Safety Concerns

Concerns About Prescribing Medical Cannabis

As a website designed for education and interaction with patients and physicians, we welcome any concerns that physicians might have regarding the prescription of medical Cannabis. We strive to use the best possible resources to help answer any questions or concerns physicians might have about the use of medical Cannabis. We welcome any comments or questions about this content, and you can always CONTACT US to inquire further.

Addiction and Abuse

A survey of Canadian doctors conducted in 2009 by Mark Ware identified the major barriers doctors considered in regard to prescribing cannabinoids and Cannabis. The highest observed concern was the potential for patients to abuse their prescription. While this concern is valid on a case-by-case basis, the instance of abuse of any prescription is on the rise in Canada. In the most extreme case, deaths due to opioid use doubled between 1991 and 2004 according to the Canadian Centre on Substance Abuse. Although this argument does not directly involve the use of Cannabis, the growing trend of prescription abuse is of great concern.

With this in mind, and the need to provide adequate care and treatment for patients, it is important to understand all of the potential safety issues that may arise from prescribing a narcotic controlled under Canada’s Narcotics Control Regulations. This topic has been examined by medical doctors and academic researchers who have observed that like any other pharmaceutical, Cannabis has the potential to be an addictive substance. However, this observation must be made with the actual incidence of addiction between more common addictive substances in sight. A study in 2005 by Gourlay et al. from the Mount Sinai Hospital in Toronto quantified the relative potential of a patient, with no previous substance dependence, to develop a dependence on various substances. The potential to develop a dependence on Cannabis was valued at 9%; the lowest value when compared to tobacco (32%), heroin (23%), cocaine (17%), and alcohol (15%).

Ultimately, the best practice for avoiding addiction or abuse of a medical Cannabis prescription is the same as with any other high risk prescription: provide adequate screening of patients to determine their potential for abuse or addiction. In addition to adequate screening, talking to patients about low THC strains for their particular condition could also help alleviate some of the concerns regarding addiction.

Side Effects

Investigation of side effects in response to medical Cannabis and pharmaceutical cannabinoids has been a top priority of Canadian research in recent years. A long-term (two years) study of a randomized 431 patients found that the most common events in the Cannabis group were mild or moderate side effects, with only 1% of events being severe. The most commonly reported side-effects were: headache, nasopharyngitis, nausea, somnolence, and dizziness. The more serious side-effects observed with regard to cannabinoids have been associated with the use of the pharmaceutical Nabilone where the incidence of ataxia, blurred vision, and sensation disturbances was around 13%.

One of the major concerns related to side effects is the method of consuming Cannabis. Smoking Cannabis represents a very high amount of risk since the smoke produced contains a high amount of carcinogens and carbon monoxide. There are multiple conflicting studies that address the effects of smoking Cannabis. Some case studies have observed a link between smoking Cannabis and carcinoma of the upper respiratory tract. Others have found no such link. What is known is a higher incidence of bronchitis symptoms in heavy Cannabis smokers (three joints per day for 25 years or more). Data on the incidence of these types of side effects in low doses or patients who are not heavy users is less available.

Drug Interactions

As with any drug, there are bound to be antagonistic or agonistic effects in a polypharmacy situation. The available data on cannabinoid interactions with other drugs has been distilled down to the metabolic pathways of the cytochrome P450 enzyme. The CYP2C and CYP3A enzymes have been shown to be involved in the metabolism of cannabinoids. As such the following drugs have been shown to have the potential for interactions: tricyclic antidepressants, sympathomeimetic agents (amphetamines), barbiturates, anticholinergic agents (antihistamines), Disulfiram, Fluoxetine, and Theophylline. The major clinical effects of these interactions have been observed as: additive hypertension, competitive inhibition of metabolism, and isolated cases (two) of reversible hypomanic reactions.

Several studies have reported no negative drug interactions, and have even observed that the use of Cannabis with other strong pharmaceuticals (NSAIDs, TCAs, gabapentinoids, dexamethasone, metoclopramide, ondansetron, bupivacaine, and opioids) allowed for a reduced need/dependency on these pharmaceuticals.

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