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|Drug Toxicity - clinical assessment
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|Drug Toxicity with Specific Antidotes
🌿 About
- Cannabis toxicity results from the acute or chronic use of derivatives of the Cannabis sativa plant. The main psychoactive compound is Δ⁹-tetrahydrocannabinol (THC), which acts on CB₁ receptors in the brain and CB₂ receptors in immune tissues.
- Common preparations include:
- Marijuana: dried flowers and leaves.
- Hashish: resin extract.
- Oils / “Wax” / Edibles: concentrated THC derivatives of variable potency.
- Routes: Smoking → effects within 10–20 min; oral ingestion → delayed onset (1–2 h) but prolonged duration (up to 12 h). Edibles are a common cause of accidental overdose.
💡 Teaching point: THC acts as a partial agonist at central CB₁ receptors, reducing GABA and glutamate release → altered perception, coordination, and mood. Chronic exposure down-regulates CB₁ receptors, explaining tolerance and withdrawal.
🧠 Clinical Features
- Mild / Low dose: Euphoria, altered time perception, laughter, mild ataxia, increased appetite (“munchies”), tachycardia, dry mouth, mild hypertension.
- Moderate / High dose: Panic attacks, severe anxiety, hallucinations, paranoid delusions, depersonalisation, transient psychosis, vomiting.
- Severe / Intravenous or Synthetic Cannabinoids: Cardiovascular collapse, renal failure, pulmonary oedema, DIC, seizures, and hyperthermia. “Spice” and other synthetic products have unpredictable potency.
- Withdrawal syndrome (chronic users): Irritability, insomnia, decreased appetite, low mood, tremor, and anxiety beginning 24–72 h after cessation, lasting up to 2 weeks.
🔬 Investigations
- Urine toxicology: detects THC-COOH for 3–7 days (occasional) or up to 30 days (chronic users).
- Blood tests: U&E, LFTs, glucose, creatine kinase (if agitation or hyperthermia), and screen for co-ingestion (e.g., stimulants, alcohol).
- ECG: check for tachyarrhythmia, QT prolongation (particularly if combined with stimulants).
- CT / MRI: only if neurological deficit or suspicion of alternative pathology (e.g., intracranial haemorrhage, encephalitis).
💊 Management
⚠️ Principle: Supportive care is the cornerstone. Specific antidotes do not exist. Treat agitation, prevent complications, and exclude other causes of collapse.
| Clinical Problem |
Management Strategy |
Rationale |
| Agitation / Psychosis |
IV Diazepam 5–10 mg slowly (repeat if required) or IV Haloperidol 2–5 mg for psychotic features. |
Restores sedation, reduces catecholamine surge and panic response. |
| Hypotension |
IV crystalloids (0.9% NaCl or Hartmann’s). If unresponsive → noradrenaline infusion. |
Volume repletion and vascular support; THC-induced vasodilatation can be profound. |
| Hyperthermia |
Active cooling: cooling blankets, ice packs, IV fluids. |
Prevents rhabdomyolysis, renal injury, and CNS damage. |
| Nausea / Vomiting |
Ondansetron 4–8 mg IV or IM. |
Counteracts THC-mediated emetogenic effect (opposite to low-dose antiemetic use). |
| Withdrawal or Dependence |
Supportive counselling, CBT, substance-use referral. Inpatient detox rarely required. |
Addresses behavioural and psychological dependence. |
| IV Cannabis or Synthetic Cannabinoid Use |
Admit for observation (risk of multi-organ failure). Monitor renal, cardiac, and coagulation profiles. |
High risk due to contaminants and unpredictable pharmacodynamics. |
🩺 Follow-Up Care
- Advise against driving or machinery use for 24 h after intoxication.
- Offer referral to local drug and alcohol services (e.g. Change Grow Live, NHS Talking Therapies).
- Educate on risks of synthetic cannabinoids and edibles.
- Screen for concurrent mental health disorders - particularly anxiety, depression, and psychosis.
🧩 Differential Diagnoses
- Stimulant toxicity (amphetamine, cocaine).
- Anticholinergic poisoning.
- Hypoglycaemia or alcohol intoxication.
- First presentation of a primary psychotic disorder.
📚 References
Summary: Cannabis toxicity typically follows a benign course but can cause significant neuropsychiatric disturbance or cardiovascular collapse, particularly with high-potency or synthetic products.
Prompt supportive management and psychosocial follow-up are essential to prevent recurrence and address underlying dependence.
