Drug Interactions

DXM Drug Interactions

Always research any combination independently. This database is for harm reduction reference only — not medical advice. In an emergency call 911.

☠ Deadly ⚠ Dangerous ⚡ Caution ✓ Safe
DXM + MAOIs (phenelzine, tranylcypromine, selegiline)
☠ Deadly
Serotonin syndrome via 5-HT reuptake inhibition + MAOI — can be fatal
Full details
Absolute contraindication. Can cause hyperthermia, seizures, death. Includes moclobemide (reversible). Wait 14 days after stopping MAOI.
DXM + MDMA (ecstasy)
☠ Deadly
Serotonin syndrome — MDMA + DXM both strongly serotonergic
Full details
Particularly dangerous. Both dramatically increase synaptic serotonin. Numerous fatalities documented. Do not combine.
DXM + Alcohol
⚠ Dangerous
CNS depression potentiation; unpredictable dissociative-depressant interaction
Full details
Significantly increases confusion, coordination loss, blackout risk, respiratory depression at higher doses.
DXM + Antihistamines (diphenhydramine, DPH)
⚠ Dangerous
Both anticholinergic. Together: hyperthermia, delirium, tachycardia, urinary retention
Full details
Common combination in OTC products — this is why triple-C (Coricidin) is particularly dangerous. Anticholinergic toxicity at much lower doses than either alone.
DXM + Lithium
⚠ Dangerous
Neurotoxicity risk; DXM may alter lithium excretion; both affect serotonin
Full details
Avoid combination. Lithium users are at elevated seizure and serotonin toxicity risk.
DXM + Opioids (codeine, oxycodone, hydrocodone)
⚠ Dangerous
CNS + respiratory depression. DXM is a weak opioid itself. Combined respiratory risk.
Full details
Avoid. At 3rd/4th plateau DXM has meaningful opioid receptor activity adding to respiratory depression from opioids.
DXM + SNRIs (venlafaxine, duloxetine)
⚠ Dangerous
Dual serotonin syndrome pathway + NRI mechanism
Full details
Similar risk profile to SSRIs. Avoid combination.
DXM + SSRIs (fluoxetine, sertraline, paroxetine)
⚠ Dangerous
Serotonin syndrome risk; SSRIs also inhibit CYP2D6 reducing DXM metabolism → toxic plasma levels
Full details
Fluoxetine and paroxetine are the most dangerous — strong CYP2D6 inhibitors. Sertraline lower risk but still caution. Discontinue at least 2 weeks before.
DXM + Stimulants (amphetamine, cocaine)
⚠ Dangerous
Cardiovascular stress — hypertension, tachycardia, hyperthermia. Serotonin risk with MDMA.
Full details
Significant cardiovascular strain. Combination can precipitate cardiac events. MDMA combination risks severe serotonin syndrome.
DXM + Tramadol
⚠ Dangerous
Serotonin syndrome + seizure risk. Both are weak opioids + serotonergic
Full details
Do not combine. Both lower seizure threshold and act serotonergiclaly.
DXM + Antipsychotics (haloperidol, quetiapine)
⚡ Caution
CYP2D6 interactions; additive CNS depression; may blunt or alter DXM dissociative effects
Full details
Complex interaction profile. Some antipsychotics are CYP2D6 inhibitors raising DXM levels. Others compete for receptor sites.
DXM + Benzodiazepines
⚡ Caution
CNS depression additive. Respiratory depression risk increases with dose
Full details
At therapeutic doses less risky than alcohol but at high DXM doses the combination can dangerously suppress respiration. Use minimal dose if unavoidable.
DXM + Cannabis
⚡ Caution
Unpredictable psychedelic amplification; anxiety and paranoia risk increases substantially
Full details
Many users combine; effects are very dose-dependent. Can dramatically intensify dissociation. Start extremely low if combining.
DXM + Grapefruit juice
⚡ Caution
CYP3A4 inhibition increases DXM plasma levels unpredictably
Full details
Can raise DXM blood levels significantly — what would be a 2nd plateau dose may become 3rd plateau. Avoid day of and day before use.
DXM + Guaifenesin (in many DXM products)
⚡ Caution
Nausea and vomiting at higher doses; no direct interaction with DXM effects
Full details
Many OTC DXM products contain guaifenesin. High doses cause significant GI distress. Use pure DXM HBr products.
DXM + Ketamine
⚡ Caution
Additive dissociative effect — unpredictable depth of dissociation
Full details
Both are dissociatives but different receptor mechanisms. Combined effect is more than additive. Risk of being unable to function or summon help.
DXM + Nitrous oxide
⚡ Caution
Additive dissociative effects — unpredictable intensity
Full details
Both are dissociatives. Combined use dramatically deepens dissociation. Risk of dangerous behavioral disinhibition.
DXM + Caffeine
✓ Safe
No known pharmacological interaction
Full details
No direct interaction. Some users find caffeine counteracts DXM sedation. No documented risk at normal doses.
DXM + Water / hydration
✓ Safe
N/A — good practice
Full details
Stay well hydrated. DXM causes some dehydration. Water reduces some side effects.

Understanding DXM Drug Interactions

DXM interacts with substances through several mechanisms. Understanding the mechanism helps you understand the risk.

Serotonin Syndrome (Most Critical)

DXM inhibits serotonin reuptake (like an SSRI) and also weakly releases serotonin. When combined with other serotonergic drugs — MAOIs, SSRIs, SNRIs, tramadol, or lithium — this can cause serotonin syndrome: a potentially fatal condition characterized by high fever, muscle rigidity, seizures, and rapid heart rate. This is the most dangerous interaction class.

CYP2D6 Inhibitors (Dose-Multiplying)

DXM is metabolized by the enzyme CYP2D6. Drugs that inhibit this enzyme — including fluoxetine (Prozac), paroxetine (Paxil), bupropion (Wellbutrin), and DPH (Benadryl) — dramatically slow DXM metabolism, causing much higher blood plasma levels than expected and effectively multiplying the dose received.

CNS Depressants (Additive)

DXM combined with other CNS depressants — alcohol, benzodiazepines, opioids, GHB — creates additive respiratory and cardiovascular depression. This is especially dangerous because the person may lose consciousness or stop breathing.

Poor Metabolizers

About 5-10% of Caucasians are CYP2D6 poor metabolizers genetically. For these individuals, DXM is significantly more potent than expected at standard doses since they cannot convert DXM to dextrorphan efficiently. If you are a CYP2D6 poor metabolizer, standard recreational doses can be equivalent to much higher doses in extensive metabolizers.