What is medical cannabis and where is it available?
Medical cannabis has now been legalised in many countries around the world. After decades of prohibition, patients can access medical cannabis on prescription for the management of a wide range of conditions and symptoms. In the UK, medical cannabis has been available on prescription since November 2018.
However, high-quality evidence on the effectiveness and safety of medical cannabis remains limited. Existing systematic reviews have produced mixed findings. While some reviews suggest that medical cannabis may increase the risk of non-serious side effects compared with placebo, they have not been linked to an increased risk of serious side effects. Serious side effects are defined by international clinical practice standards as any unexpected medical occurrence causing death, life-threatening conditions, significant disability, or hospitalisation.
Given the need for more evidence, observational studies can provide valuable insight into patient experiences with medical cannabis. They do this through collecting data from patients in real-world settings rather than in controlled trials.
What did this study investigate?
Medical cannabis has been legal in Denmark since 1st January 2018. The Danish Medicines Agency recommends that physicians may prescribe medical cannabis for painful spasticity caused by multiple sclerosis (MS), painful spasticity due to spinal cord injury, chemotherapy-induced nausea and vomiting, and neuropathic pain. Prescribing is not limited to these conditions, however.
A recent study, published in the Journal of Complementary and Integrative Medicine in December 2025, aimed to build on this evidence base. Researchers at the University of Southern Denmark conducted a nationwide online survey in October–November 2020 to examine patients’ perceived benefits and side effects from medical cannabis use.
Survey respondents were divided into two groups. The first group included patients who received medical cannabis for one or more of the four conditions recommended by the Danish Medicines Agency. The second group included patients who had received medical cannabis for any other condition.
The primary outcome was patients’ perceived benefit from medical cannabis treatment. The researchers also explored reported side effects, including fatigue, negative mood changes, dizziness, concentration difficulties, memory difficulties, and others.
What were the key findings?
A total of 1,044 survey respondents were included in the final analysis. Participants were most commonly female, aged 60 years or above, and had received between one and three medical cannabis prescriptions. Most participants (56%) were past medical cannabis users.
What changes did patients report?
Most patients across both groups (67%) reported perceiving a moderate to large effect from medical cannabis. This perception was slightly more common among patients with conditions outside the four recommended indications (68.7%) than those with the recommended indications (60.8%).
Important context: These are patients’ self-reported perceptions. This study did not use a control group or objective measures of treatment effectiveness. The authors note that the perceived changes reported by patients in this survey are higher than the modest effects typically observed in randomised controlled trials. Self-reported outcomes may be influenced by expectations, the placebo effect, and other factors.
What side effects were reported?
More than half of all patients (55.4%) reported experiencing at least one side effect. This rate was similar across both groups of patients. Between 14% and 15% of patients reported experiencing three or more side effects.
The most commonly reported side effects across both groups were dry mouth (18–27%), fatigue (19–20%), feeling “high” (11–12%), and dizziness (10–12%). When the researchers analysed patterns among these side effects, they clustered into four groups: cognitive dysfunction (including concentration and memory difficulties), dizziness, xerostomia (dry mouth and increased thirst), and feeling “high”.
Notably, the number of side effects experienced was not statistically linked to how much benefit patients perceived. In other words, patients who reported moderate to large benefits were no more or less likely to experience side effects than those who reported little or no benefit.
What were the limitations of this study?
This survey-based analysis offers valuable insight into patients’ perceptions, but there are several important limitations to consider when interpreting these findings.
No control group: Without a control group, the study cannot draw conclusions about the objective effectiveness of medical cannabis. The findings reflect patients’ self-reported perceptions only.
Cross-sectional design: As the study captured responses at a single point in time, it cannot show how perceived benefits or side effects may change over the course of treatment.
Potential bias: Healthy user bias may be present, as survey respondents tend to be healthier than non-respondents. Additionally, recall bias may have influenced responses from past users, who might under- or overestimate their previous experiences.
Missing product information: The study did not record the tetrahydrocannabinol to cannabidiol (THC:CBD) ratio or type of product used by participants, which could have provided important context for understanding the reported side effects.
Self-reported data: Actual prescriptions were not verified, and no information on serious adverse events was collected. The researchers acknowledge that clinical trials would be better suited to investigating the safety profile of medical cannabis products.
Could you be suitable for a medical cannabis consultation?
Medical cannabis has been available on prescription in the UK since 2018. Patients with a wide range of conditions may be eligible for a medical cannabis consultation when other treatments have not been tolerated or have been ineffective at managing symptoms.
Complete our online eligibility assessment today to find out if you could be suitable for a consultation with one of our specialist clinical team. A consultation does not guarantee a prescription and is subject to clinical assessment.
