Dextromethorphan
Cough and cold medicines
Cough and cold medicines
A non-opioid cough suppressant in many cold products; dangerous with MAO inhibitors and misused at high doses.
Quick facts
- Group
- Cough and cold medicines
- Target
- NMDA glutamate receptor and sigma-1 receptor (cough centre)
- Used for
- Temporary relief of dry · Cough of acute bronchitis
- Key effects
- Dizziness and drowsiness · Nausea
- Monitor
- Cough frequency and character
- ATC
- R05DA09
No doses: the clinician sets them by the current guideline.
Mechanism of action
Dextromethorphan is the d-isomer of a codeine analogue, but it has no analgesic or meaningful opioid action at usual doses. It raises the threshold of the cough centre in the brainstem, probably through NMDA-receptor blockade and sigma-1 receptor actions. It also inhibits serotonin reuptake, which explains serotonin syndrome with MAO inhibitors. CYP2D6 converts it to dextrorphan; at high doses its NMDA effects cause dissociation and hallucinations, which is why it is misused.
- Dextromethorphan reaches the brainstem cough centre
- NMDA and sigma-1 actions raise the cough threshold
- Fewer irritant signals trigger coughing
- At high doses NMDA block causes dissociation
Indications
- Temporary relief of dry, irritating cough from the common cold or flu Common cold (acute viral rhinopharyngitis) →
- Cough of acute bronchitis (symptom relief only) Acute bronchitis →
Adverse effects
Common
- Dizziness and drowsiness
- Nausea, vomiting and stomach upset
- Nervousness or restlessness
Contraindications
- Taking an MAO inhibitor or having stopped one within the last two weeks
- Children under 4 years with over-the-counter cough and cold products
- Caution with productive cough (it can trap secretions) and in asthma
Key interactions
- MAO inhibitors (and within two weeks of stopping them)
- Serotonin syndrome: agitation, fever, rigidity, clonus
- SSRIs and other serotonergic drugs
- Higher risk of serotonin toxicity
- CYP2D6 inhibitors (fluoxetine, paroxetine, quinidine)
- Raise dextromethorphan levels
- Alcohol and sedatives
- Additive drowsiness
What is monitored
- Cough frequency and character
- Signs of serotonin toxicity with interacting drugs
- Signs of misuse in adolescents
Administration and safety
- Oral syrups, liquids, tablets and lozenges, often combined with other ingredients
- Labels marked DM contain dextromethorphan: check every product to avoid duplication
- Liquids are measured with the device supplied, not a kitchen spoon
Pregnancy and breastfeeding
Dextromethorphan has been widely used in pregnancy without a clear signal of harm; combination products with other ingredients need separate review.
Nursing care
- Ask about MAO inhibitors and antidepressants before use
- Teach that a cough lasting more than a week, or with fever, rash or headache, needs medical review
- Keep cough products out of reach of children
Pharmacokinetics
- Absorption
- Well absorbed by mouth
- Metabolism
- Liver, by CYP2D6 to dextrorphan; poor metabolisers have higher levels
- Elimination
- Urine
- Onset and duration
- Within about half an hour, lasting several hours
Test yourself
Think of the answer, then tap the question to see it.
Is dextromethorphan an opioid analgesic?
No; it is a codeine-related isomer with no analgesic or meaningful opioid action at usual doses.
Which interaction of dextromethorphan can cause serotonin syndrome?
MAO inhibitors (including within two weeks of stopping them).
Which enzyme metabolises dextromethorphan?
CYP2D6.
Why is dextromethorphan misused at high doses?
NMDA-receptor blockade causes dissociative and hallucinogenic effects.
Connections
← Back to the class: Cough and cold medicines
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Dextromethorphan: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2022); Use Caution When Giving Cough and Cold Products to Kids | FDA (U.S. Food and Drug Administration, 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.