Dextromethorphan Toxicity

Etiology

Dextromethorphan use and misuse can result in toxicity.[4] A typical maximum daily dose of 120 mg per day is unlikely to produce toxic effects. Unintentional or intentional overdose, particularly when combined with serotonergic or other psychoactive substances, such as alcohol, may potentiate toxicity.

Epidemiology

Dextromethorphan was approved by the US Food and Drug Administration in 1958, with recreational misuse emerging shortly thereafter. In the US, dextromethorphan misuse accounts for approximately 6,000 emergency department visits per year, while America's Poison Centers reported more than 15,000 calls in 2024 involving dextromethorphan, often in combination with other substances.[5] Serious outcomes are uncommon within this cohort, and nearly 20% of exposures occur in children younger than age 5 years, likely due to exploratory ingestion.

Dextromethorphan is frequently combined with antihistamines, pseudoephedrine, and acetaminophen in cough and cold medications, contributing to additional adverse effects in overdose settings. Ethanol is a common coingestant.[6] Illicit extraction of dextromethorphan from cough and cold preparations has been reported using 1- or 2-phase acid extraction techniques involving household products, such as ammonia, lighter fluid, and lemon juice.[7] Intentional overdose involving dextromethorphan also occurs, often in the context of coingested psychiatric medications.

Pathophysiology

Dextrorphan, the active metabolite of dextromethorphan, produces a range of physiologic effects through multiple mechanisms. Similar to ketamine and phencyclidine, dextrorphan antagonizes N-methyl-D-aspartate receptors, resulting in hallucinations, euphoria, dissociation, agitation, and coma. Dextrorphan also functions as a serotonin reuptake inhibitor, although to a lesser extent than dextromethorphan. Both dextrorphan and dextromethorphan inhibit norepinephrine reuptake. These pharmacodynamic properties may result in hypertension, tachycardia, mydriasis, agitation, and serotonin syndrome.[8] Serotonin syndrome may occur after isolated overdose arises, or therapeutic doses of dextromethorphan are combined with serotonergic agents, such as selective serotonin reuptake inhibitors, serotonin norepinephrine reuptake inhibitors, monoamine oxidase inhibitors, cocaine, and tricyclic antidepressants.[9][10] Dextrorphan also demonstrates activity at σ-opioid receptors, contributing to antitussive effects.

Certain dextromethorphan products are formulated as dextromethorphan hydrobromide. Rarely, bromide toxicity may occur, resulting from potentiation of γ-aminobutyric acid channels within the central nervous system (CNS).

Toxicokinetics

Dextromethorphan has an estimated half-life ranging from 2 to 24 hours. Hepatic demethylation via cytochrome P450 2D6, an enzyme with significant genetic polymorphism, contributes to substantial interindividual variability in elimination half-life. High-dose exposure may saturate metabolic pathways, resulting in prolonged elimination. Clinical effects typically occur within 1 to 2 hours, with peak plasma concentrations occurring at approximately 2.5 hours. Immediate-release formulations contain standard adult doses, ranging from 5 to 30 mg, with a maximum recommended dose of 120 mg per 24 hours.[11] Extended-release formulations commonly use a 60-mg adult dose, with a maximum total daily dose of 120 mg per 24 hours. Toxicity correlates with dose, with mild stimulation and euphoria occurring at doses ranging from 100 to 300 mg, and dissociation or coma developing with higher ingestions. Respiratory depression or arrest may arise after massive ingestions. Multiple case reports describe markedly elevated postmortem dextromethorphan concentrations on autopsy.[12]

History and Physical

Attention should be given to obtaining a thorough history, particularly regarding the ingested product, amount ingested, time of ingestion, intent, symptoms, and coingestants. As commonly observed in toxicology, patients may be unable to provide a detailed history due to altered mental status. Witnesses, friends, or family members may provide collateral history. A list of prescribed medications should be obtained to assess for potential drug interactions. Depending on dose and coingestants, dextromethorphan may produce a broad spectrum of clinical effects ranging from mild agitation to psychosis, seizures, and coma. Familiarity with street names for dextromethorphan may also be helpful. Common physical examination findings in patients with dextromethorphan toxicity include the following:

• General: Hyperthermia, diaphoresis, and altered mental status that may range from mild agitation to coma
• HEENT (head, eyes, ears, nose, and throat): Mydriasis or nystagmus that may be horizontal, vertical, or rotary
• Cardiovascular: Tachycardia and hypertension
• Respiratory: Tachypnea or respiratory depression in severe cases
• Neurological: Agitation, confusion, hallucinations, ataxia, increased muscle tone, brisk deep tendon reflexes, ankle clonus, seizures, or coma

An assessment for traumatic injuries should also be performed, as patients with intentional self-harm or altered mental status are at increased risk of trauma and may be unable to provide a history suggesting such injury.[13]

Evaluation

The diagnosis of dextromethorphan toxicity is primarily clinical, supported by characteristic findings, including delirium, hallucinations, tachycardia, mydriasis, prominent nystagmus, and brisk deep tendon reflexes. Clinicians should obtain an electrocardiogram, comprehensive metabolic panel, and serum acetaminophen and salicylate concentrations in cases of intentional ingestion or unclear exposure history. Urine drug testing provides limited utility due to frequent false-positive findings, and confirmed results do not establish active intoxication.

