What is the lethal dose of methamphetamine (methamphetamine) for an average adult?

Methamphetamine Overdose Threshold

There is no universally defined "lethal dose" of methamphetamine, as toxicity varies dramatically based on individual tolerance, route of administration, and co-ingested substances, but documented fatalities have occurred with blood concentrations as low as 3.0 mg/L and as high as 30 mg/L, with a case report of survival after inadvertent injection of approximately 2.3 grams. 1, 2

Documented Fatal and Near-Fatal Cases

Fatal Overdose Case

• A 49-year-old male died after orally ingesting approximately 3 grams (one "8-ball") of methamphetamine 1
• Hospital blood concentration 12 hours post-ingestion: 3.0 mg/L 1
• Autopsy femoral blood concentration: 30 mg/L 1
• Cause of death: cardiac dysrhythmia due to excited delirium from methamphetamine toxicity 1

Survival After Massive Overdose

• A 34-year-old male survived after inadvertently injecting approximately 2.3 grams intravenously 2
• Symptoms included disorientation, hallucinations, hyperthermia, photophobia, orthostasis, and extreme ataxia 2
• Full recovery occurred within 7 days without apparent sequelae 2

Critical Clinical Context

The wide variation between these cases (both involving ~2-3 grams, one fatal and one survived) demonstrates that tolerance is the most critical factor determining toxicity. Chronic users develop significant tolerance, while naive users may experience severe toxicity at much lower doses 3, 2.

Factors Affecting Toxicity

• Route of administration: Intravenous and smoking produce more rapid, intense effects than oral ingestion 3
• Individual tolerance: Chronic users tolerate doses that would be lethal to naive users 3, 2
• Co-ingested substances: Polysubstance use significantly increases overdose risk 4
• Underlying cardiovascular disease: Pre-existing cardiac conditions increase mortality risk 3

Clinical Presentation of Overdose

Acute Sympathomimetic Toxidrome

The clinical effects are predominantly characteristic of acute sympathomimetic toxicity 3:

• Cardiovascular: Tachycardia, hypertension, chest pain, cardiac dysrhythmias, vasculitis 3
• Neurological: Agitation, psychosis, seizures, headache, cerebral hemorrhage 3
• Thermoregulatory: Hyperthermia 3
• Respiratory: Tachypnea 3
• Behavioral: Violent and aggressive behavior 3

Severe Complications

• Cardiac dysrhythmia leading to sudden death 1
• Excited delirium syndrome 1
• Cerebrovascular accidents 3
• Acute renal dysfunction 5
• Psychosis and other mental disorders 5

Management Principles

Emergency stabilization and supportive care are essential, with benzodiazepines as first-line treatment for most sympathomimetic manifestations. 3

Primary Treatment Approach

• Benzodiazepines alone may adequately relieve agitation, hypertension, tachycardia, psychosis, and seizures 3
• Symptom-directed supportive care for specific complications 3
• Continuous monitoring of vital signs and cardiac rhythm 3

Specific Interventions

• Hyperthermia: Aggressive cooling measures 3
• Hypertension/tachycardia: Benzodiazepines first-line; consider additional antihypertensives if refractory 3
• Seizures: Benzodiazepines; escalate to other anticonvulsants if needed 3
• Psychosis/agitation: Benzodiazepines; antipsychotics may be required for severe cases 3

Prognosis

With appropriate symptom-directed supportive care, patients can be expected to make a full recovery, even from massive overdoses. 3, 2 The case of survival after 2.3 grams IV demonstrates that aggressive supportive care can be life-saving even in extreme overdoses 2.

Important Caveats

• No safe threshold exists: Any dose can be dangerous, particularly in naive users or those with cardiovascular disease 3, 1
• Polysubstance use dramatically increases risk: The fatal case involved co-ingestion of tramadol, lorazepam, and cannabis 1
• Time to death varies: The fatal case involved death approximately 12+ hours after ingestion, demonstrating delayed toxicity 1
• Blood concentrations are poor predictors: The 30-fold difference between hospital and autopsy blood levels (3.0 vs 30 mg/L) in the fatal case shows ongoing absorption and redistribution 1