Cannabis Users Need More Propofol, But Confounders Cloud the Evidence

A meta-analysis of eight observational studies finds cannabis users require approximately 47 mg more propofol than non-users, but the absence of randomized trials and inadequate adjustment for younger age, higher tobacco use, and substantial study heterogeneity prevent confident causal attribution to cannabis exposure alone.

Why This Matters

Cannabis use among surgical and procedural patients has risen sharply in the wake of expanding legalization, and anesthesiologists increasingly report clinical impressions that these patients are harder to sedate. Propofol is the most widely administered intravenous anesthetic worldwide, making even modest dosing shifts clinically and safety-relevant. Quantifying whether cannabis users genuinely require more propofol, and by how much, is essential for perioperative planning. This meta-analysis represents the first formal attempt to pool the available data, arriving at a time when clinicians need evidence-based guidance rather than anecdote.

Clinical Summary

Cannabis use has been hypothesized to increase anesthetic requirements through several plausible but incompletely characterized mechanisms, including cross-tolerance at gamma-aminobutyric acid (GABA) receptors where both THC and propofol exert sedative effects, and potential induction of cytochrome P450 enzymes that metabolize propofol. This PROSPERO-registered systematic review and meta-analysis, reported in accordance with PRISMA guidelines, searched eight major databases through November 2023, screening 2,537 unique references and ultimately including eight observational studies encompassing 2,268 patients. The authors used a DerSimonian and Laird random-effects model to pool mean differences in propofol dose between cannabis users and non-users, with subgroup analyses separating general anesthesia from endoscopic sedation contexts.

The pooled analysis found that cannabis users required approximately 47.33 mg more propofol than non-users overall, with a subgroup estimate of roughly 30.57 mg additional under general anesthesia and 53.02 mg additional during endoscopic sedation. However, cannabis users across the included studies were systematically younger and more likely to smoke tobacco, both of which are independent predictors of higher propofol requirements that were not adjusted for in the pooled estimates. Heterogeneity across studies was notable, and with only eight studies in the final pool, subgroup analyses are statistically fragile. The authors acknowledged these limitations explicitly and called for randomized controlled trials, standardized outcome definitions, and mechanistic research before clinical dosing protocols should change.

Dr. Caplan’s Take

This is exactly the kind of question I get from patients who use cannabis regularly and are scheduled for a colonoscopy or surgery: “Will my cannabis use mean I need more anesthesia?” The honest answer right now is that we suspect yes, but we cannot be certain how much of the observed difference is attributable to cannabis itself versus the fact that cannabis users in these studies were younger and smoked more tobacco. The mechanistic story linking THC to GABA receptor cross-tolerance is biologically reasonable, but none of the included studies actually tested it. That gap between plausible mechanism and proven clinical effect is where overconfidence becomes dangerous.

In my practice, I counsel patients that cannabis use may affect their sedation experience and that full disclosure to their anesthesia team is important. I do not recommend patients stop cannabis abruptly before procedures, as withdrawal dynamics are poorly understood in this context. What I emphasize is transparency with the anesthesia provider, who can titrate accordingly. The evidence supports clinical awareness and individualized vigilance, not a blanket dosing protocol change.

Clinical Perspective

This meta-analysis sits early in the research arc for cannabis-anesthetic interactions. It confirms a directionally consistent association that aligns with clinical experience and mechanistic hypotheses, but it does not establish a causal dose-response relationship. The absence of any randomized controlled trial in this space means that all pooled estimates reflect association, not causation. For patient-facing conversations, it is reasonable to note that cannabis use may affect sedation requirements, but clinicians should not cite the 47 mg figure as a precise dosing adjustment. The subgroup finding of a larger effect during endoscopic sedation than general anesthesia is intriguing but is based on very few studies per subgroup and should be treated as hypothesis-generating.

