Definition and epidemiology
Drug overdose is the clinical syndrome resulting from excessive exposure to a pharmacologic agent, whether prescription, over-the-counter, or illicit, that produces dose-dependent toxicity. It is classified as intentional (self-harm, suicide attempt, misuse to achieve euphoria) or unintentional (accidental pediatric ingestion, dosing error, unknown potency of illicit drugs).
- Overdose is a leading cause of injury-related death in many high-income countries, with opioids (including fentanyl) driving the majority of fatal overdoses in North America.
- Acetaminophen is one of the most common agents in intentional overdose worldwide and a leading cause of acute liver failure in some countries.
- Pediatric exploratory ingestions are common in children under 5 but are usually low-dose and asymptomatic.
- Polysubstance overdose (e.g., opioid plus benzodiazepine or alcohol) substantially increases mortality risk.
- Naloxone reverses opioid toxidrome: miosis, bradypnea, sedation.
- Order acetaminophen and salicylate levels on every intentional overdose, even if asymptomatic.
- Acetaminophen toxicity can be clinically silent for the first 24 hours.
- Widened QRS on ECG in overdose suggests tricyclic antidepressant toxicity; treat with sodium bicarbonate.
- Fomepizole is first-line for methanol/ethylene glycol poisoning; both cause an elevated anion and osmolar gap.
- Activated charcoal is most effective within 1-2 hours of ingestion and requires a protected airway.
- Flumazenil is generally avoided in unknown or chronic benzodiazepine use due to seizure risk.
- All intentional overdoses require psychiatric evaluation before discharge.
Etiology and risk factors
Common agents
- Opioids (heroin, fentanyl, oxycodone, methadone)
- Acetaminophen (often co-ingested with other analgesics)
- Benzodiazepines and sedative-hypnotics
- Tricyclic antidepressants (narrow therapeutic index, high lethality)
- Salicylates (aspirin)
- Stimulants (cocaine, amphetamines)
- Alcohols (ethanol, methanol, ethylene glycol)
- Antipsychotics, anticonvulsants, cardiac drugs (beta-blockers, calcium channel blockers, digoxin)
Risk factors
- History of substance use disorder or prior overdose
- Psychiatric illness, especially depression or history of self-harm
- Chronic pain with opioid prescriptions
- Access to multiple medications in the household (polypharmacy, elderly caregivers)
- Recent release from incarceration or detox (loss of opioid tolerance)
- Use of illicit drugs adulterated with fentanyl or other potent agents
Pathophysiology
Toxicity results from the drug's pharmacologic action exceeding the therapeutic window, saturating metabolic pathways, or producing direct organ injury.
- Opioids: agonism at mu-opioid receptors in the brainstem causes respiratory depression, sedation, and miosis.
- Acetaminophen: at toxic doses, glucuronidation/sulfation pathways are saturated, shunting metabolism through CYP2E1 to form NAPQI, which depletes glutathione and causes hepatocyte necrosis.
- Tricyclics: sodium channel blockade causes QRS widening and ventricular arrhythmia; anticholinergic and alpha-blocking effects add to toxicity.
- Salicylates: uncouple oxidative phosphorylation and directly stimulate the respiratory center, producing a mixed respiratory alkalosis and metabolic acidosis.
- Sedative-hypnotics: potentiate GABA-A receptor activity, causing CNS and respiratory depression.
- Toxic alcohols: metabolized to toxic acid metabolites (formic acid from methanol, glycolic/oxalic acid from ethylene glycol) causing anion-gap metabolic acidosis and end-organ damage (retina, kidney).
