Dextromethorphan: Central Antitussive Agent
Dextromethorphan (DXM) is a synthetic morphinan derivative and the most widely used non-opioid antitussive worldwide. Unlike codeine, it has no analgesic or addictive opioid properties at therapeutic doses, but acts centrally to suppress the cough reflex.
Available in numerous OTC cough formulations (syrups, lozenges) often combined with guaifenesin, antihistamines, or decongestants. At supratherapeutic doses, DXM is misused for dissociative/psychedelic effects.
Mechanism of Action
DXM acts primarily as an NMDA receptor antagonist and sigma-1 (σ1) receptor agonist. It also acts as a serotonin and norepinephrine reuptake inhibitor at higher concentrations. Cough suppression occurs via suppression of the cough centre in the medulla oblongata without respiratory depression at therapeutic doses.
Indications & Use
Dry, unproductive cough (irritative cough). NOT indicated for productive cough (expectorant cough) — would impair mucus clearance. Short-term symptomatic treatment only; does not treat the underlying cause.
Dosage
Adults: 15–30 mg every 6–8 hours (max 120 mg/day). Children (6–12 years): 7.5–15 mg every 6–8 hours. Not recommended under 6 years. Extended-release formulations: 60 mg every 12 hours.
Side Effects
At therapeutic doses: drowsiness, dizziness, nausea, constipation. At high/toxic doses (abuse): dissociation, hallucinations, ataxia, tachycardia, hypertension, serotonin syndrome. Tolerance and dependence possible with misuse.
Drug Interactions
MAO inhibitors: serotonin syndrome risk — contraindicated. SSRIs/SNRIs: serotonin syndrome. CYP2D6 inhibitors (fluoxetine, paroxetine): increase DXM plasma levels, increasing adverse effects and toxicity risk.
Contraindications
MAO inhibitor use (within 14 days), hypersensitivity, severe hepatic impairment. Caution: productive cough, asthma (not for active bronchospasm), history of drug abuse, children under 6 years.
Frequently Asked Questions
Can dextromethorphan be taken with other cold medicines?
Many cold combination products already contain DXM. Always check ingredient lists to avoid accidental double-dosing. Never combine with MAO inhibitors or SSRIs.
Is dextromethorphan an opioid?
DXM is derived from the opioid morphinan scaffold but has no significant opioid receptor activity at therapeutic doses. It does not cause opioid-type analgesia or respiratory depression, and is not scheduled as an opioid.
Why should DXM not be used for productive cough?
Productive coughs help clear mucus and secretions from the airways. Suppressing this mechanism with DXM in productive cough can lead to mucus retention and worsen respiratory infections.
References
- EMA assessment of dextromethorphan products
- FDA DXM safety communications
- WHO monograph on antitussives
Medical Disclaimer: This information is for educational purposes only and does not replace professional medical advice.