Substance Use Disorder — Alcohol

• GABAergic and Glutamatergic Dysregulation (Primary Mechanism): Alcohol's initial reinforcing effects result from potentiation of gamma-aminobutyric acid (GABA) type A receptors, the brain's primary inhibitory neurotransmitter system, producing sedation, anxiolysis, and reward. Simultaneously, alcohol inhibits N-methyl-D-aspartate (NMDA) glutamatergic receptors, the primary excitatory neurotransmitter system. With chronic exposure, the brain adapts through allostatic changes: GABA-A receptor downregulation and desensitization occur, while compensatory upregulation and increased function of glutamatergic NMDA receptors develops. This neuroadaptation produces tolerance (requiring more alcohol for the same effect) and physical dependence (withdrawal symptoms when alcohol is removed). Upon cessation, the unopposed glutamatergic hyperactivity drives the acute withdrawal syndrome characterized by tremor, autonomic hyperactivity, hallucinations, and potentially life-threatening seizures and delirium tremens.

• Dopaminergic Reward System Sensitization: Alcohol, like all drugs of abuse, activates the mesolimbic dopamine pathway, particularly the ventral tegmental area (VTA) to nucleus accumbens circuit, producing the rewarding "high" that reinforces continued use. Chronic alcohol use produces sensitization of this reward pathway while simultaneously producing anhedonia (inability to experience pleasure from non-drug stimuli) through dysregulation of dopamine D2 receptors in the nucleus accumbens and prefrontal cortex. This creates a powerful incentive-sensitization state where environmental cues become strongly associated with alcohol use and trigger intense cravings. Additionally, stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis and corticotropin-releasing factor (CRF) systems contributes to negative reinforcement—individuals drink to alleviate negative emotional states and withdrawal symptoms.

• Prefrontal Cortex Dysfunction and Impaired Decision-Making: The dorsolateral prefrontal cortex (dlPFC) and orbitofrontal cortex (OFC), critical for impulse control, judgment, and evaluation of consequences, show both structural atrophy and functional hypoactivity in individuals with chronic AUD. This is accompanied by hyperactivity in the amygdala and anterior insula, which process emotional salience and stress. The resulting neural imbalance produces impaired inhibitory control (inability to resist alcohol use despite knowing consequences), poor judgment regarding drinking behavior, and difficulty with decision-making. Neuroimaging demonstrates reduced gray matter volume in the prefrontal cortex and anterior cingulate cortex proportional to drinking history, and functional connectivity abnormalities that normalize only with months to years of abstinence.

• Neuroinflammation and Stress Response System: Chronic alcohol exposure activates microglial cells in the brain through toll-like receptor 4 (TLR4) signaling, producing a pro-inflammatory state characterized by elevated cytokines (IL-1β, TNF-α, IL-6). This neuroinflammation contributes to cognitive impairment, depression, anxiety, and perpetuation of addiction-like behaviors. Additionally, chronic alcohol dysregulates the HPA axis, producing blunted cortisol responses to stress in some individuals and excessive responses in others, contributing to anxiety and negative reinforcement of drinking.

• Genetic and Epigenetic Factors: Genome-wide association studies (GWAS) have identified multiple loci associated with AUD risk, including genes encoding alcohol dehydrogenase (ADH1B, ADH1C), aldehyde dehydrogenase (ALDH2), and GABA and glutamate receptors. The ALDH2 variant (particularly common in East Asian populations) produces aldehyde accumulation with alcohol consumption, causing the "flushing reaction" (facial flushing, nausea, headache) and is protective against AUD development. Epigenetic modifications (DNA methylation and histone acetylation) of genes involved in addiction circuitry become established with chronic alcohol use, potentially perpetuating the addicted state. Polymorphisms in serotonin transporter genes, dopamine D2 receptor genes, and genes regulating GABA and glutamate also influence AUD susceptibility.

• Organ-System Pathophysiology: Beyond the central nervous system, alcohol produces direct toxic effects on hepatocytes through acetaldehyde accumulation and oxidative stress, leading to fatty liver disease, hepatitis, and cirrhosis. In the heart, chronic alcohol produces dilated cardiomyopathy through direct myocyte injury, oxidative damage, and mitochondrial dysfunction. In the pancreas, alcohol triggers acinar cell injury through direct toxicity and oxidative stress, producing acute and chronic pancreatitis. Alcohol also damages the gastrointestinal epithelium, increasing intestinal permeability and bacterial lipopolysaccharide (LPS) translocation, which exacerbates hepatic inflammation and cirrhosis.

