About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- Treat intoxication first as a medical presentation: ABCs, glucose, temperature, oxygenation, trauma, toxidrome, co-ingestions, and withdrawal risk
- Opioid toxicity is respiratory depression with miosis and coma — give naloxone and support ventilation
- Stimulant intoxication causes sympathetic excess: agitation, tachycardia, hypertension, hyperthermia, chest pain, psychosis, seizures; benzodiazepines are first-line sedation
- Alcohol intoxication can mask head injury, hypoglycaemia, Wernicke encephalopathy, suicidal intent, and withdrawal risk
- Canadian practice emphasises harm reduction: naloxone kits, safer-use counselling, opioid agonist therapy, trauma-informed care, and linkage rather than shame
Approach to the Presentation
Substance use and intoxication should be approached with two parallel questions: what immediate toxidrome or complication could kill the patient, and what longer-term intervention reduces future harm? Initial care is airway, breathing, circulation, glucose, temperature, trauma, oxygenation, ECG when indicated, and co-ingestion history. Once stable, assess substance, route, dose, timing, tolerance, pattern of use, previous overdoses, withdrawal history, mental health, pregnancy, infectious risk, housing, violence, and readiness for change. Use non-stigmatising language and offer harm reduction and evidence-based addiction treatment.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Opioid overdose | must-not-miss | Respiratory depression, reduced consciousness, miosis, cyanosis, snoring respirations; fentanyl contamination common | Clinical diagnosis; response to naloxone; consider glucose and co-ingestions |
| Alcohol intoxication with occult trauma or hypoglycaemia | must-not-miss | Ataxia, slurred speech, disinhibition, vomiting, low GCS; may conceal head injury, sepsis, hypoglycaemia, overdose, or suicide attempt | Glucose, vitals, trauma exam, CT head if indicated, ethanol/co-ingestion testing when useful |
| Stimulant intoxication / sympathomimetic toxidrome | must-not-miss | Cocaine/amphetamine: agitation, mydriasis, diaphoresis, tachycardia, hypertension, hyperthermia, chest pain, seizures, psychosis | Clinical toxidrome; ECG/troponin if chest pain; CK/renal function if hyperthermia/rhabdomyolysis |
| Sedative-hypnotic intoxication | must-not-miss | Benzodiazepines, Z-drugs, barbiturates, alcohol combinations: respiratory depression, ataxia, slurred speech, coma | Clinical; co-ingestion work-up; avoid flumazenil except specific iatrogenic cases |
| Cannabis intoxication / cannabis-induced anxiety or psychosis | common | Anxiety, panic, tachycardia, impaired coordination, derealisation, paranoia, hallucinations; edibles delayed/prolonged | History and urine toxicology when helpful; monitor until clinically sober |
| Substance-induced psychosis | common | Paranoia, hallucinations, agitation after cannabis/stimulants/hallucinogens/steroids; may persist beyond acute intoxication | Temporal relationship, collateral, tox screen, reassessment after abstinence |
| Underlying psychiatric crisis with substance use | common | Intoxication plus suicidality, trauma, domestic violence, psychosis, mania, or personality disorder crisis | Reassess risk when clinically sober; collateral and records |
| Serotonin syndrome | less common | Agitation, hyperthermia, diaphoresis, diarrhoea, clonus, hyperreflexia after serotonergic drugs/MDMA/MAOI interactions | Hunter criteria; medication/substance history |
| Anticholinergic toxicity | less common | Delirium, dry skin, mydriasis, urinary retention, tachycardia, hyperthermia | Clinical toxidrome; ECG for QRS widening if TCA possible |
Red Flags & Key History
Symptoms
Respiratory depression, cyanosis, low GCS, recurrent sedation after naloxone
Hyperthermia, rigidity, clonus, seizures, severe agitation, chest pain, or severe hypertension
Head injury, anticoagulant use, fall, assault, or unexplained reduced consciousness
Co-ingestion: alcohol + opioids/benzodiazepines, acetaminophen, TCAs, or unknown tablets
Suicidal intent, self-harm, violence risk, or inability to keep self safe when intoxicated
Prior overdose, escalating tolerance, using alone, injecting, fentanyl exposure
