In several published case reports, warfarin has been associated with increases in INR when used in conjunction with THC and CBD, both in oral and inhaled formulations.

Dosing most likely is a factor when predicting an interaction. One case report described a patient on warfarin who added a low dose of oromucosal THC/CBD resulting in no INR fluctuations (Thomas 2022)

THC & CBD inhibition of CYP 2C9 metabolism of S-warfarin (and/or inhibition of CYP 3A4 metabolism of R-warfarin), resulting in higher drug concentrations of warfarin

Hsu et al 2020

Cortopassi 2020 

Damkier et al 2018

Grayson et al 2017

Yamreudeewong et al 2009

Thomas et al 2022

In a systematic review of the literature (through May 2023), there were no human studies identified that support an interaction between cannabinoids and DOACs or other parenteral anticoagulants

Although intestinal absorption of DOACs are mediated by PgP and CBD has been shown to inhibit PgP activity, there are no reports to support an interaction

Smythe et al 2023

In dose-ranging, randomized, controlled trials, serum concentrations of clobazam and its active metabolite (N-CLB) increased beyond the therapeutic range when in combination with high-dose CBD (15-20 mg/kg/day)

N-CLB levels appear to increase at a substantially higher rate than CLB levels. One study of 13 subjects with refractory epilepsy who were taking concomitant CLB and CBD reported elevated CLB and N-CLB levels. The mean increase in CLB was ~60% while the mean increase in N-CLB was ~500%, resulting in a reduction of CLB dosing.

CBD inhibition of CYP 2C19 resulting in decreased metabolism of N-CLB to its inactive metabolite

Geffrey et al 2015

Devinsky et al 2018

Gaston et al 2017

Several studies have published findings indicating that cannabis use is associated with greater requirements of propofol anesthesia for endoscopic procedures. 

In one case-controlled study of 318 subjects undergoing endoscopy, cannabis users required a significantly higher dose of propofol per kg per minute, with daily users more impacted than occasional users. While cannabis exposure appears to be an independent variable, factors such as age, weight, history of respiratory disease, smoking status and procedure duration also must be considered.

A prospective, randomized study of 60 subjects found that doses of propofol required to achieve appropriate bispectral index (BIS) values (a marker of adequate anesthesia prior to laryngeal mask insertion) were no different between cannabis users and nonusers but doses required to insert the laryngeal mask were significantly higher amongst cannabis users.

Propofol used for endoscopy is titrated to effect; however, when used in conjunction with neuromuscular blocking agents for mechanical ventilation, the impact of greater dosing requirements may be more significant.

The mechanism for this interaction is unclear; however, hypotheses include the down-regulation of the CB1 receptor in chronic cannabis users, and competitive agonism/antagonism at the CB1 receptor by phytocannabinoids

Imasogie et al 2021

Twardowski et al 2019

Flisberg et al 2009