This page respects the original work's rights terms and independently introduces its bibliography, abstract, main results, and limitations. It is not a full translation.
About this resource
This page introduces a systematic review of randomized trials comparing medical cannabis or cannabinoids with placebo or other controls in adults with chronic non-cancer or cancer-related pain. It included 32 trials with 5,174 participants and evaluated pain, physical functioning, sleep, emotional functioning, quality of life, and adverse events.
The interventions were not a single product. They included oral preparations, oromucosal sprays, inhaled cannabis, and preparations with different THC-to-CBD ratios. Average results therefore cannot be applied directly to a specific commercial product. The authors examined not only whether an effect existed, but also the difference between the number of people who achieved an improvement meaningful to patients and the number who experienced harms.
Study design
The authors searched multiple databases for randomized clinical trials in adults with chronic pain. Results were pooled in meta-analyses, and certainty of evidence was assessed. Many interventions were added to existing treatment, and follow-up was predominantly short to intermediate term.
Causes of pain varied and included neuropathic pain, pain related to multiple sclerosis, and cancer-related pain. Standardization and the “minimally important difference” were used to combine different scales and preparations, but an average difference does not directly represent each patient’s experience.
Content
In chronic-pain research, a statistically detectable difference needs to be distinguished from an improvement meaningful in everyday life. In addition to pain relief, the review examined physical functioning, sleep, emotional and role functioning, and quality of life, while presenting adverse events such as dizziness, somnolence, nausea, and impaired attention in parallel.
Trials of medical preparations did not evaluate the entire cannabis plant or products of unknown composition. Research participants were selected, and administration, records, and stopping criteria were controlled.
Results
Compared with placebo, non-inhaled medical cannabis or cannabinoids may produce a small increase in the proportion of people experiencing pain relief and small improvements in sleep and physical functioning. Transient adverse events including dizziness, somnolence, nausea, and impaired attention increased. Effect sizes were generally small, and certainty of evidence differed among outcomes.
Short randomized trials cannot adequately assess long-term serious harms, dependence, or effects on cognition and mental health. An average improvement in pain scores does not necessarily mean sustained recovery in work, activity, or life as a whole.
Limitations
There was substantial heterogeneity in preparations, routes of administration, THC and CBD composition, pain conditions, comparison conditions, and follow-up periods. Many studies were short, making rare adverse events, tolerance, dependence, and long-term function difficult to assess. Psychoactive effects may also reveal allocation and functionally undermine blinding.
Findings cannot be generalized to people with comorbidities who are difficult to include in clinical trials, older adults, pregnant people, or people using multiple sedating medications. Publication bias and the influence of industry funding also need to be reviewed study by study.
Safety
The review does not provide grounds to replace chronic-pain care with cannabis by oneself or to stop existing medication abruptly. Somnolence, dizziness, and impaired attention relate to the risk of falls, driving, and machinery operation. Combinations with sedatives, alcohol, anticoagulants, and other substances or medications require individual review.
This page does not guide methods of use or product selection. It needs to be read against the original source and the clinical context as evidence showing small average benefits and increased adverse events at the same time.
Source and rights
Original source: Wang L, et al. Medical cannabis or cannabinoids for chronic non-cancer and cancer related pain: a systematic review and meta-analysis of randomised clinical trials. BMJ. 2021;374:n1034. DOI: 10.1136/bmj.n1034.
Respecting the original article’s rights conditions, this page is a detailed introduction that independently summarizes study design, principal results, and limitations from public bibliographic information and the abstract. It is not a full translation or republication of figures and tables.