Psilocybin and dextromethorphan
CautionAntitussive, NMDA antagonist, SRI · also: dxm, robitussin, delsym, benylin, nyquil
Psilocybin and dextromethorphan (DXM): normal cough-medicine doses are not the issue; recreational doses add serotonergic and dissociative effects and are a real caution.
At cough-suppressant doses, little. At recreational doses, additive serotonergic load and a confusing, disorienting combination.
Claims re-checked against the cited sources:
Why it happens
DXM is an NMDA antagonist and sigma-1 agonist with serotonergic activity. CYP2D6 is its major metabolic route, so CYP2D6 poor metabolisers (about 7 to 10% of white people) and people on CYP2D6 inhibitors such as fluoxetine or paroxetine reach much higher levels. Serotonin syndrome cases involve high DXM doses plus an SSRI or MAOI, not psilocybin.
What is known
DXM's serotonergic activity is established. Serotonin syndrome cases involving DXM are usually with an SSRI or an MAOI rather than a psychedelic.
- 2026
- DXM is an uncompetitive NMDA antagonist and sigma-1 agonist; CYP2D6 catalyses its major metabolic pathway; about 7 to 10% of Caucasians and 3 to 8% of African Americans are CYP2D6 poor metabolisers. Serotonin syndrome may occur with SSRIs or tricyclics; MAOIs are contraindicated. NUEDEXTA (dextromethorphan/quinidine) US prescribing information, DailyMed (label version Jan 2026)
- 2008
- Two confirmed serotonin syndrome cases involved supra-therapeutic DXM levels with therapeutic SSRI levels; the authors suggest therapeutic DXM doses alone are not enough. Schwartz et al., 'Dextromethorphan-induced serotonin syndrome', Clin Toxicol
- 2026
- DXM toxicity can cause serotonin syndrome, seizures, tachycardia, psychosis and rhabdomyolysis, but DXM has a generally favourable safety profile when used appropriately. Crumlich & Schaffer, 'Dextromethorphan Toxicity', StatPearls (updated Jun 2026)
- 2024
- A 2024 systematic review found no human study of psilocybin with DXM. Halman et al., 'Drug-drug interactions involving classic psychedelics: a systematic review', J Psychopharmacol
Safety guidance
- A normal dose of cough medicine is not the issue.
- Recreational DXM on top of mushrooms is a different and harder experience than either alone; avoid it.
- If you take an SSRI, especially fluoxetine or paroxetine, or an MAOI, avoid recreational DXM entirely.
- Check combination cold products for other ingredients such as pseudoephedrine.
When to seek help
Call emergency services for high fever, muscle rigidity or twitching, a seizure, a very fast heartbeat, or severe confusion or agitation. Emergency red flags.
Common questions
Can I take cough syrup during or after a trip?
At the dose on the label, there is no known problem. The concern is recreational doses.
Why does my antidepressant matter?
Some SSRIs block CYP2D6, raising DXM levels, and SSRIs plus high-dose DXM have caused serotonin syndrome.
Does DXM plus mushrooms cause serotonin syndrome?
No case was found. Published cases involve DXM with an SSRI or MAOI.
How we research this: sources, evidence grading, review and updates.