From a pharmacological standpoint, cannabis users who also consume tobacco present a compounded confounding problem, since tobacco independently induces CYP1A2 and other enzymes that may accelerate propofol clearance. Clinicians should document both cannabis and tobacco use in preanesthetic assessments. There are no known dangerous drug interactions between cannabis and propofol per se, but the risk of inadequate sedation during titration is real and carries its own adverse event profile, including patient movement during procedures. The single most actionable recommendation from this evidence is straightforward: ask every patient about cannabis use during preoperative assessment and communicate this information clearly to the anesthesia team so that titration can proceed with appropriate anticipation.

Study at a Glance

Study Type

Systematic review and meta-analysis of observational studies

Population

2,268 patients across 8 studies (cannabis users vs. non-users undergoing procedures requiring propofol)

Intervention

Cannabis use (self-reported or documented; no standardized exposure definition)

Comparator

Non-cannabis users

Primary Outcomes

Mean difference in propofol dose (mg) between cannabis users and non-users

Sample Size

2,268 patients total across 8 included studies

Journal

Not specified in source data

Year

2025

DOI or PMID

PROSPERO registration: CRD42024484145

Funding Source

Not specified in source data

What Kind of Evidence Is This

This is a PROSPERO-registered systematic review and meta-analysis pooling observational studies, reported per PRISMA guidelines and using a DerSimonian and Laird random-effects model. Within the evidence hierarchy, it occupies a position below meta-analyses of randomized controlled trials but above individual observational studies. The single most important inference constraint is that because all included studies are observational and lack randomization, the pooled estimate reflects association rather than causation, regardless of how precisely the statistical aggregation is conducted.

How This Fits With the Broader Literature

Prior individual studies, including work by Twardowski et al. and Fiorini et al., had each suggested higher propofol requirements in cannabis users, but these were limited by small samples and single-center designs. This meta-analysis confirms the directional consistency of that signal across multiple settings and countries, lending modest weight to the hypothesis. It also aligns with broader anesthesiology literature showing that younger patients and tobacco users independently require more propofol, which complicates the cannabis-specific attribution. No prior meta-analysis had attempted this synthesis, making this work novel in scope even if limited in the causal strength of its conclusions. The authors’ call for standardized cannabis exposure definitions echoes a persistent methodological gap across cannabis-medicine research more broadly.

Common Misreadings

The most likely overinterpretation is treating the 47.33 mg pooled estimate as a reliable dosing adjustment that should be applied to cannabis-using patients in clinical practice. This figure is an unadjusted mean difference drawn from heterogeneous observational studies in which cannabis users were younger and smoked more tobacco. Attributing the entire difference to cannabis pharmacology overstates what the evidence supports. A second common misreading would be interpreting the endoscopic sedation subgroup estimate of 53 mg as more robust than the general anesthesia figure; in reality, both subgroup analyses rest on very few studies and are highly sensitive to the characteristics of individual included datasets.

Bottom Line

This meta-analysis provides the first pooled estimate that cannabis users require more propofol, and the direction of the association is consistent and clinically plausible. However, the magnitude of the effect cannot be separated from confounding by age and tobacco use, and all underlying evidence is observational. This work supports heightened clinical awareness and systematic preoperative screening for cannabis use, but it does not justify specific dosing protocol changes. Randomized, confounder-adjusted trials are needed before the field can move from association to recommendation.

References

1. Systematic review and meta-analysis: Cannabis use and propofol requirements. PROSPERO registration CRD42024484145. 2025.
2. Twardowski MA, Link MM, Twardowski NM. Effects of cannabis use on sedation requirements for endoscopic procedures. J Am Osteopath Assoc. 2019;119(5):307-311.
3. Fiorini K, Kluger B, Engeln M, et al. Impact of marijuana use on propofol requirements for procedural sedation. Am J Gastroenterol. 2018;113:S1364-S1365.
4. DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials. 1986;7(3):177-188.
5. Page MJ, McKenzie JE, Bossuyt PM, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. 2021;372:n71. doi:10.1136/bmj.n71.