[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Cough and cold medicines](https://durgical.com/en/pharmacology/classes/cough-and-cold-medicines/) › Dextromethorphan

# 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.

Updated Nov 1, 2026

## Quick facts

**Group**
[Cough and cold medicines](https://durgical.com/en/pharmacology/classes/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.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## 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) →](https://durgical.com/en/conditions/common-cold/)
- Cough of acute bronchitis (symptom relief only) [Acute bronchitis →](https://durgical.com/en/conditions/acute-bronchitis/)

## Adverse effects

### Common

- Dizziness and drowsiness
- Nausea, vomiting and stomach upset
- Nervousness or restlessness

### Serious (rare, important)

- Serotonin syndrome with MAO inhibitors or other serotonergic drugs
- Misuse at high doses: hallucinations, dissociation, agitation, tachycardia
- Serious effects or death in young children with cough and cold products

## 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

## Memory aid

DM: Don't Mix with MAO inhibitors.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/dextromethorphan/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 3

- [Benzonatate](https://durgical.com/en/pharmacology/benzonatate/)
- [Guaifenesin](https://durgical.com/en/pharmacology/guaifenesin/)
- [Chlorphenamine](https://durgical.com/en/pharmacology/chlorphenamine/)

## Related conditions 2

- [Common cold (acute viral rhinopharyngitis)](https://durgical.com/en/conditions/common-cold/)
- [Acute bronchitis](https://durgical.com/en/conditions/acute-bronchitis/)

[← Back to the class: Cough and cold medicines](https://durgical.com/en/pharmacology/classes/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](https://medlineplus.gov/druginfo/meds/a682492.html) (MedlinePlus (U.S. National Library of Medicine), 2022); [Use Caution When Giving Cough and Cold Products to Kids | FDA](https://www.fda.gov/drugs/safe-use-over-counter-otc-medicines-children/use-caution-when-giving-cough-and-cold-products-kids) (U.S. Food and Drug Administration, 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=R05DA09) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/dextromethorphan/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/dextromethorphan/