Depression affects millions of people across the United Kingdom. For some, standard treatments work well. For others, finding relief remains a challenge. A new study, published in the Journal of Affective Disorders, examines what happened when patients with difficult-to-treat depression were prescribed medical cannabis. This blog post summarises the research findings. It also explains what the results might mean and, importantly, what they cannot tell us.
What was this study about?
The UK Medical Cannabis Registry was established by Curaleaf Clinic in 2019 to gather real-world data from patients prescribed CBMPs for a range of medical conditions. A previous analysis of the UK Medical Cannabis Registry, published in 2023, found promise in individuals prescribed medical cannabis for depression.
Researchers wanted to better understand what happens over time when people with depression are prescribed medical cannabis. They therefore looked at data collected over two years from patients enrolled in the UK Medical Cannabis Registry.
The study tracked changes in several areas of health and wellbeing. These included mood, anxiety levels, sleep quality, and overall quality of life. Researchers also recorded any adverse events that patients experienced.
What did the researchers measure?
The study used several validated questionnaires. These are standardised tools that help track symptoms consistently over time. Here is what each one measures:
PHQ-9 (Patient Health Questionnaire-9): This asks nine questions about depression symptoms over the past two weeks. Scores range from 0 to 27. Higher scores indicate more severe depression.
GAD-7 (Generalised Anxiety Disorder-7): This measures anxiety symptoms with seven questions. Scores range from 0 to 21. Many people with depression also experience anxiety, so tracking both is useful.
SQS (Single-Item Sleep Quality Scale): A single question asking people to rate their sleep from 0 (terrible) to 10 (excellent).
EQ-5D-5L: A widely used measure of overall health-related quality of life. It covers mobility, self-care, usual activities, pain, and anxiety or depression.
PGIC (Patient Global Impression of Change): This simply asks patients whether they feel better, worse, or the same since starting treatment.
Patients completed these questionnaires at the start of treatment. They then repeated them at 1, 3, 6, 12, 18, and 24 months.
What did the data show?
A total of 698 patients who were prescribed medical cannabis for depression were included in the final analysis. The majority of patients were male (71.35%), with an average age of 37 years.
Patients reported changes across all the measures tracked in the study. These changes appeared within the first month and were maintained over the two-year follow-up period.
Changes in depression scores
At the start of the study, the average PHQ-9 score indicated moderate-to-severe depression. Over time, patients reported lower depression scores on average.
By 24 months, about 62% of patients had experienced what researchers call a “minimal clinically important difference.” This means their improvement was large enough to be considered meaningful, not just a small statistical change.
Changes in anxiety scores
Anxiety was common in this group. At the start, over half of patients reported severe anxiety symptoms on the GAD-7.
The data showed that anxiety scores also decreased over time. By 24 months, around 80% of patients reported a clinically meaningful reduction in anxiety.
Sleep and quality of life
Sleep quality scores improved, though the changes were smaller than those seen for mood and anxiety. Quality of life scores also increased over the study period.
When did changes occur?
The largest improvements appeared in the first three months. After that point, scores remained relatively stable rather than continuing to improve.
Were there any side effects?
About 9% of patients reported at least one side effect during the two-year period.
The most commonly reported side effects were:
- Fatigue
- Difficulty sleeping
- Dry mouth
- Headache
- Lethargy
Most reported side effects (85%) were classified as mild or moderate. Severe side effects were uncommon.
The data suggested that older patients and those taking higher doses of CBD were more likely to report side effects. This is something clinicians consider when tailoring treatment.
What are the limitations of this research?
This is perhaps the most important section of this summary. The researchers themselves were clear about what this study cannot tell us.
No control group: This was an observational study. There was no comparison group of patients who received a placebo or different treatment. This means we cannot know whether the improvements were caused by the treatment itself.
Several other factors could explain the changes patients reported:
Placebo effect: People often feel better when they believe they are receiving helpful treatment. This effect can be particularly strong with medical cannabis due to expectations and positive media coverage.
Hawthorne effect: Simply being observed and monitored in a study can change how people feel and report their symptoms.
Natural fluctuation: Depression symptoms naturally vary over time. Some improvement might have occurred regardless of treatment.
Other life changes: Over two years, many things in a person’s life might change. New relationships, jobs, or other treatments could all play a role.
Self-selected participants: Patients in this study chose to seek out and pay for private treatment with medical cannabis. They may differ in important ways from the broader population of people with depression. They might have been more optimistic about cannabis-based treatment, for example.
Dropout rates: Not everyone completed the full two years of follow-up. People who stopped treatment or stopped responding to questionnaires might have had different experiences. If those who felt worse were more likely to leave the study, this would make the results look more positive than reality.
Self-reported data: All the information came from questionnaires completed by patients themselves. There were no independent clinical assessments or biological markers to verify the findings.
What do these Findings Mean for Patients and Clinicians?
The researchers concluded that the data supports further investigation of medical cannabis for depression. However, they were clear that this study alone cannot establish whether the treatment works.
To answer that question definitively would require randomised controlled trials. These would compare medical cannabis to a placebo under carefully controlled conditions. Such trials are complex to design and conduct, but they remain the standard for establishing treatment effectiveness.
How does someone access medical cannabis in the UK?
Medical cannabis has been legal to prescribe in the UK since November 2018. However, access is limited and involves specific requirements.
A specialist doctor must assess whether medical cannabis is appropriate. This decision involves reviewing your medical history, previous treatments, and current symptoms. The doctor will consider whether you have tried other options first and whether the potential benefits outweigh the risks in your individual case.
Treatment decisions are made jointly between clinician and patient. What works for one person may not be suitable for another. Factors like other medications, health conditions, and personal circumstances all play a role.
If you are struggling with depression, the first step is always to speak with your GP or a mental health professional. They can discuss all available options and, if appropriate, refer you to a specialist. Alternatively, you can choose to self-refer if you prefer.
Where can I learn more?
The full study is available in the Journal of Affective Disorders. The reference is:
Lillywhite E, Erridge S, Clarke E, et al. UK Medical Cannabis Registry: A two-year case series of clinical outcomes in depression. Journal of Affective Disorders. 2025. DOI: 10.1016/j.jad.2025.121130
For general information about depression and treatment options, the NHS website provides helpful resources.
If you are experiencing depression, please speak with a healthcare professional who can discuss all available options with you.
Disclosure: This research was conducted by clinicians at Curaleaf Clinic using data from the UK Medical Cannabis Registry, which Curaleaf Clinic owns and operates. Curaleaf Clinic provided the treatment described in this study. We believe it is important to be open about this when sharing these findings.
