Weeding through new evidence on medical cannabis

By Colleen Donder

While the legalization of cannabis in Canada has made the drug more accessible, there are still important pieces of information that people should consider when trying cannabis for medical purposes. Like alcohol and tobacco, cannabis comes with its own risks, and it may not be the answer for all medical problems.

CADTH — an independent agency that finds, assesses, and summarizes the research on drugs and medical devices — wrote a Hospital News article in January 2018 on the medical cannabis evidence available at that time. Since then, CADTH has continued to look for emerging evidence on medical cannabis for treating symptoms of various medical conditions.

Does medical cannabis work to treat chronic pain?

CADTH was asked to review the evidence on medical cannabis for the treatment of chronic pain. We found evidence on pain related to fibromyalgia, musculoskeletal pain, Crohn disease, and multiple sclerosis; however, the findings from this research weren’t clear, so we don’t know if medical cannabis can reduce pain for these patients. We did find some evidence to suggest that, for people with neuropathic pain, cannabis may have some benefit, but the benefits need to be weighed against the harms. We didn’t find any evidence for any other pain conditions. We also didn’t find any evidence on the clinical effectiveness of medical cannabis compared with other treatments for pain. As is often the case, more research is needed to know where medical cannabis fits as a treatment option for people with different types of chronic pain.

Does medical cannabis work for symptom control in palliative care patients?

There are many different reasons a patient may be receiving palliative care, but CADTH found evidence on the palliative use of medical cannabis only for patients with HIV, terminal cancer, and Alzheimer disease. There was not a lot of evidence and what we did find was of low or very low quality. Therefore, it’s uncertain what role medical cannabis may play for symptom control in palliative care patients. The low or very low-quality studies that we did find suggest that for those with HIV, medical cannabis might improve appetite and weight gain, but it also increases the risk of psychiatric side effects. For patients with cancer, dronabinol (a synthetic version of cannabis that isn’t available in Canada) might not work as well as the drug megestrol for improving appetite, weight gain, and health-related quality of life, and more people may stop taking dronabinol because of side effects. Lastly, for Alzheimer disease, dronabinol might help with weight gain and mental health symptoms. More research is needed on different palliative care populations and on medical cannabis products available in Canada, to better understand if medical cannabis has a role in palliative care in this country.

Does medical cannabis work for symptom control in patients with dementia?

The evidence suggests that medical cannabis may help treat agitation, disinhibition, aberrant behavior, nocturnal behavior disorders, as well as aberrant vocalization and resisting care in patients with dementia. It may also improve rigidity and cognitive scores. However, the available evidence is of low quality; therefore, there’s uncertainty about the role of medical cannabis for patients with dementia. More research is needed to be sure of the potential benefits and to take a closer look at the potential harms. We also need more information on dementia patients who are under age 65 and information on how medical cannabis compares with other common treatments used for this population.

Is medical cannabis safe to use with other medications?

Unfortunately, there’s not a lot of evidence to help answer this question. We found low quality evidence that oral cannabidiol (a cannabis extract not available in Canada) increases blood levels of epilepsy medications such as clobazam, eslicarbazepine, topiramate, zonisamide, and rufinamide, but we don’t know what those increased blood levels mean for patients. More research into how medical cannabis interacts with other medications will help us better understand how to use medical cannabis safely.

These are just a few of the evidence reviews CADTH has been asked to do on topics related to medical cannabis. You can find all of our related evidence at www.cadth.ca/cannabis. But CADTH is just one organization of many working to answer your questions about the medical use of cannabis. The Canadian Centre on Substance Use and Addiction (CCSA) has information on cannabis research, including the Clearing the Smoke on Cannabis series, and Health Canada has many resources on the medical use of cannabis

If you’d like to learn more about CADTH and our evidence reviews on this and other topics, please visit www.cadth.ca, follow us on Twitter at @CADTH_ACMTS, or speak to the CADTH Liaison Officer in your region.

Colleen Donder is a knowledge mobilization officer a CADTH.