DXM + MAOIs
DXM + MAOIs: the short answerThis combination has killed people at ordinary cough-syrup doses — it is one of the clearest 'never do this' pairs in pharmacology. Serotonin syndrome can start within hours and escalate fast.
Why it’s dangerous
DXM pushes serotonin into the synapse while MAOIs disable the enzyme that removes it, so serotonin accumulates uncontrollably. Because irreversible MAOIs keep working for about two weeks after the last dose, the danger window extends well beyond the day someone last took their medication.
What happens
- Rapid-onset serotonin syndrome: agitation, sweating, vomiting
- Very high fever, rigid and jerking muscles
- Dangerous blood-pressure elevation
- Seizures, coma, and documented deaths
Warning signs
- Confusion and tremor within hours of the DXM dose
- Fever climbing past ~38.5°C/101°F
- Severe headache, pounding heart, or seizure
What to do
- Call emergency services immediately and name both drugs
- No further doses of anything; keep the person cool
- On an MAOI? Avoid all dextromethorphan products — check cough/cold labels carefully
- The rule holds for ~2 weeks after stopping an MAOI (and before starting one after DXM use)