Additional evaluation should include point-of-care blood glucose measurement, as well as determination of creatine kinase and ethanol concentration in serum. Since dextromethorphan toxicity may mimic other toxicologic and nontoxicologic conditions (see Differential Diagnosis), further investigations, such as neuroimaging and lumbar puncture, may be required to exclude alternative diagnoses.

Treatment / Management

Supportive care is sufficient for most patients with dextromethorphan toxicity. Primary management priorities include ensuring airway patency, adequate breathing, effective circulation, and hemodynamic stability. Endotracheal intubation with ventilatory support may be required for airway protection in severe cases. A poison center or medical toxicologist should be consulted in all cases.

Sedation with pharmacologic agents and physical restraints may be required to control agitation, violent behavior, and psychosis associated with dextromethorphan toxicity. Placement in a calm environment, such as a quiet room with dim lighting, may provide additional benefit. Benzodiazepines are 1st-line agents for chemical sedation. Lorazepam 2 to 4 mg intravenous or intramuscular administration is reasonable, with repeat dosing as needed for adequate sedation. Dexmedetomidine may serve as an adjunctive agent in refractory cases. Antipsychotic agents are generally not recommended. Physical restraints, if required, should be used for the shortest duration possible, and continuous struggle against restraints should be avoided due to the risk of severe complications and death.

Gastrointestinal decontamination with activated charcoal is most efficacious in dextromethorphan overdose when administered within 1 hour of ingestion. Activated charcoal administered via the oral route or a nasogastric tube is recommended in the absence of contraindications, including active vomiting or CNS depression. Gastric lavage, whole bowel irrigation, and induced emesis are generally not recommended. Naloxone may reverse respiratory depression and CNS depression associated with dextromethorphan toxicity, although such effects are less common.[14][15](B3)

Hyperthermia associated with dextromethorphan toxicity may indicate severe poisoning or complications such as serotonin syndrome. Hyperthermia management is best directed toward control of psychomotor agitation and may require high-dose benzodiazepines. Active cooling measures, including evaporative cooling, intravenous infusion of cooled fluids, and administration of cooled inspired oxygen, should be considered as temporizing interventions.

Fluid resuscitation is a reasonable early intervention for patients with rhabdomyolysis or acute kidney injury. Hemodialysis may be required in severe cases to prevent further complications.

Dextromethorphan commonly appears in combination with acetaminophen, decongestants, and antihistamines in over-the-counter cough and cold medications. Therefore, assessment should include potential antimuscarinic toxicity or acetaminophen poisoning.[16] A prescription combination product containing dextromethorphan and bupropion is also available. Overdose of this medication places patients at high risk for bupropion toxicity, characterized by seizures and dangerous cardiovascular effects.

Bromism, or bromide poisoning, has been reported following overdose of products formulated as dextromethorphan hydrobromide. A high serum chloride concentration and a negative anion gap may be observed. Clinical effects typically include CNS depression due to bromide activity at γ-aminobutyric acid receptors. Treatment is generally supportive.[17][18]

Patients with inadvertent dextromethorphan ingestions may be discharged if asymptomatic for 6 hours after ingestion, provided concurrent pathology, including acetaminophen poisoning, has been excluded. Patients who are symptomatic, especially those with complications, such as hyperthermia, serotonin syndrome, hypertensive crisis, or rhabdomyolysis, require intensive care unit admission for close monitoring. Individuals with suicidal intent should undergo emergency psychiatric evaluation.

Differential Diagnosis

Dextromethorphan poisoning presents with neurologic, autonomic, and behavioral findings that overlap with multiple other conditions. The following entities should be considered during evaluation:

• Alcohol intoxication
• Amphetamine intoxication
• Anticholinergic poisoning
• Bipolar disorder
• Brain neoplasms
• Cocaine toxicity
• Diphenhydramine toxicity
• Delirium tremors
• Encephalitis
• Hyperthyroidism
• Hypoglycemia
• Hyponatremia
• Hypoxia
• Ketamine toxicity
• Lysergic acid diethylamide (LSD) toxicity
• Malignant hyperthermia
• Methylenedioxymethamphetamine (MDMA) toxicity
• Neuroleptic malignant syndrome
• Serotonin syndrome
• Salicylate poisoning
• Toxic alcohol poisoning
• Trauma (self-induced or accidental)
• Meningitis
• Schizophrenia
• Sepsis
• Serotonin syndrome [19]

Investigation of dextromethorphan toxicity should follow a structured approach that considers overlapping toxicologic, neurologic, metabolic, and psychiatric conditions. Diagnostic accuracy is critical, given the potential for rapid deterioration in several of these differentials.

Prognosis

The prognosis of dextromethorphan poisoning is generally favorable, with most patients recovering with supportive care alone. Severe complications and death may occur in rare cases involving large overdoses or coingestion with other substances. In 2024, America's Poison Centers identified no deaths among over 11,000 cases of isolated dextromethorphan product ingestion.

Complications

Dextromethorphan toxicity may produce a range of severe complications through N-methyl-D-aspartate receptor antagonism, serotonergic excess, and adrenergic stimulation. Some known adverse effects include the following:

• Seizures
• Hypertensive emergency
• Coma
• Serotonin syndrome
• Rhabdomyolysis
• Psychosis
• Respiration depression, potentially leading to apnea
• Trauma

Prevention of adverse outcomes requires early diagnosis, avoidance of further exposure, and close clinical observation. Supportive care tailored to emerging neurologic and autonomic instability minimizes progression to life-threatening complications.