Everything You Need To Know About Medical Cannabis

Recreational cannabis will be legal in Canada on Oct. 17, but using it for medical purposes got the green light around 2001. Here, Dr. Danielle Martin addresses some of the big questions around medical cannabis (until now, more commonly referred to as medical marijuana), including the difference between it and recreational weed, and the conditions it's known to help.

What is medical cannabis?

Medical cannabis refers to the cannabis plant, which has two active ingredients: THC (tetrahydrocannabinol) and cannabidiol.

What's the difference between medical cannabis and recreational cannabis?

Generally, there are strict guidelines around the production of medical cannabis in Canada and it has been formulated to offer some form of relief for symptoms associated with a particular illness, or to counteract the side effects of other medical therapies. By contrast, the recreational use of cannabis triggers feelings of intoxication or alterations in mood.

Sometimes this distinction gets muddied if people use cannabis purchased for recreational use for what they perceive to be medical reasons, or if medical cannabis is used by people more interested in being intoxicated. But the purpose of the two products is quite different.

Where is the research at in terms of supporting the use of medical cannabis?

The evidence on the medical use of cannabinoids, or chemical compounds found in the cannabis plant, is still considered “sparse” when it comes to treating a host of medical conditions. The guidelines that doctors now use in Canada deal specifically with using cannabinoids to manage pain, nausea and vomiting, and muscle spasticity, which is where more of the research has been done. At the moment, there is not a lot of evidence either for or against the use of medical cannabis for most other conditions.

What are the risks of medical cannabis? 

The THC in cannabis causes alterations in mood, perceptual distortions, and cognitive impairment. Cannabis is associated with accidents, addiction to cannabis, anxiety, depression, psychosis, and poor performance at work or school. Smoking cannabis has been linked with lung and heart disease, as well as with cancer.

How can these harms be avoided?

Some people should not use medical cannabis. Young people (those who are under the age of 25) are at particularly high risk of encountering problems because their nervous systems are not yet fully developed. Individuals with a psychiatric condition (such as psychosis, depression, anxiety, or addiction) are also at high risk of encountering issues with the drug.

The harms of medical cannabis are related to the dose of THC.  We recommend a maximum daily dose of 400 mg cannabis containing 9% THC (400 mg is one small 'joint'); this was the maximum dose used in studies that looked at the use of cannabis to treat pain. The amount of cannabidiol present in the cannabis should be at least equal to and preferably greater than the amount of THC. Cannabidiol does not affect cognition or perception, and it may be responsible for the beneficial effects of cannabis.

What kind of issues is it known to help resolve?

The Canadian guidelines recommend limiting medical cannabinoid use in general, but support potential restricted use for a small subset of conditions where there is some evidence to draw from. These conditions range from neuropathic pain, palliative and end-of-life pain, chemotherapy-induced nausea and vomiting or muscle contractions from multiple sclerosis or spinal cord injury.

How is medical cannabis prescribed and should it be taken?

Currently medical cannabis in Canada is ordered by a physician and mailed to patients. Medical cannabis can be smoked, vaporized, or taken orally, mixed in food or candy (known as "edibles").  Smoking creates numerous carcinogenic chemicals and should be avoided. Edibles should be taken in very small amounts to avoid intoxication.

Guidelines warn against smoking the drug, due to the potential harms of inhalation, as well as potentially exaggerated benefits and issues around proper dosage.

Can I take medical cannabis if I am taking other medications?

There are some interactions between cannabis and anticoagulants, anti-platelet drugs or some herbs and supplements that aim to reduce blood clotting. Medical cannabis may heighten the impact of these substances, potentially increasing the risk of bleeding.

There are also possible interactions with anti-depressants, potentially increasing the sedative effect. In addition, there can be interactions with antiviral medications and other commonly used medications. Pharmacists can assist people interested in knowing whether cannabis may interact with their medications.

Is medical cannabis safe to use during pregnancy?

According to the Society of Obstetricians and Gynaecologists, cannabis could harm the growth and development of a baby if it is used during pregnancy or while a woman is breastfeeding. Guidelines also strongly recommend against the use of medical cannabinoids for things like nausea and vomiting in pregnancy, given the lack of evidence around their safety.

How long does medical cannabis last in your system?

If you have a condition for which medical cannabis is recommended under the Canadian guidelines, it is important to speak with your doctor about the appropriate dosage and how its use might affect your daily activities. In some cases, guidelines recommend against driving within 3-4 hours after inhaling around 400 mg of the drug, 6 hours if the drug was ingested by mouth, and 8 hours if a high was noted. The dosage should be reduced if sedation or intoxication occur.