzodiazepines).
Addiction (psychological dependence): Compulsive use driven by cravings, often triggered by contextual cues, continuing despite negative consequences.

Notably, only a small fraction of users develop compulsive addiction - only 1 in 6 people who first use cocaine become addicted within 10 years, and very few patients receiving opioids for analgesia develop addiction. Conversely, relapse is common after withdrawal.

Katzung's Basic and Clinical Pharmacology (16th ed.), p. 906
Lippincott Illustrated Reviews: Pharmacology, p. 1542
Maudsley Deprescribing Guidelines

ICD-10 Classification of Dependence-Producing Drugs

ICD-10 recognizes the following psychoactive substances that may produce dependence:

Alcohol
Opioids
Cannabinoids
Sedatives or hypnotics
Cocaine
Other stimulants (including caffeine)
Hallucinogens
Tobacco
Volatile solvents
Other psychoactive substances and combinations

Park's Textbook of Preventive and Social Medicine, p. 937

Commonly abused substances classified into Stimulants, Hallucinogens, and Other Drugs of Abuse

Commonly abused substances - Lippincott Illustrated Reviews: Pharmacology

Profiles of Major Dependence-Producing Drugs

1. Amphetamines & Cocaine

Amphetamines: Synthetic, CNS stimulants structurally similar to adrenaline. Produce mood elevation, elation, increased alertness, and heightened energy ("superman drugs"). Cause psychic dependence, rapid and strong with large doses.
Cocaine: Derived from coca plant leaves. Potent CNS stimulant; produces no tolerance and no physical dependence or withdrawal symptoms per se. Cocaine produces intense but short-lived euphoria, leading to strong psychic/psychological dependence.

2. Opioids (Heroin, Morphine, Codeine, Methadone, Pethidine)

Heroin addiction is considered among the worst types: produces intense craving.
Strong psychic dependence develops early; tolerance develops rapidly, requiring escalating doses.
Produces both physical and psychological dependence with a defined withdrawal syndrome.

3. Barbiturates & Sedatives

Produce both physical and psychic dependence (craving, severe withdrawal). Addiction is among the most severe forms.

4. Cannabis (Marijuana, Hashish, Bhang, Ganja)

Most widely used drug globally.
Produces psychic dependence (not significant physical dependence in most users).
Effects: euphoria, altered perception of time/space, relaxation, paranoia; lasts 1-4 hours when smoked.

5. Alcohol

Pharmacologically a CNS depressant. Produces psychic dependence of varying degrees; physical dependence develops slowly.
Considered a disease agent causing cirrhosis, toxic psychosis, gastritis, pancreatitis, cardiomyopathy, and peripheral neuropathy. Associated with cancer (mouth, pharynx, larynx, oesophagus) and suicide/accidents.

6. Tobacco/Nicotine

Causes more deaths than all other psychoactive substances combined (~7 million premature deaths/year worldwide).
Strong psychic and physical dependence; nicotine withdrawal is well-characterized.

7. LSD (Lysergic Acid Diethylamide)

Potent psychotogenic agent; active at 100-250 µg orally.
No physical dependence; no withdrawal syndrome. No addiction liability in the traditional sense.
Effects: intense perceptual distortions, depersonalization, synesthesia.
Park's Textbook of Preventive and Social Medicine, pp. 937-940

Neurobiology: The Mesolimbic Dopamine System

The central mechanism of addiction involves the mesolimbic dopamine (reward) pathway:

Ventral Tegmental Area (VTA) dopamine neurons project to the nucleus accumbens, amygdala, hippocampus, and prefrontal cortex.
All addictive drugs increase dopamine release in the nucleus accumbens, either directly (cocaine, amphetamines) or indirectly (opioids, alcohol, nicotine, THC).
This dopamine surge encodes reward prediction error - the basis of reinforcement learning.
With chronic exposure, synaptic plasticity (LTP/LTD at glutamatergic synapses) in this circuit underlies tolerance, craving, and relapse.

Key processes:

Tolerance: Homeostatic downregulation of reward mechanisms - the brain suppresses its own endogenous reward in response to repeated drug stimulation.
Sensitization: Increased behavioral response (locomotor activity) to intermittent drug exposure - may reflect enhanced incentive salience.
Conditioned cues: Environmental cues associated with past drug use become powerful triggers for craving and relapse, even after withdrawal - mediated by synaptic plasticity in the VTA, nucleus accumbens, and prefrontal cortex.
Katzung's Basic and Clinical Pharmacology (16th ed.), pp. 906-910
Goodman & Gilman's Pharmacological Basis of Therapeutics

Host (Individual) Factors

Vulnerability to drug dependence is influenced by:

Age: Adolescents are particularly susceptible (developing brain, peer influence)
Mental health: Psychiatric comorbidities (depression, anxiety, PTSD) increase risk
Genetics: Heritable predisposition
Social environment: Peer pressure, family drug use, stress, poverty

Environmental / Agent Factors

Availability and accessibility of drugs
Price and legal status
Cultural and social norms
Marketing of alcohol and tobacco
Route of administration (intravenous > inhaled > oral in terms of addictive potential)

Complications of Drug Dependence

System	Effects
Medical	HIV/AIDS (IV drug use), hepatitis B/C, endocarditis, overdose, organ damage
Neurological	Toxic psychosis, neuropathy, seizures (withdrawal)
Psychiatric	Depression, anxiety, paranoia, psychosis
Social	Family breakdown, crime, loss of employment, homelessness
Economic	Loss of productivity, healthcare costs

Management / Treatment Principles

Treatment of drug dependence requires a multi-modal approach:

Detoxification - supervised withdrawal; medically managed for alcohol/benzodiazepines (risk of seizures, delirium tremens) and opioids
Pharmacotherapy:
- Opioid use disorder: methadone, buprenorphine (opioid substitution therapy), extended-release naltrexone
- Alcohol use disorder: disulfiram, naltrexone, acamprosate
- Nicotine: nicotine replacement therapy, varenicline, bupropion
Psychosocial interventions: Cognitive behavioral therapy (CBT), motivational interviewing, 12-step programs
Harm reduction: Needle exchange programs, naloxone distribution
Rehabilitation and relapse prevention

Approximately 80% of active drug users in the United States are not in treatment. Access to opioid substitution therapy remains a key public health gap.

Goldman-Cecil Medicine
Lippincott Illustrated Reviews: Pharmacology, p. 1542

Public Health & Prevention Strategies

Per WHO recommendations:

Regulate marketing of addictive substances (especially toward youth)
Restrict availability and raise prices through taxation
Implement drink-driving policies
Expand accessible treatment services
Screening and brief interventions in primary care
The SDG target 3.5.1 tracks treatment coverage for alcohol and drug dependence
Park's Textbook of Preventive and Social Medicine

Summary of Dependence Type by Drug

Drug	Psychic Dependence	Physical Dependence	Tolerance	Withdrawal
Opioids	Strong	Strong	Yes (rapid)	Yes (severe)
Alcohol	Moderate-strong	Yes (develops slowly)	Yes	Yes (severe; seizures)
Cocaine	Strong	Minimal	No	Mild
Amphetamines	Strong	Moderate	Yes	Yes
Barbiturates	Strong	Strong	Yes	Yes (severe)
Cannabis	Moderate	Mild	Mild	Mild
Benzodiazepines	Moderate	Yes	Yes	Yes (severe)
LSD	Minimal	None	None	None
Tobacco	Strong	Yes	Yes	Yes

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