Dextromethorphan

The biggest hidden danger is combination products: DXM is often sold with acetaminophen (liver toxicity), antihistamines, or decongestants that become dangerous at the doses people take for effect, so only single-ingredient DXM is even remotely safer. Because DXM is serotonergic, combining it with MAOIs, SSRIs, or other serotonergic drugs can trigger serotonin syndrome, which is a medical emergency. High doses cause heavy dissociation, vomiting, rapid heartbeat and impaired coordination, and it should not be stacked with other depressants. Not medical advice.

Dextromethorphan is extensively metabolized via the cytochrome P450 CYP2D6 isoenzyme, making it susceptible to metabolic interactions. Coadministration with potent CYP2D6 inhibitors including fluoxetine, paroxetine, and bupropion significantly prolongs dextromethorphan's half-life and elevates plasma concentrations. ^{[10] [11]} Bupropion combined with dextromethorphan (marketed as Auvelity) deliberately exploits this pharmacokinetic synergy; the CYP2D6 inhibition from bupropion maintains therapeutic dextromethorphan levels, allowing lower oral dosing than would otherwise be achievable. ^[12] Clinicians should monitor for increased adverse effects, including dissociation and dizziness, when dextromethorphan is used alongside other CYP2D6 inhibitors.

Serotonergic agents pose an additional concern given dextromethorphan's NMDA receptor antagonism and sigma-1 receptor activity; this combination warrants careful observation for signs of altered mood or cognition.

Checking a whole stack? Run it through interactions + stacks.