Among 301 inpatients with cannabis use disorder, 89.4% were taking at least one drug that could interact with cannabis, with levomethadone, buprenorphine, and morphine posing the most serious interaction risks.
Addiction medicine physicians, pharmacists, and clinicians prescribing opioid substitution therapy to patients who also use cannabis.
What the researchers found
89.4% of inpatients with CUD were taking at least one potentially interacting drug. Levomethadone, buprenorphine, and morphine were the most common drugs involved in potentially serious cannabis-drug interactions. 196 drug-drug interactions were also identified, with 25.5% classified as 'avoid combination' and 74.5% as 'consider therapy modification.'
Why it matters
Patients with cannabis use disorder frequently take medications that interact with cannabinoids, especially opioid substitution therapies. The finding that nearly 9 in 10 patients had at least one potential interaction underscores the need for routine interaction screening in addiction treatment settings.
The numbers in context
301 patient cases (85% male, median age 37). 89.4% (269/301) taking at least one potentially interacting drug. Top serious CDIs: levomethadone, buprenorphine, morphine. 196 DDIs identified: 25.5% 'avoid combination,' 74.5% 'consider therapy modification.' Levomethadone + psychotropic combinations most frequent.
How the study worked
Retrospective analysis of medication charts from 301 inpatient cases with cannabis use disorder on an addiction-specific ward over six years. Cannabis-drug interactions screened via drugs.com classification; drug-drug interactions via UpToDate Lexicomp.
What this study cannot tell us
Retrospective design using a single addiction ward in Germany. Potential interactions identified by databases may not all be clinically significant. Could not assess whether identified interactions actually caused adverse events. Population was predominantly male, limiting generalizability.
How to read the evidence
Systematic medication review with validated interaction databases over a six-year period, though single-site design and inability to confirm clinical impact of identified interactions limit the evidence.
When this study was published
Published 2025, reviewing six years of inpatient records.
The bigger picture
Cannabis is often treated as a low-risk substance, but its metabolic interactions with other drugs are real and underappreciated. In addiction medicine, where patients are often on multiple psychoactive medications, systematic interaction checking should be standard practice, not an afterthought.
Questions still open
- How often these potential interactions lead to actual adverse clinical events
- Whether systematic interaction screening changes prescribing practices and patient outcomes in addiction medicine
Common questions
Why do cannabis and opioid substitution drugs interact?
Should patients on methadone or buprenorphine avoid cannabis?
Read the original research
Drug interactions in a sample of inpatients diagnosed with cannabis use disorder.
Journal of neural transmission (Vienna, Austria : 1996), 132(5), 723-730
Citation
Schulze Westhoff, Martin; Massarou, Christina; Bleich, Stefan; Heck, Johannes; Jendretzky, Konstantin Fritz; Glahn, Alexander; Schröder, Sebastian. (2025). Drug interactions in a sample of inpatients diagnosed with cannabis use disorder.. Journal of neural transmission (Vienna, Austria : 1996), 132(5), 723-730. https://doi.org/10.1007/s00702-025-02884-5
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