Signs
Pinpoint pupils + bradypnoea + coma (opioids)
Mydriasis + diaphoresis + agitation + hyperthermia (stimulants)
Ataxia, nystagmus, slurred speech, vomiting, aspiration risk (alcohol/sedatives)
Track marks, skin infections, endocarditis signs, abscesses
Dehydration, rhabdomyolysis signs, severe muscle tenderness
Approach to Investigation
First-line
ABCs, vitals, oxygen saturation, temperature, glucoseImmediate screen for reversible life threats: hypoxia, hypoglycaemia, hyperthermia, shock, airway obstruction, aspiration
Toxidrome-based examinationPupils, sweating/dryness, bowel sounds, tone/reflexes/clonus, mental status, skin, trauma, injection sites
ECGIndicated for stimulant intoxication, chest pain, syncope, electrolyte disturbance, antipsychotic/TCA/unknown overdose, or severe agitation
Targeted labsElectrolytes, creatinine, CK, LFTs, acetaminophen/salicylate levels, pregnancy test, ethanol level, troponin, VBG/ABG depending on presentation
Second-line
Urine drug screenMay support but does not replace clinical assessment; false positives/negatives occur
CT head / trauma imagingFor reduced GCS not explained by intoxication, head trauma, anticoagulation, focal signs, persistent vomiting, or failure to improve
Infectious screeningHIV, hepatitis B/C, STI testing, pregnancy, TB risk, blood cultures/echo if endocarditis suspected
Specialist
Poison centre consultationFor severe, unknown, mixed, paediatric, pregnancy, uncommon, or long-acting intoxications
Addiction medicine / RAAMFor opioid agonist treatment, alcohol use disorder treatment, harm reduction, and follow-up linkage
Management Principles
CAMH Opioid Use Guidance + CCSA Alcohol/Cannabis Resources + CFPC Addiction Medicine resources1
Immediate stabilisation
- ABCs, oxygen, ventilation support, IV access, glucose, temperature control, trauma precautions, and continuous monitoring when severe
- Opioid toxicity: naloxone titrated to adequate ventilation, not full withdrawal; observe for re-sedation
- Alcohol/sedative intoxication: airway protection, thiamine before glucose if Wernicke risk and glucose can be safely delayed; treat hypoglycaemia urgently regardless
2
Toxidrome-specific treatment
- Stimulants: benzodiazepines, cooling, IV fluids, treat seizures; evaluate chest pain for ACS/aortic dissection
- Cannabis: reassurance, low-stimulus environment, benzodiazepine if severe panic/agitation, antipsychotic if severe psychosis persists
- Serotonin syndrome: stop serotonergic agents, benzodiazepines, cooling, cyproheptadine for moderate-severe cases
3
Harm reduction and long-term care
- Provide take-home naloxone, safer-use counselling, do-not-use-alone advice, supervised consumption information where available
- Offer opioid agonist therapy linkage: buprenorphine/naloxone or methadone through appropriate local pathways
- For alcohol use disorder: discuss pharmacotherapy, counselling, withdrawal planning, and CCSA lower-risk guidance
Complications & Pitfalls
- Anchoring on intoxication: Intoxicated patients can also have sepsis, head injury, hypoglycaemia, overdose, or stroke.
- Too much naloxone: Abrupt full reversal can precipitate severe withdrawal and agitation; titrate to breathing.
- Missing acetaminophen: Always consider acetaminophen level in intentional or unknown overdose.
- Discharge before sober reassessment: Suicidal intent and capacity must be reassessed when clinically sober.
MCCQE1 Exam Tips
- 1Opioid overdose triad: coma, miosis, respiratory depression; lifesaving action is ventilation + naloxone
- 2Stimulant intoxication with agitation/hypertension: benzodiazepines are first-line; look for hyperthermia and rhabdomyolysis
- 3Alcohol intoxication plus low GCS: check glucose and trauma; do not assume drunk means safe
- 4Cannabis edibles have delayed onset and prolonged duration — a common Canadian counselling point
- 5Urine drug screens do not rule out intoxication; management is based on clinical toxidrome
- 6Treat substance use disorder as a chronic medical condition; offer harm reduction and evidence-based treatment
practicetest your knowledge on substance use & intoxication (alcohol, opioids, stimulants, cannabis)Apply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — psychiatric and beyond.
open q-bank