Monika Halicka, Francesca Spiga, and Jelena Savović from the Bristol Evidence Synthesis Group identify four priorities for research into cannabis use disorder.
In December 2025, the Office for National Statistics released its latest figures on drug use in England and Wales. Over the past decade, the prevalence of cannabis use has remained stable but high. An estimated 2.2 million people (6.5% of adults aged 16–59) reported using cannabis in 2024 to 2025. The numbers of people reporting signs of dependence on cannabis have been steadily rising in England, from 2.8% in 2014 to 4.3% in 2024. We have also seen more people coming forward for treatment. Of the adults starting treatment in 2024 to 2025, one in five had a problem with cannabis, and cannabis was the most common substance (86%) that children and adolescents came to treatment for.
These statistics are a timely reminder that cannabis use – often perceived as relatively harmless – can cause real difficulties for some people, who then often face limited treatment options. For researchers, clinicians, and policymakers, the statistics are also an opportunity to reflect on how well we understand this growing issue, and how effectively we’re responding to it.
An overlooked and growing problem
Cannabis remains the most commonly used drug in the UK. While many people use it regularly without major problems, some develop patterns of use that cause distress or interfere with daily life. For example, they may have difficulty controlling their use, start neglecting their responsibilities, or experience withdrawal symptoms when they try to cut down.
‘Cannabis use disorder’ is the clinical term for this pattern of harmful or dependent use. It is a condition that can affect relationships, work, and physical wellbeing, and lead to major mental health problems. Yet, compared with other substance use disorders, cannabis use disorder often receives less attention – in part because of ongoing debates about cannabis’ legal status and its perceived risks.
Recent reports, including the UK Government’s review of drugs, have highlighted the rising burden of cannabis use disorder and the urgent need for effective, evidence-based treatments.
What do we know about treatment options?
According to current UK clinical guidelines, there are no approved pharmacological (drug-based) treatments for cannabis use disorder. Psychosocial interventions, such as talking therapies, remain the recommended first-line options. However, the evidence supporting even psychosocial approaches is surprisingly thin. While the evidence suggests some benefits to psychosocial interventions as a whole, it is still unclear which types of therapy work best and for whom, or which outcomes matter most to people seeking help.
To address some of these questions, the Bristol Evidence Synthesis Group was commissioned by the Department of Health and Social Care to conduct two large systematic reviews and meta-analyses: one on psychosocial interventions, and one on pharmacological treatments. We brought together all the available ‘randomised controlled trials’, which compare treatments in the most unbiased way possible and offer the most trustworthy evidence compared with other study designs. Through aggregating the evidence, we were able to assess the effectiveness and safety of different approaches and highlight where research gaps remain.
These reviews revealed a complex picture. Psychosocial therapies like cognitive-behavioural and acceptance-based interventions show potential benefits, compared with minimal support. Adding a system of rewards for staying off cannabis or showing up for treatment sessions (contingency management), may also help. For pharmacological treatments, even though several classes of drugs have been tested, each has only been studied in few trials, with mixed results. This means that no drug can currently be recommended for treating cannabis use disorder.
Unfortunately, what this means is that the evidence for both psychosocial and pharmacological treatments remains uncertain, mainly because existing studies are small and their results are inconsistent or have methodological limitations. And while there are some encouraging findings supporting psychosocial approaches, the research base is still too limited to draw firm conclusions about which interventions work best.
The problem of measuring ‘success’
One of the biggest challenges in cannabis use disorder research lies not just in the treatments themselves, but in how we measure their effectiveness.
Across clinical trials for cannabis use disorder, researchers use a wide variety of outcomes: from self-reported days of cannabis use or its quantities, to biochemical tests for abstinence, to scores on psychological scales. Even the same outcomes tend to be measured with different instruments, in different units (e.g. number of grams, joints, or inhales), or using different thresholds (e.g. level of cannabis metabolites in urine). This makes it extremely difficult to compare results or combine findings across studies in a meaningful way.
So, if every study measures success differently, how can we tell which treatment really works best? A promising way forward would be to establish a ‘core outcome set’ – a standardised group of outcomes that all future trials should measure. This approach has already improved research consistency in other areas of health, from chronic pain to depression. For cannabis use disorder, some researchers have suggested what such an assessment toolkit might include, but there’s still a need for broader expert and stakeholder consensus.
Abstinence isn’t the only goal
Traditionally, abstinence (complete cessation of cannabis use) has been the most common yardstick for success in cannabis use disorder trials. On paper, it’s a clear, measurable target. But in practice, it’s a very difficult outcome to achieve and sustain.
Importantly, abstinence may not always reflect what people actually want from treatment. Many people seeking help for cannabis-related problems may prefer to reduce use rather than stop completely. From a harm reduction perspective, cutting down can still lead to meaningful improvements in mental health, functioning, and quality of life.
Whether we focus on abstinence, reduced frequency of use, or improvements in wellbeing, there’s no universal agreement on what constitutes a ‘clinically meaningful’ change. How much does someone need to cut down before we can say a treatment has worked? And who should decide what counts as success: researchers, clinicians, or people with lived experience? These questions directly affect how we design clinical trials, how we interpret their findings, and ultimately how we support people seeking help.
Bridging the evidence gap
As interest in cannabis policy reform continues to grow, both in the UK and internationally, the need for robust evidence on prevention and treatment is becoming more urgent. More people are using high-potency cannabis products, and more people who use cannabis are reporting symptoms consistent with dependence. Yet, the science of how best to help them is still catching up.
Our recent reviews highlight several priorities for future research:
- Consistency in measurement: agreeing on a core outcome set for cannabis use disorder trials would make it easier to compare and combine findings
- Broader definitions of success: recognising that reduced use and improved wellbeing can be meaningful treatment goals
- Better understanding of individual differences: not everyone responds to treatment in the same way; personalising approaches could improve outcomes
- Continued investment in psychosocial interventions: pharmacological options remain limited, but psychosocial therapies show promise
Looking ahead
As researchers, practitioners, and policymakers, we have a responsibility to ensure that support for people with cannabis use disorder is grounded in the best possible evidence. That means continuing to refine our understanding of what works, for whom, and how success should be defined.
The good news is that momentum is building. With growing recognition of cannabis use disorder as a genuine public health concern, and with new research efforts underway, we are moving closer to a more coherent and compassionate response – one that reflects both the science and the lived experience of those affected.
Monika Halicka is a Senior Research Associate in Evidence Synthesis at the University of Bristol and a systematic reviewer in the Bristol Evidence Synthesis Group.
Francesca Spiga is a Research Fellow in Research Synthesis and a systematic reviewer of the Bristol Evidence Synthesis Group.
Jelena Savović is Associate Professor of Epidemiology and Evidence Synthesis at the University of Bristol and Knowledge Mobilisation Lead for the Bristol Evidence Synthesis Group.
Declaration of interest: The authors are funded by the National Institute for Health and Care Research (NIHR) Evidence Synthesis Programme. The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care.
The Bristol Evidence Synthesis Group is one of nine, UK-based, research groups commissioned by the NIHR Evidence Synthesis Programme (ESP) to identify, appraise, and combine existing research to answer questions of importance to policymakers and practitioners. The group’s aim is to produce high-quality evidence syntheses that are relevant and useful to the end-user and appropriate to all populations to whom the findings will be generalised. Commissioned projects cover a range of healthcare, public health and social care topics, and draw on the team’s extensive expertise in review methods, including systematic reviews, living reviews, prospective meta-analyses, realist reviews, overviews of reviews, scoping reviews, rapid reviews and ultra-rapid reviews.
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