• Genetic Predisposition (50-60% heritability): First-degree relatives of individuals with AUD have 3-4 times higher lifetime risk of developing AUD. The "alcoholic liver disease" phenotype and early-onset AUD show stronger genetic influences. Protective variants include ALDH2 and ADH1B variants (particularly in East Asian populations) that produce aversive reactions to alcohol, making alcohol use inherently punishing. Male sex is the strongest demographic predictor of AUD, with males showing earlier onset and more severe courses.

• Environmental and Social Factors: Early age of first drinking (before age 15) is associated with 5-fold increased risk of developing AUD, likely reflecting greater neuroplasticity in the developing adolescent brain to undergo addiction-related changes. Peer influence, family modeling of heavy drinking, and social environments normalizing alcohol use substantially increase risk. Trauma exposure (childhood abuse, combat, intimate partner violence) is one of the strongest social risk factors, with approximately 50% of individuals with PTSD also meeting criteria for AUD, reflecting self-medication of PTSD symptoms.

• Psychiatric Comorbidity (Critical Risk Factor): Approximately 75% of individuals with AUD meet criteria for another psychiatric disorder. Depression (lifetime prevalence ~35%) and anxiety disorders (~35%) frequently precede AUD onset, with individuals using alcohol to self-medicate dysphoria and anxiety. Post-traumatic stress disorder (PTSD) shows particularly high comorbidity (25-40%), with alcohol dampening intrusive memories and hyperarousal. Attention-deficit/hyperactivity disorder (ADHD) in adolescents is an established risk factor for early-onset AUD. Bipolar disorder and schizophrenia also show elevated AUD prevalence. The relationship between psychiatric disorder and AUD is often bidirectional, with alcohol use exacerbating psychiatric symptoms through disruption of neurotransmitter systems.

• Personality and Psychological Factors: High novelty-seeking, impulsivity, and low harm-avoidance (temperamental traits) predict AUD development. Poor coping skills, low self-efficacy, and difficulty managing negative emotions increase vulnerability. Individuals with antisocial personality disorder show particularly early and severe AUD.

• Medical Comorbidities: Chronic pain conditions frequently lead to alcohol use as self-medication, creating a pathway to AUD. Sleep disorders (insomnia, sleep apnea) are both risk factors and consequences of AUD. Liver disease can predispose to AUD through altered alcohol metabolism (see Complications).

• Loss of Control and Continued Use Despite Harm (Core Behavioral Features): Individuals with AUD demonstrate inability to limit drinking once started (often drinking more or longer than intended), continued heavy drinking despite knowledge of physical, psychological, or social harm, and persistence of drinking despite recurrent interpersonal or occupational problems caused by alcohol. The desire to cut down or control drinking is frequently present but unsuccessful. This loss of behavioral control reflects the neurobiological changes in prefrontal circuits described above and is the pathognomonic feature distinguishing AUD from hazardous or harmful drinking patterns.

• Tolerance and Physical Dependence: Tolerance manifests as needing progressively larger amounts of alcohol to achieve intoxication or the desired effect, or markedly diminished effect from the same amount. Individuals may note they can "hold their liquor" better than non-dependent drinkers. Physical dependence is evidenced by withdrawal symptoms (tremor, sweating, anxiety, insomnia) when alcohol use is reduced or stopped, or drinking to relieve or avoid withdrawal symptoms. This reflects the neuroadaptation of GABAergic and glutamatergic systems and is a highly specific indicator of physiological dependence.

• Craving and Compulsive Seeking: Intense craving for alcohol (subjectively rated desire to use) occurs spontaneously and particularly in response to alcohol-associated cues (bars, specific people, stress, negative mood). Individuals with AUD demonstrate compulsive behavioral patterns of seeking alcohol despite attempts to abstain, often multiple failed attempts to cut down or quit. This reflects sensitization of the dopamine reward system and associative learning processes.

• Negative Mood and Withdrawal-Driven Drinking: Dysphoria, depression, and anxiety are cardinal features, appearing both as consequences of chronic alcohol use (through effects on serotonergic and noradrenergic systems) and as motivations for continued drinking (negative reinforcement). Individuals report drinking to cope with stress, anxiety, or depressed mood. As addiction progresses, the desire to relieve negative mood and withdrawal symptoms becomes a primary motivation, superseding pleasure-seeking.

