When to use this diagnosis

• Patient presents with signs of intoxication or withdrawal but is unable/unwilling to provide substance history.
• No immediate access to toxicology or when results are pending and clinical decisions are urgent.
• Polysubstance use suspected and specific agent identification is not feasible at presentation.
• Presentation is atypical or drug market includes novel psychoactive substances not covered by routine screens.

Clinical presentations

• Intoxication: altered consciousness, agitation, stupor, respiratory depression (opioids), sympathomimetic signs (tachycardia, hypertension), hallucinations.
• Withdrawal: tremor, autonomic hyperactivity, nausea/vomiting, seizures (alcohol or benzodiazepine withdrawal), delirium tremens.
• Substance-induced psychiatric symptoms: psychosis, mood disturbance, severe anxiety, self-harm risk.
• Medical complications: rhabdomyolysis, aspiration pneumonia, arrhythmias, acute kidney injury, overdose.

Assessment — immediate priorities

1. ABC and resuscitation: airway protection, oxygen, ventilation, circulatory support. Naloxone for suspected opioid overdose if indicated.
2. Vital signs & observations: continuous monitoring for respiratory compromise, ECG for arrhythmias, temperature for hyperthermia.
3. Focused history: collateral from companions, prior records, prescription bottles, empty packages; observe for injection marks.
4. Toxicology screen: urine and blood where available, but interpret clinically — many substances and novel agents may be undetected.
5. Medication review: note prescribed benzodiazepines, opioid agonists, or other agents affecting management.
6. Mental state and risk assessment: suicidality, aggression, capacity for consent, withdrawal risk.

Investigations — essential and targeted

• Point-of-care: blood glucose, pulse oximetry, ECG, capillary ketones (if diabetic risk).
• Blood tests: CBC, electrolytes, renal & liver function, creatine kinase, coagulation profile, arterial blood gas if respiratory compromise suspected.
• Urine toxicology and serum drug levels where useful (e.g., acetaminophen, salicylates, lithium, carbamazepine, ethanol).
• Other tests guided by presentation: chest x-ray (aspiration), CT head (trauma, focal neurology), pregnancy test in women of childbearing age.

Acute management — symptom & harm reduction focused

• General measures: resuscitate, maintain hydration, correct hypoxia, treat hyper/hypotension, control temperature.
• Specific antidotes: naloxone for opioids, flumazenil generally avoided unless specific indication and monitored setting due to seizure risk in chronic benzodiazepine users.
• Manage agitation safely: non-pharmacological de-escalation first; if drug therapy required, use short-acting agents at lowest effective dose (e.g., haloperidol, olanzapine) with ECG monitoring when indicated.
• Treat withdrawal: benzodiazepine protocols for alcohol withdrawal (thiamine replacement), benzodiazepine tapering strategies, consider phenobarbital in severe cases; clonidine or symptomatic care for opioid withdrawal unless initiating opioid agonist therapy.
• Overdose complications: manage seizures, rhabdomyolysis (IV fluids), aspiration/airway protection, arrange critical care for severe cases.

Short-term disposition & safety planning

• Admit to appropriate setting: medical ward, observation unit or ICU depending on severity.
• Consider supervised observation for patients with ongoing intoxication risk or incomplete reversal.
• Ensure safe storage and disposal of medications and substances; remove access to driving and machinery until medically cleared.
• Document decision-making capacity and plan for substitute decision-makers if capacity impaired.

Longer-term care & referral

• Link to addiction services for assessment and treatment (psychosocial interventions, opioid agonist therapy where indicated, benzodiazepine management).
• Harm reduction: provide naloxone training and kit for opioid users, safer-use advice, needle/syringe program referrals.
• Mental health support for substance-induced psychiatric symptoms; consider dual-diagnosis services.
• Social work involvement: housing, legal issues, family support and vocational rehabilitation.

Key takeaways

• Prioritise airway, breathing and circulation — naloxone for suspected opioid overdose can be life-saving.
• Use clinical judgment; toxicology screens are supportive but not definitive for many novel agents.
• Manage withdrawal, treat complications and arrange appropriate disposition (observation, ward or ICU).
• Provide harm reduction, linkage to addiction services and document capacity and medico-legal decisions clearly.