Medical cannabis improved quality of life and reduced opioid use in people with substance use disorder | Research

The takeaway

In a UK registry of 34 patients with substance use disorder treated with medical cannabis, quality of life, sleep, and anxiety improved while prescribed opioid doses decreased over six months.

Addiction medicine specialists, harm reduction advocates, and policymakers evaluating medical cannabis for substance use disorder.

What the researchers found

Patients showed improvements in GAD-7 anxiety scores, sleep quality, and EQ-5D-5L quality of life at 1, 3, and 6 months. Prescribed opioid doses (oral morphine equivalent) decreased. 85% were already using illicit cannabis at baseline. Only 3 patients (8.8%) reported 17 adverse events.

Why it matters

If medical cannabis can improve outcomes for people with substance use disorder while reducing opioid requirements, it could represent a harm reduction strategy, though the observational design prevents causal conclusions.

The numbers in context

34 patients, 79.4% male. 85.3% using illicit cannabis at baseline. 52.9% had opioid use disorder. Products: 11.8% oils, 41.2% dried flower, 47.1% combination. 8.8% reported adverse events. Improvements in GAD-7, SQS, and EQ-5D-5L.

How the study worked

Observational analysis of UK Medical Cannabis Registry data for 34 patients with substance use disorder. Outcomes measured at 1, 3, and 6 months using validated patient-reported outcome measures.

What this study cannot tell us

Very small sample (34 patients). No control group or randomization. 85% already using illicit cannabis, so improvements may partly reflect switching to regulated products rather than a new therapeutic effect. Selection bias in who enrolls in a cannabis registry.

How to read the evidence

Small observational study from a patient registry without controls. Provides signal but cannot establish causation.

When this study was published

2025 publication.

The bigger picture

This study reflects a paradigm shift: treating cannabis not as a substance to abstain from but as a regulated medicine that might help people reduce more harmful substance use. The high baseline rate of illicit cannabis use suggests these patients were already self-medicating.

Questions still open

Would randomized controlled trials confirm the opioid-sparing effect of medical cannabis in SUD?
Does switching from illicit to regulated cannabis alone account for the observed improvements?

Common questions

Can cannabis treat opioid addiction?

This small study found associated improvements, but cannot prove causation. The concept of cannabis as opioid substitution therapy is controversial. Most patients were already using illicit cannabis, so the study may primarily show benefits of regulated access over illicit use.

What types of cannabis products were prescribed?

Nearly half received a combination of dried flower and oils, about 41% received dried flower alone, and about 12% received oils only. This reflects real-world prescribing patterns in the UK medical cannabis system.

Read the original research

UK Medical Cannabis Registry: A Clinical Analysis of Patients with Substance Use Disorder.

European addiction research, 31(5), 325-335

View on PubMed ↗Publisher’s paper ↗

Citation

Ghosh, Aishwarya; Erridge, Simon; Coomber, Ross; Bhoskar, Urmila; Holden, Wendy; Kamal, Fariha; Mwimba, Gracia; Sachdeva-Mohan, Simmi; Shaya, Gabriel; Usmani, Azfer; Rucker, James; Sodergren, Mikael. (2025). UK Medical Cannabis Registry: A Clinical Analysis of Patients with Substance Use Disorder.. European addiction research, 31(5), 325-335. https://doi.org/10.1159/000547696