Medical cannabis and the older adult

January 9, 2020

Contributed by:

Dr. Jim Silvius (click to view bio)

Case

Mary Brown is an 82-year-old female who comes in for routine monitoring of her heart failure and diabetes. She reports she has been having pain in her feet that interferes with her ability to sleep at night. Her granddaughter has suggested that cannabis would be an ideal treatment and she is asking for your opinion.

Issue

What is the evidence for use of cannabis and is it safe to use?

Background

Medical cannabis was first legalized in Canada in 2001 with several subsequent updates to the regulations for use. Greater interest has been seen in use of the drug since recreational cannabis was legalized in October 2018. Despite many claims for the medical benefits of cannabis, relatively little is known about the true benefit of the drug.

Cannabis sativa is the most commonly used plant for production of cannabis. More than 400 compounds are derived from the dried leaves and flowering heads. Of these, around 100 are cannabinoids with the others being non-cannabinoids. Individual plants may contain quite different amounts of specific cannabinoids related to variations in growth conditions. Of the cannabinoids, tetrahydrocannabinol (THC) is the predominantly extracted psychoactive agent, with cannabidiol (CBD) the predominantly extracted non-psychoactive agent. More than 60 different cannabinoids are also extractable with no appreciable recognized activity.

Cannabinoids act on the CB1 and/or CB2 receptors; THC is a partial agonist for both types of receptors. CBD has relatively poor affinity for the two receptor types but may act as a modulator and may potentially modulate the effect of THC when the CBD to THC ratio is >1. CB1 receptors are widely distributed throughout the body including in the CNS, heart, lung, gastrointestinal and genitourinary systems, muscle, joints, bone, and some immune sites. CB2 receptors are predominantly found in the immune system, liver, nerves and bone.

Cannabis comes in many forms including dried for smoking, solution for vaping, oils, medicinal tablets, topical preparations and edibles. There appears to be little difference in systemic blood levels from either smoking or vaping. On the other hand, because of the way they are prepared, edibles demonstrate a highly variable distribution of the active ingredients and would not be recommended for any kind of medicinal purpose. The evidence for topical preparations is essentially nonexistent with the information that is available being of very low quality and with no randomized trials to demonstrate benefit.1 The most commonly available form are the oils. Different manufacturers produce oils with different, and varying, THC and CBD concentrations. In general, oils with a higher CBD concentration are being promoted for daytime use and those with a higher THC concentration are promoted for use at night.

Many purported uses for cannabis have been suggested. In 2018, Health Canada produced an information booklet for health practitioners identifying the available information in a significant number of conditions.2 Much of the data quality was poor; however, this remains a good reference for identification of evidence that may be available for specific conditions.

In February 2018, the College of Family Physicians of Canada published an update on the prescribing of medical cannabinoids in primary care.3 This document strongly recommended against the use of cannabinoids in the majority of conditions for which they are promoted, however identified that there is limited evidence for use of a pharmaceutical form of cannabinoids in certain situations. This might include Nabilone or nabiximols depending on the situation. In none of these conditions would cannabinoids be considered first-line treatment. These conditions include refractory pain in a palliative care situation; neuropathic pain refractory to other standard therapies; refractory cancer induced nausea/vomiting; and refractory spasticity with multiple sclerosis or spinal cord injury. It is stressed that cannabinoids would be used as an adjunct only in discussion with the patient and after other evidence-informed therapies have been used without success.

The Canadian Agency for Drugs and Therapeutics and Health (CADTH) has recently completed Rapid Reviews on the use of cannabis in chronic pain4 and dementia.5 The review on the use in chronic pain revealed mixed evidence for use in neuropathic pain and for spasticity in multiple sclerosis. The review on use in dementia revealed mixed evidence for a benefit on agitation, disinhibition, irritability and vocalizations with four studies suggesting benefit in one or more of these areas and eight studies demonstrating no benefit.

Finally, a systematic review by Whiting et al identifying sleep as a secondary outcome found some benefit of nabiximols on sleep but the evidence quality was identified to be low to very low.6 This was consistent with the Health Canada review, which suggested that sleep latency and total sleep time may be improved with low-dose THC/CBD while noting that higher dose THC/CBD may cause a sleep disturbance.

Contrary to popular belief, cannabis is not without its adverse effects. These include CNS effects such as sedation, dizziness, dysphoria, etc. Cardiovascular effects include hypotension and tachycardia with potential for MI, and syncope. Respiratory effects are like those seen with tobacco smoke and GI effects include dry mouth. Drug interactions are largely unknown7 though because cannabinoids have different roles with several cytochrome P-450 enzymes, many potential drug interactions are possible.

Back to the case

How do you respond to Mary? If her foot pain is related to neuropathy, other agents may be more appropriate and/or effective in terms of management. Cannabis would not be a first-line choice. Although there is some evidence for a benefit in terms of sleep with low-dose cannabinoids, the grade of evidence is low to very low and better benefit may derive from treating the underlying issue which could be achieved with other approaches.

Bottom line

Although cannabinoids are promoted for treatment of many medical conditions, evidence of benefit is sparse and not supportive for most conditions. Where there is evidence supporting use, it is generally of low grade and recommendations for use are in refractory situations where other therapies have been tried and been unsuccessful.

References

    1. Bunka, Debbie, Marlys LeBras, and Dr. Irina Oroz. “Topical Cannabis: Does It Live Up to Its Presumed Pot Ential?” RxFiles, n.d. https://www.rxfiles.ca/RxFiles/uploads/documents/QandA-Topical Cannabis.pdf
    2. Canada, Health. “Government of Canada.” For health care professionals: Cannabis and cannabinoids - Canada.ca. Government of Canada, October 12, 2018. https://www.canada.ca/en/health-canada/services/drugs-medication/cannabis/information-medical-practitioners/information-health-care-professionals-cannabis-cannabinoids.html.
    3. “Simplified Guideline for Prescribing Medical Cannabinoids in Primary Care.” CFP - MFC - The official journal of the College of Family Physicians of Canda. Canadian Family Physician, February 2018, Vol 64. https://www.cfp.ca/content/cfp/64/2/111.full.pdf.
    4. Medical Cannabis for the Treatment of Chronic Pain: A Review of Clinical Effectiveness and Guidelines. Ottawa: CADTH; 2019 Jul. (CADTH rapid response report: summary with critical appraisal).
    5. Medical Cannabis for the Treatment of Dementia: A Review of Clinical Effectiveness and Guidelines. Ottawa: CADTH; 2019 Jul. (CADTH rapid response report: summary with critical appraisal).
    6. Whiting, Penny F., Robert F. Wolff, and Sohan Deshpande. “Cannabinoids for Medical Use.” JAMA. American Medical Association, June 23, 2015. https://jamanetwork.com/journals/jama/fullarticle/2338251.
    7. The Use of Medical Cannabis with Other Medications: A Review of Safety and Guidelines - An Update. Ottawa: CADTH; 2019 Sep. (CADTH rapid response report: summary with critical appraisal).

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