Clinical features
Presentation depends on the agent, but recognizing a toxidrome narrows the differential quickly.
| Toxidrome | Vitals/Pupils | Key features |
|---|---|---|
| Opioid | Bradypnea, miosis, hypotension | Sedation, decreased bowel sounds |
| Sympathomimetic | Tachycardia, hypertension, mydriasis | Agitation, diaphoresis, seizures |
| Anticholinergic | Tachycardia, hyperthermia, mydriasis | Dry flushed skin, urinary retention, delirium |
| Cholinergic | Bradycardia, miosis | Salivation, lacrimation, diarrhea, muscle fasciculations |
| Sedative-hypnotic | Normal/low vitals | Slurred speech, ataxia, CNS depression without miosis |
- Nonspecific early signs: nausea, vomiting, drowsiness, confusion.
- Acetaminophen overdose may be clinically silent for 24 hours before transaminitis develops.
- Salicylate toxicity: tinnitus, tachypnea, vomiting.
- Tricyclic overdose: widened QRS, hypotension, seizures, coma ("3 Cs": coma, convulsions, cardiotoxicity).
Diagnosis
Diagnosis is largely clinical, supported by targeted labs and ECG; a specific drug level is only occasionally confirmatory.
- History: ask about substances available, time of ingestion, co-ingestants, suicidal intent; collateral history from family/EMS is essential.
- Vital signs and exam: assess airway, breathing, circulation; pupil size, skin findings, bowel sounds.
- Universal labs: acetaminophen and salicylate levels (ordered on essentially every intentional overdose, since both can be clinically silent), basic metabolic panel, glucose, ECG.
- Additional testing as indicated: osmolar and anion gaps (toxic alcohols), ethanol level, urine toxicology (limited utility, does not change acute management in most cases), ABG, liver function tests, creatine kinase.
- ECG: QRS and QTc prolongation suggest tricyclic or other sodium/potassium channel-blocking agents.
- Poison control center or regional toxicology consultation should be used liberally for agent-specific guidance.
Differential diagnosis
- Primary CNS event (stroke, intracranial hemorrhage, seizure/postictal state)
- Hypoglycemia
- Sepsis or CNS infection (meningitis, encephalitis)
- Metabolic derangement (hepatic encephalopathy, uremia, severe electrolyte disturbance)
- Psychiatric catatonia or primary psychosis
- Alcohol intoxication or withdrawal
- Traumatic brain injury (especially if found down and unwitnessed)
Management
Management follows the standard toxicology approach: stabilize, decontaminate, give antidote if available, and support until the drug is eliminated.
Initial stabilization
- Airway, breathing, circulation first; intubate for airway protection if GCS is low or airway reflexes are lost.
- Continuous cardiac and pulse oximetry monitoring, IV access.
- Check glucose immediately in any altered patient.
Decontamination
- Activated charcoal may be considered within 1-2 hours of ingestion for appropriate agents in a cooperative, airway-protected patient; not used for most hydrocarbons, alcohols, or corrosives.
- Whole bowel irrigation is reserved for specific scenarios (e.g., sustained-release iron, body packers).
- Gastric lavage is rarely used and not routinely recommended.
Antidotes (agent-specific)
- Opioids: naloxone
- Acetaminophen: N-acetylcysteine (based on the Rumack-Matthew nomogram when ingestion time is known)
- Benzodiazepines: flumazenil (rarely used due to seizure risk in mixed overdose or dependence)
- Tricyclics: sodium bicarbonate for QRS widening/arrhythmia
- Beta-blockers: glucagon
- Calcium channel blockers: calcium, high-dose insulin-euglycemia therapy
- Digoxin: digoxin-specific antibody fragments (digoxin immune Fab)
- Methanol/ethylene glycol: fomepizole (or ethanol if fomepizole unavailable), hemodialysis for severe cases
- Organophosphates: atropine, pralidoxime
Supportive and enhanced elimination
- IV fluids for hypotension, benzodiazepines for agitation or seizures, cooling for hyperthermia.
- Hemodialysis for select toxins that are dialyzable, small, water-soluble, and have low protein binding (e.g., salicylates, toxic alcohols, lithium, severe methanol/ethylene glycol toxicity).
- Psychiatric evaluation before discharge for all intentional overdoses; social work and substance use disorder treatment referral (including offering naloxone kits and medication for opioid use disorder) for unintentional opioid overdose.
