Dextromethorphan

For an informed discussion with your doctor or pharmacist. This information collection is not a clinically validated interaction checker. Missing data do not establish safety. Do not change or stop prescribed medicines on the basis of this information. The findings apply to the specific conditions studied; laboratory and animal studies cannot be directly extrapolated to humans.

Active substance: Dextromethorphan

Examples of brand names: Silomat DMP [DE]

ATC code: R05DA09

Main use (for orientation): Dry cough

Documented research summary

A human crossover probe study showed no CYP2D6 inhibition effect after the specific single administration of CBD-rich / THC extract; this contradicts simply extrapolating in-vitro CYP2D6 inhibition. Urine metabolite study 40738618 mentions THC/DXM, but its abstract provides no pair results: a gap in evaluation / full-text access, not a claimed effect.

Uncertainties and limitations

Revision dated 21 September 2026; not equivalent to the Nuedexta/Auvelity combinations.

Shared enzymes must not be equated with clinical evidence of an interaction; CBD/THC findings cannot be extrapolated to other cannabinoids.

PMID40738618/DOI10.5055/jom.0907: full text with individual THC pair values remains inaccessible; the abstract is insufficient to establish direction or magnitude.

Separately recorded findings

2 separately recorded findings. Each statement applies to its documented study context.

CBD + Δ9-THC (oral extract) – clinically studied

Finding ID: B0025

Type of result: No / minor effect under the conditions studied

Observation: No significant change in dextromethorphan AUC∞, Cmax or half-life in the CBD/THC extract arm. No corresponding CYP2D6 inhibition signal; however, subsequent dextrorphan conjugation changed: dextrorphan glucuronide / dextrorphan AUC ratio −44%, glucuronide formation clearance −55%.

Mechanism: CYP2D6 probe

Study type: Randomised crossover pharmacokinetic study

Context studied: 18 enrolled; dextromethorphan analysis n=16 after excluding two CYP2D6 poor metabolisers; dextromethorphan 30 mg as part of a combined CYP probe cocktail, 30 minutes after CBD-rich plant extract (640 mg CBD + 20 mg THC) in a brownie versus placebo. Double-blind, randomised crossover; at least one week's washout; standardised low-fat breakfast one hour before the brownie; samples over 0–24 h.

Clinical interpretation: Null finding

Limitations and uncertainties: Other exposures remain unresolved.

Original sources for this finding: Evaluation of Cytochrome P450-Mediated Cannabinoid-Drug Interactions in Healthy Adult Participants [CL09]

Δ9-THC (oral extract without CBD) – clinically studied

Finding ID: B0030

Type of result: No / minor effect under the conditions studied

Observation: No corresponding CYP2D6 inhibition signal based on parent dextromethorphan pharmacokinetics in the THC extract arm. However, the dextrorphan / dextromethorphan AUC ratio decreased by 30%; this is not a universal null finding for every metabolite measure.

Mechanism: CYP probe

Study type: Randomised crossover pharmacokinetic study

Context studied: 18 enrolled; dextromethorphan analysis n=16 after excluding two CYP2D6 poor metabolisers; dextromethorphan 30 mg as part of a combined CYP probe cocktail, 30 minutes after THC plant extract (20 mg THC, without CBD) in a brownie versus placebo. Double-blind, randomised crossover; at least one week's washout; standardised low-fat breakfast one hour before the brownie; samples over 0–24 h.

Clinical interpretation: Null finding

Limitations and uncertainties: Single administration; no general assurance of safety.

Original sources for this finding: Evaluation of Cytochrome P450-Mediated Cannabinoid-Drug Interactions in Healthy Adult Participants [CL09]

References and access status

[BWEB09] Benylin Dry Coughs 7.5 mg/5 ml Syrup SmPC

Original source / bibliographic reference

Authors: McNeil Products / emc

Year: 2026

Source type: Regulatory product information / SmPC

Source access – 23 October 2026: Source destination was accessible when checked.

Bibliographic attribution or source identity cross-checked.

[CL09] Evaluation of Cytochrome P450-Mediated Cannabinoid-Drug Interactions in Healthy Adult Participants

Original source / bibliographic reference

Authors: Bansal S; Zamarripa CA; Spindle TR; Weerts EM; Thummel KE; Vandrey RG; Paine MF; Unadkat JD

Year: 2023

Source type: Randomised placebo-controlled crossover probe study

DOI: 10.1002/cpt.2973

PMID: 37313955

Source access – 23 October 2026: Direct retrieval could not be fully verified; availability remains unresolved.

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

PubMed Central – full-text access according to the literature database – Archive attribution confirmed by Europe PMC metadata. Direct retrieval was not fully verified here; access may require a browser check.

Europe PMC – full-text access according to the literature database – Listed as freely available HTML full text in the official Europe PMC metadata. Direct retrieval was not fully verified here.

[BMED35115300] Comprehensive Predictions of Cytochrome P450 (P450)-Mediated In Vivo Cannabinoid-Drug Interactions Based on Reversible and Time-Dependent P450 Inhibition in Human Liver Microsomes.

Original source / bibliographic reference

Authors: Bansal S, Paine MF, Unadkat JD.

Year: 2022

Source type: Primary publication; abstract reviewed

DOI: 10.1124/dmd.121.000734

PMID: 35115300

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

PubMed Central – archived text

DOI – publisher access (access restrictions may apply)

[BMED21821735] Cannabidiol, a major phytocannabinoid, as a potent atypical inhibitor for CYP2D6.

Original source / bibliographic reference

Authors: Yamaori S, Okamoto Y, Yamamoto I, Watanabe K.

Year: 2011

Source type: Publication; title and abstract reviewed

DOI: 10.1124/dmd.111.041384

PMID: 21821735

Source access – 23 October 2026: Automated direct retrieval was restricted; this does not establish that the link is broken.

Bibliographic attribution or source identity cross-checked.

PubMed – bibliographic reference / abstract

DOI – publisher access (access restrictions may apply)

[CA_P_40738618] Urinary metabolic ratio of pain management and substance abuse treatment drugs: Drug-drug interactions.

Original source / bibliographic reference

Authors: Cua A, Wickett E, Pesce AJ.

Year: 2025

Source type: Journal Article

DOI: 10.5055/jom.0907

PMID: 40738618

Source access – 23 October 2026: Direct retrieval could not be fully verified; availability remains unresolved.

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

Research as of 23 October 2026. Not all original full texts could be reviewed in full. Source accessibility and the strength of scientific evidence must be assessed separately. An accessible link does not establish medical approval; a bibliographic record with an abstract does not replace the original full text.

Drug search and explanation of the evidence · Guide: cannabinoids and medicines · Author and responsibility