MedicalResearch.com Interview with:
Penny F. Whiting, PhD
School of Social and Community Medicine, University of Bristol
The National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care West at University Hospitals, Bristol NHS Foundation Trust, Bristol UK
Kleijnen Systematic Reviews Ltd, Escrick, York, United Kingdom
MedicalResearch: What is the background for this study? What are the main findings?
Dr. Whiting: Cannabis is one of the most popular recreational drugs – only tobacco, alcohol and caffeine are more popular. It can result in an alteration to mood and a feeling of “high”. An estimated 141 million people use cannabis worldwide – this is equivalent to 2.5% of the world’s population. Cannabis has a long history of use for the relief of a wide variety of medical symptoms. There is evidence of its use for medical purposes going back to early Egyptian times. The pen-ts’ao ching the world’s oldest herbal book includes reference to cannabis as medicine for rheumatic pain, constipation, disorders of the female reproductive system, and malaria amongst others, this herbal book also contains the first reference to cannabis as a psychoactive drug. However, its use is controversial as it has been included as a controlled drug in the United Nations Single Convention on Narcotic Drugs since 1961, and the use of cannabis is illegal in most countries.
Medical cannabis (or medical marijuana) refers to the use of cannabis or cannabinoids (any compound, natural or synthetic, that can mimic the actions of plant-derived cannabinoids) as medical therapy to treat disease or alleviate symptoms. Some countries have legalised medicinal-grade cannabis to chronically ill patients but in others its use remains illegal even for medicinal purposes. Canada and the Netherlands have government run programmes where specialised companies supply quality controlled herbal cannabis. These programmes have been running since 2001 and 2003 respectively. In the US around half of the states have introduced laws to permit the medical use of cannabis; other countries have similar laws.
Kleijnen Systematic Reviews Ltd (see below) were commissioned by the Swiss Federal Office of Public Health to conduct a systematic review for the effects and adverse events of medical cannabis to inform policy decision making. Systematic reviews are studies of studies that offer a systematic approach to reviewing and summarising evidence. They follow a defined structure to identify, evaluate and summarise all available evidence addressing a particular research question. We were asked to focus on the following ten indications which were of particular interest to our commissioners: nausea and vomiting due to chemotherapy, patients with HIV/AIDS, chronic pain, spasticity in patients with multiple sclerosis or paraplegia, depression, anxiety disorder, sleep disorder, psychosis, glaucoma, and Tourette’s syndrome. We only included randomised trials, the most robust design for evaluating the effects of an intervention. We included almost 80 trials (nearly 6500 participants). We had most evidence for chronic pain (28 trials), nausea and vomiting due to chemotherapy (28 trials) and spasticity due to MS or paraplegia (14 trials) with less than five studies included for each of the other indications and none for depression. With the exception of the nausea and vomiting due to chemotherapy population, studies general compared cannabinoids to placebo with only single studies for each indication comparing cannabinoid with an active comparator. In the nausea and vomiting population the majority of studies compared cannabinoids to an active comparator, most commonly prochlorperazine.
Most trials reported greater improvement in symptoms with cannabinoids compared to control groups, however, these did not always reach statistical significance. Cannabinoids were also associated with a greater risk of short term adverse events, including serious adverse events. Common adverse events included dizziness, dry mouth, nausea, fatigue, sleepiness, and euphoria. Overall we found that there was moderate quality evidence to support the use of cannabinoids for the treatment of chronic pain and spasticity and low-quality evidence to suggest that cannabinoids were associated with improvements in nausea and vomiting due to chemotherapy, weight gain in HIV infection, sleep quality, and Tourette syndrome. When determining the quality of the evidence we considered the risk of bias in trials, the consistency of the evidence across the trials, the directness of the evidence (was the trials research question directly applicable to our review question), and the precision of the evidence.