- International guidelines (WHO, American College of Medical Toxicology, European toxicology societies) broadly agree on this stabilize-decontaminate-antidote-support framework; specific thresholds for interventions like NAC initiation or dialysis vary slightly by regional protocol.
Complications and prognosis
- Aspiration pneumonia from vomiting with decreased consciousness.
- Hypoxic brain injury from prolonged respiratory depression.
- Acute liver failure (acetaminophen) or acute kidney injury (toxic alcohols, rhabdomyolysis).
- Cardiac arrhythmia and cardiac arrest (tricyclics, cardiac glycosides, QT-prolonging agents).
- Rhabdomyolysis from prolonged immobility or seizures.
- Prognosis is generally good with prompt recognition and treatment; delayed presentation (especially for acetaminophen) worsens outcomes.
- Recurrence risk is high without addressing the underlying psychiatric illness or substance use disorder; overdose survivors are at elevated risk of future fatal overdose, particularly in the weeks following an opioid overdose.
DUMBELS for cholinergic toxidrome: Diarrhea, Urination, Miosis, Bradycardia, Emesis, Lacrimation, Salivation.
Practice questions
1. A 22-year-old woman is brought to the emergency department after being found unresponsive next to an empty bottle of acetaminophen tablets, ingested approximately 2 hours ago. She is awake, mildly nauseated, and has no other symptoms. Vital signs are normal. Which of the following is the most appropriate next step?
2. A 35-year-old man with a history of depression is brought in after ingesting an unknown number of amitriptyline tablets. He is lethargic with a blood pressure of 85/50 mmHg. ECG shows a QRS duration of 140 ms. Which of the following is the most appropriate immediate treatment?
3. A 19-year-old man is found unconscious at a party. On exam, respiratory rate is 6/min, pupils are 1 mm bilaterally, and he does not respond to sternal rub. After administration of an appropriate reversal agent, his respiratory rate improves to 14/min and he becomes more alert. Thirty minutes later, he again becomes somnolent with a respiratory rate of 7/min. What is the most appropriate explanation and next step?
Frequently asked questions
What is the most common cause of fatal drug overdose?
Opioids, particularly those involving illicitly manufactured fentanyl, are the leading cause of fatal drug overdose in North America. Prescription opioids, heroin, and fentanyl-adulterated street drugs all contribute, and risk rises sharply when opioids are combined with benzodiazepines or alcohol, which compound respiratory depression.
What are the first signs of a drug overdose?
Early signs depend on the drug but commonly include drowsiness, confusion, nausea, and vomiting. Opioid overdose typically shows pinpoint pupils, slow or shallow breathing, and sedation, while stimulant overdose causes agitation, rapid heart rate, and high body temperature. Any sudden change in alertness or breathing after drug exposure warrants emergency evaluation.
How is a drug overdose diagnosed?
Diagnosis is based on history, physical exam findings (toxidrome pattern), and targeted laboratory testing. Acetaminophen and salicylate levels are checked routinely in intentional overdoses because both can be silent early on, and an ECG is obtained to screen for cardiotoxic agents. Urine toxicology screens have limited value since they rarely change acute management.
Is drug overdose reversible or curable?
Many overdoses are fully reversible with prompt treatment, especially when an antidote exists, such as naloxone for opioids or N-acetylcysteine for acetaminophen given early. Outcomes depend heavily on the agent, dose, time to treatment, and whether organ damage (liver, brain, heart) has already occurred before intervention.
Opioid overdose vs sedative-hypnotic overdose — what is the difference?
Opioid overdose characteristically causes miosis (pinpoint pupils) along with respiratory depression, and responds rapidly to naloxone. Sedative-hypnotic (e.g., benzodiazepine) overdose causes similar CNS and respiratory depression but typically without miosis, and does not reliably reverse with naloxone, requiring supportive airway management instead.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: T36
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.