• Cognitive and Behavioral Changes: Impaired judgment is evident as continued drinking despite awareness of consequences, financial problems, or legal issues. Reduced engagement in non-drinking activities and social withdrawal from non-drinking relationships occurs as drinking becomes the central organizing activity. Memory blackouts during drinking episodes (particularly with binge drinking) reflect hippocampal dysfunction and are concerning for rapid progression.

• Physical Examination Findings Reflecting Chronic Alcohol Use:
• Hepatic stigmata: Spider angiomas, palmar erythema, jaundice, hepatomegaly (often with cirrhotic change producing contraction), ascites, splenomegaly (from portal hypertension)
• Neurological findings: Tremor (coarse action tremor, best seen with arms extended), hyperreflexia, horizontal nystagmus, ataxia/gait disturbance, peripheral neuropathy (distal symmetric, sensorimotor, reflecting thiamine and pyridoxine deficiency)
• Vascular stigmata: Telangiectasia, varices (particularly esophageal, identified on endoscopy)
• Skin findings: Poor hygiene, bruising from falls, abscesses from injected contaminants (if combining with intravenous drugs)
• Cardiovascular: Hypertension, irregular rhythm (atrial fibrillation from alcohol-induced cardiomyopathy), signs of congestive heart failure
• Endocrine: Gynecomastia, testicular atrophy, sexual dysfunction (from altered gonadal hormone metabolism)

• Alcohol Withdrawal Syndrome (Important Clinical Variant): When individuals with physiological dependence cease or significantly reduce drinking, a stereotyped sequence of withdrawal symptoms develops. Early withdrawal (6-12 hours post-cessation) includes tremor (particularly of the hands), diaphoresis, tachycardia, hypertension, anxiety, insomnia, gastrointestinal upset, and headache, reflecting unopposed sympathetic activation. Hallucinosis (visual, auditory, or tactile hallucinations, usually frightening) can occur at 12-24 hours with relatively preserved orientation and insight ("alcoholic hallucinosis"), and can persist 1-2 days. Withdrawal seizures (generalized tonic-clonic) typically occur 6-48 hours after last drink in approximately 5-15% of individuals undergoing withdrawal, and in 60% of those with seizures, a second seizure occurs within 6 hours. Delirium tremens (DTs) represents the most severe form of withdrawal, occurring 48-96 hours after cessation, characterized by confusion/disorientation, autonomic hyperactivity (hyperthermia up to 40°C, severe tachycardia, hypertension, profuse diaphoresis), hallucinations, agitation, and delusional ideation. DTs carries mortality of 10-15% if untreated.

• Drinking Patterns and Temporal Course: Individuals with AUD may show various drinking patterns: "daily heavy drinking" (drinking substantial amounts most or all days), "binge drinking" (consuming 5+ drinks in ~2 hours for men, 4+ for women, on multiple occasions), or cycles of periods of heavy drinking alternating with abstinence. Some individuals present acutely after a binge with intoxication and withdrawal symptoms; others present with chronic daily drinking patterns. Individuals without complete abstinence frequently experience "loss of control" episodes where they intend to drink moderately but are unable to stop until significantly intoxicated.

• DSM-5 Diagnostic Criteria for Alcohol Use Disorder: AUD is diagnosed when an individual exhibits a problematic pattern of alcohol use leading to clinically significant impairment or distress, manifested by at least 2 of 11 criteria occurring within a 12-month period. These criteria include: (1) drinking more or for longer than intended; (2) persistent desire or unsuccessful efforts to cut down or control use; (3) great deal of time spent obtaining, using, or recovering from effects; (4) craving or strong desire to use; (5) recurrent use resulting in failure to fulfill major role obligations; (6) continued use despite recurrent social or interpersonal problems; (7) giving up or reducing important activities; (8) recurrent use in physically hazardous situations; (9) continued use despite physical or psychological harm; (10) tolerance (markedly increased amounts needed); (11) withdrawal symptoms. Severity is graded: mild (2-3 criteria), moderate (4-5 criteria), severe (6+ criteria). This framework should be systematically applied; simply asking "Do you have a drinking problem?" is insufficient as patients often minimize or deny problems.

