Cannabis Poisoning

Overview and Toxicology

• CB1 receptors - found mostly in the CNS (responsible for psychoactive effects)
• CB2 receptors - found primarily on peripheral immune cells

• Dried flowering tops (marijuana/ganja)
• Resin (hashish/charas)
• Liquid preparations (bhang)

Pharmacokinetics

Signs and Symptoms of Acute Poisoning

Stage 1 - Inebriation (lower doses)

• Euphoria, relaxation, laughter
• Altered time and space perception
• Short-term memory impairment
• Synesthesias ("seeing sounds, smelling colors")
• Conjunctival injection (the only truly reliable physiologic sign)
• Mild tachycardia
• Decreased intraocular pressure
• Increased appetite ("munchies")
• Psychomotor impairment (driving, complex tasks)

Stage 2 - Narcosis (higher doses: 0.5-1 mg/kg oral)

• Giddiness, ataxia
• Confused, rambling speech
• Tingling and numbness of skin
• Drowsiness progressing to deep sleep
• Lassitude and impaired mental function on waking
• Hallucinations at 300-480 mcg/kg oral
• Delirium, homicidal ideation, or fear of death in extremes

Severe / Massive Ingestion (especially edibles)

• Profound ataxia, vomiting, agitation, anxiety
• CNS depression

Pediatric Exposures (particularly dangerous)

• Hypothermia
• Ataxia, nystagmus, tremor
• Labile affect, tachycardia
• Rapid-onset drowsiness, hypotonia, lethargy
• Rarely: seizures
• Large ingestions can cause coma, airway obstruction, and respiratory failure requiring intubation

Fatal Dose and Period

• Fatal dose: 1,000-2,000 mg (or ~30 mg/kg)
  • Charas: ~2 g | Ganja: ~8 g | Bhang: ~10 g/kg
• Fatal period: Rarely fatal; period varies from 12 hours to several days
• The acute toxicity of natural cannabis is very low - there are no documented cases of fatal cannabis poisoning in humans from natural cannabis alone
• Animal data suggests the LD50 in humans could not be achieved by smoking or swallowing cannabis

⚠️ Synthetic cannabinoids are far more dangerous - see below

Cardiovascular Effects

• Mild tachycardia and transient BP changes in healthy young users (clinically minimal)
• In older adults with hypertension, coronary disease, or cerebrovascular disease: can provoke myocardial infarction
• Case reports of serious cardiovascular events in heavy daily smokers
• Increased cardiac-related deaths in hospital data following medical cannabis policy passage

Synthetic Cannabinoids - Distinct and Dangerous

• Profound agitation and aggression → CNS depression
• Seizures
• Tachycardia → bradycardia; hypertension → hypotension
• Ischemic stroke, cardiac toxicity

Differential Diagnosis

Laboratory Testing

• Urine immunoassay is the standard screening test; turns positive within 1 hour of smoking
• A positive urine screen does not indicate acute intoxication - THC metabolites persist for weeks
• Blood THC >10-15 ng/mL suggests recent use; THC:9-carboxy-THC ratio (1:1) suggests use within past 20-40 minutes
• Colorado/Washington standard: Blood THC >5 ng/mL is evidence of impaired driving (requires behavioral confirmation)
• Saliva testing is available; less sensitive
• Synthetic cannabinoids are NOT detected by routine urine toxicology screens
• Order a full metabolic panel, coagulation studies (PT/INR) if synthetic cannabinoid use is suspected (brodifacoum contamination)

Management

1. Mainly supportive care - most patients recover without specific intervention
2. Oral ingestion: gastric lavage + purgatives (if within appropriate window)
3. Oxygen and airway support as needed; artificial respiration for respiratory failure
4. Calm reassurance for anxiety/panic; quiet environment ("talk-down")
5. Benzodiazepines (e.g., lorazepam) for severe agitation, anxiety, or seizures
6. Pediatric cases with coma: airway management may require intubation
7. Symptomatic treatment throughout

• Supportive care with close monitoring of vitals
• Benzodiazepines for agitation and seizures
• Cardiac monitoring; antiarrhythmics if needed
• If brodifacoum contamination suspected: Vitamin K1 (high-dose, long-term oral supplementation)
• Fresh frozen plasma for acute life-threatening bleeding

Autopsy Findings (Fatal Cases - Extremely Rare)

• Congested lungs and brain
• Petechial hemorrhages in some cases
• Generally non-specific; diagnosis relies on toxicological analysis

Chronic Poisoning Effects

• Amotivational syndrome (controversial)
• Increased risk of bronchitis, COPD, respiratory cancers (with smoking)
• Cognitive impairment with heavy use
• Cannabis use disorder / dependence
• Increased risk of psychosis with heavy/early use - especially with high-THC, low-CBD strains
• Possibly increased risk of testicular cancer (nonseminoma type)
• Fetal effects: lower birth weight, transient behavioral effects if used during pregnancy
• Reproductive effects: reduced testosterone, sperm motility; disrupted ovulatory cycles

• [Rosen's Emergency Medicine](Rosen's Emergency Medicine, 9780323757898) - Cannabis and Synthetic Cannabinoids chapter
• [Kaplan & Sadock's Comprehensive Textbook of Psychiatry](Kaplan & Sadock's, 9781975175733) - Adverse Effects of Cannabis Use
• [PC Dikshit Textbook of Forensic Medicine and Toxicology](PC Dikshit Forensic Medicine, 9788188867967) - Cannabis Poisoning