Diphenhydramine

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: Diphenhydramine

Examples of brand names: Vivinox Sleep [DE]

ATC code: R06AA02

Main use (for orientation): Sleep disorders; allergies

Documented research summary

A prospective endoscopy cohort found more frequent diphenhydramine use among cannabinoid users; this may reflect tolerance/confounding. Controlled THC combination study 22596206 identified, but its abstract does not separately report the diphenhydramine pair result; no figures invented. Sedation/anticholinergic risk remains label-supported context.

Uncertainties and limitations

Revision 23 November 2021. Do not equate CYP2D6 inhibition with its own elimination being exclusively CYP2D6-dependent.

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

Full text/results table of PMID22596206 for diphenhydramine not yet available; only the design confirmed from the abstract.

Separately recorded findings

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

Cannabinoid use (not standardised) – clinical signals

Finding ID: B0177

Type of result: Prospective observational

Observation: More frequent diphenhydramine administration during oesophagogastroduodenoscopy: adjusted OR 3.04 (95% CI 1.29–7.30); not significant for colonoscopy.

Mechanism: Association with greater sedation requirements

Study type: 419 outpatient endoscopy patients, 3 centres

Context studied: Multi-drug sedation with midazolam/fentanyl/diphenhydramine; self-reported cannabinoid use.

Clinical interpretation: No causal pharmacokinetic evidence; no direct dose recommendation.

Limitations and uncertainties: Confounding/tolerance/procedure differences; not specific to CBD alone.

Original sources for this finding: Baseline Cannabinoid Use Is Associated with Increased Sedation Requirements for Outpatient Endoscopy. [CA_P_36269560]

Cannabis use – clinical signals

Finding ID: B0238

Type of result: Clinical observation – not causal

Observation: Cannabis use was associated with more frequent diphenhydramine use as an adjunct sedative (p=0.0003).

Mechanism: Sedation requirements during endoscopy

Study type: Prospective observational study

Context studied: 976 patients, 210 cannabis users; moderate sedation with several medicines.

Clinical interpretation: Context-specific finding, not a recommendation for use

Limitations and uncertainties: No isolated diphenhydramine pharmacokinetic/pharmacodynamic intervention; confounders and other sedatives.

Original sources for this finding: Marijuana and endoscopy: the effects of marijuana on sedation. [CA_P_38215858]

References and access status

[BWEB06] Diphenhydramine Hydrochloride 50 mg Tablets SmPC

Original source / bibliographic reference

Authors: Flamingo Pharma UK / emc

Year: 2021

Source type: Regulatory product information / SmPC

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

Bibliographic attribution or source identity cross-checked.

[CA_P_36269560] Baseline Cannabinoid Use Is Associated with Increased Sedation Requirements for Outpatient Endoscopy.

Original source / bibliographic reference

Authors: Nasser Y, Biala S, Chau M, Partridge ACR, Yang JY, Lethebe BC, Stinton LM, Cooray M, Cole MJ, Ma C, Chen YI, Andrews CN, Forbes N.

Year: 2024

Source type: Journal Article

DOI: 10.1089/can.2022.0203

PMID: 36269560

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

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

[CA_P_22596206] Does olanzapine inhibit the psychomimetic effects of Δ⁹-tetrahydrocannabinol?

Original source / bibliographic reference

Authors: Kleinloog D, Liem-Moolenaar M, Jacobs G, Klaassen E, de Kam M, Hijman R, van Gerven J.

Year: 2012

Source type: Research Support, Non-U.S. Gov't; Randomized Controlled Trial; Journal Article

DOI: 10.1177/0269881112446534

PMID: 22596206

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

Bibliographic attribution or source identity cross-checked.

DOI – publisher access (access restrictions may apply)

[CA_P_38215858] Marijuana and endoscopy: the effects of marijuana on sedation.

Original source / bibliographic reference

Authors: Kosirog J, Bouvette C, Pannu J, Gondal J, Madhoun M.

Year: 2024

Source type: Journal Article

DOI: 10.1016/j.gie.2024.01.013

PMID: 38215858

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

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