• Clinical History and Screening Instruments: The AUDIT (Alcohol Use Disorders Identification Test) is a validated 10-item WHO screening tool asking about frequency and quantity of drinking, control issues, and consequences; scores ≥8 (or ≥7 for women) suggest hazardous drinking or AUD with good sensitivity (90-95%) and specificity (80-90%). The AUDIT-C (abbreviated version using first 3 AUDIT items on quantity, frequency, and binge frequency) is quick (takes <2 minutes) and has sensitivity of 86-89% for AUD. The CAGE questionnaire (Cut down, Annoyed, Guilty, Eye-opener) is even briefer (4 items) with sensitivity ~75% for AUD but can miss early-stage disease. The Alcohol Use Disorder Test (ASSIST) is another validated brief tool. Key history elements include: age of first drink, age when drinking became problematic, typical quantity and frequency of current drinking, longest period of abstinence, previous treatment attempts, family history of AUD, withdrawal symptoms experienced, medical and psychiatric complications, and psychosocial consequences.

• Laboratory Tests (Biomarkers):
• Liver function tests (LFTs): Elevated aspartate aminotransferase (AST

Immediate stabilisation (withdrawal management)

• Risk stratification: score severity with the CIWA-Ar; the ASAM 2020 Alcohol Withdrawal Management guideline endorses symptom-triggered dosing over fixed-schedule dosing in monitored settings because it reduces total benzodiazepine exposure and length of stay. Patients with prior delirium tremens or withdrawal seizures, unstable vitals, or significant comorbidity warrant inpatient/ICU care.
• Thiamine before glucose: parenteral thiamine precedes any dextrose-containing fluid, since a carbohydrate load in a thiamine-depleted patient can precipitate Wernicke encephalopathy. Replete magnesium, potassium, and phosphate.
• Benzodiazepines (first-line): e.g., chlordiazepoxide or diazepam (long-acting, self-tapering) restore GABA-A tone against unopposed NMDA hyperexcitability. In cirrhosis or advanced age use lorazepam or oxazepam, which undergo glucuronidation only and lack active metabolites.
• Escalation: benzodiazepine-refractory withdrawal or delirium tremens calls for phenobarbital (acts at GABA-A independent of an endogenous ligand) or continuous-infusion sedation with airway control. Adjunctive antipsychotics (haloperidol) may control agitation/hallucinations but never as monotherapy — they lower the seizure threshold and do not treat the underlying GABA deficit. Alpha-2 agonists (dexmedetomidine, clonidine) and beta blockers blunt autonomic signs but mask CIWA scoring and are adjuncts only.

Relapse-prevention pharmacotherapy (after withdrawal)

• Naltrexone (opioid antagonist): first-line per the APA 2018 Practice Guideline; blunts endogenous-opioid-mediated dopamine reward, reducing heavy drinking days. Oral daily or extended-release monthly injection. Abstinence is not required to start.
• Acamprosate (NMDA/glutamate modulator): co–first-line, preferred when hepatic disease precludes naltrexone; requires dose adjustment and is contraindicated in severe renal impairment.
• Second-line/off-label: topiramate or gabapentin, suggested by the APA when first-line agents fail or are contraindicated. Disulfiram (aldehyde dehydrogenase inhibitor) is second-line, reserved for motivated, supervised, abstinent patients.
• Psychosocial care: CBT, motivational enhancement, contingency management, and mutual-help groups (AA) are integral, not optional.

Definitive and contraindicated

• Liver transplantation is definitive for end-stage alcohol-associated cirrhosis, with AASLD-supported early transplant in selected patients with severe alcohol-associated hepatitis; corticosteroids (prednisolone) are used for severe alcohol-associated hepatitis by Maddrey discriminant function.
• Contraindicated: naltrexone with current opioid use or opioid agonist therapy (precipitates withdrawal) and in acute hepatitis/liver failure; disulfiram with recent alcohol intake, severe coronary disease, or psychosis; long-term outpatient benzodiazepines in AUD.

Neurologic (several are emergencies)

• Delirium tremens — EMERGENCY: 48–96 h after the last drink; glutamatergic storm producing clouded sensorium plus hyperthermia, severe tachycardia, and diaphoresis. Distinguish from alcoholic hallucinosis, in which sensorium is clear.
• Withdrawal seizures — EMERGENCY: generalized tonic-clonic, typically 6–48 h; recurrence is common. Benzodiazepines, not phenytoin, are the treatment.
• Wernicke encephalopathy — EMERGENCY: thiamine-dependent transketolase failure in mammillary bodies/periaqueductal gray; triad of confusion, ophthalmoplegia/nystagmus, and ataxia (frequently incomplete). Untreated it progresses to Korsakoff syndrome (anterograde amnesia with confabulation), which is largely irreversible.
• Cerebellar degeneration: atrophy of the anterior/superior vermis → wide-based gait ataxia with relatively spared arms.
• Osmotic demyelination: overly rapid correction of chronic hyponatremia → locked-in quadriparesis days later.
• Peripheral neuropathy: distal symmetric stocking-glove sensory loss from thiamine/B-vitamin deficiency and direct axonal toxicity.

Hepatic and GI

• Steatosis → alcoholic hepatitis → cirrhosis: acetaldehyde and NADH excess; AST:ALT ratio >2:1 with both typically only modestly elevated. Cirrhosis brings variceal hemorrhage, ascites/spontaneous bacterial peritonitis, hepatic encephalopathy, and hepatocellular carcinoma.
• Pancreatitis: acinar injury; epigastric pain radiating to the back with elevated lipase. Necrotizing disease is an emergency.
• Mallory-Weiss tear (retching → mucosal tear, hematemesis) versus Boerhaave perforation — EMERGENCY with subcutaneous emphysema and mediastinitis.

Cardiac, metabolic, hematologic, oncologic

• Dilated cardiomyopathy and holiday heart (new atrial fibrillation after a binge).
• Alcoholic ketoacidosis: anion-gap acidosis with low/normal glucose and prominent beta-hydroxybutyrate; treat with saline, thiamine, then dextrose.
• Macrocytosis, thrombocytopenia, folate deficiency; hypoglycemia from impaired gluconeogenesis.
• Malignancy: acetaldehyde is a carcinogen — oropharyngeal, esophageal squamous cell, liver, breast, and colorectal cancer.
• Fetal alcohol spectrum disorder: smooth philtrum, thin vermilion border, short palpebral fissures, growth restriction.

Treatment-related

• Benzodiazepine over-sedation/respiratory depression, worsened by cirrhosis with long-acting agents; high-dose IV lorazepam infusions can cause propylene glycol toxicity (anion-gap acidosis, hyperosmolar gap, renal injury).
• Disulfiram–ethanol reaction: acetaldehyde accumulation → flushing, vomiting, hypotension; can be life-threatening.
• Naltrexone: precipitated opioid withdrawal in opioid-exposed patients; dose-related transaminase elevation. Acamprosate: diarrhea and accumulation in renal impairment.

• Thiamine before glucose, always: in a malnourished drinker, a dextrose bolus consumes residual thiamine and can precipitate Wernicke encephalopathy. The single best next step in a confused, ataxic, ophthalmoplegic drinker is IV thiamine, then glucose.
• Timing is the discriminator: tremor/autonomic signs 6–12 h → alcoholic hallucinosis with clear sensorium 12–24 h → withdrawal seizures 6–48 h → delirium tremens with clouded sensorium 48–96 h. Confusion is what separates DTs from hallucinosis — the most commonly tested distinction.
• "LOT" benzodiazepines in liver disease: Lorazepam, Oxazepam, Temazepam bypass CYP oxidation and are glucuronidated only, so they do not accumulate in cirrhosis. Chlordiazepoxide/diazepam are fine in intact livers and self-taper.
• Symptom-triggered dosing guided by CIWA-Ar (ASAM 2020) is preferred to fixed schedules in monitored patients — expect a stem where escalating CIWA scores demand more benzodiazepine, not an antipsychotic.
• Naltrexone is first-line for AUD (APA 2018) and does not require the patient to be abstinent — but screen for opioid use first, because it precipitates withdrawal and blocks analgesia. Choose acamprosate when hepatic disease is the issue and avoid acamprosate in renal failure.
• The classic distractor is disulfiram: examiners offer it for the newly detoxified or ambivalent patient. It is second-line, requires abstinence and supervision, and is not the answer for someone still drinking.
• AST:ALT >2:1 with modest transaminase elevation is the buzzword for alcohol-associated liver disease; macrocytosis without anemia and elevated GGT are supporting clues.
• Antipsychotics are never monotherapy for withdrawal delirium — they lower the seizure threshold and do not correct the GABA deficit. Escalate instead to phenobarbital or continuous sedation with airway protection.
• Screen everyone: the USPSTF recommends screening adults, including pregnant persons, for unhealthy alcohol use with brief counseling — AUDIT-C in a routine-visit stem is the correct first step.