A primer for patients' use of medicinal marijuana
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* Barbara Sibbald

Health Canada has promised guidelines for physicians whose patients want to use medicinal marijuana, but in the interim, an expert researcher offers some basic advice.

Dr. Mary Lynch, a pain researcher and head of the Canadian Consortium for the Investigation of Cannabinoids in Human Therapeutics, says there is very little research to guide practice so it's best to start with the lowest dose possible, particularly for the “naïve” (first-time) user. Using the protocols she and colleagues are developing for their research on the medicinal use of smoked marijuana, she recommends that naïve users begin with 1 puff (or toke), usually before bed, to help with symptoms such as pain or spasticity and improve sleep quality. To get the most out of a dose while limiting the amount of smoke exposure, she tells patients to inhale on the pipe or joint and hold it in their lungs as long as possible.

Experienced users often know what dose is most effective, though Lynch recommends that a dose of 2 to 4 puffs per dose, 3 times per day is reasonable and, depending on response, the dose can be titrated accordingly. (Health Canada has suggested a daily maximum dose of 5 grams.)

Lynch also cautions all users about potential side-effects, particularly those related to the central nervous system and the cardiovascular system. 

The effects on the CNS include the subjective or euphoric “high” (this is what makes the drug attractive to recreational users) and may include some perceptual alterations, time distortion and intensification of experience. Some patients, particularly naïve users, may also experience anxiety. “Prior warning along with support and reassurance are often enough to assist in controlling the anxiety,” says Lynch. There may also be impaired motor coordination and reaction time, so Lynch advises her patients not to drive while under the influence. 

There is some suggestion in the literature that individuals with schizophrenia may experience an exacerbation if exposed to cannabinoids, so patients with a history of psychosis should be advised against using marijuana. Marijuana also causes a transient increase in heart rate and can cause hypotension, which may be associated with dizziness. These effects normally disappear within 30 to 40 minutes, but Lynch suggests that naïve users should smoke in a reclining position and in the presence of another person. Lynch advises against the use of marijuana for anyone with lung, cardiac conditions, uncontrolled hypertension, a past history of psychosis, panic disorder or significant anxiety. In addition, since marijuana is a CNS depressant, patients taking other agents with CNS depressant effects may find smoking marijuana produces additive side-effects.

The bottom line, says Lynch, is that patients should discuss questions with their physicians. “It's important for people to be aware of the potential side- effects and risks right up front. It is also important for patients to follow up with their physicians to let them know of therapeutic and side effects and to review further questions.” 

Prior to consulting with patients about the use of medicinal marijuana, physicians should refer to: *The Health Effects of Cannabis*, Kalant H, et al. (editors), Centre for Addiction and Mental Health, Toronto, 1999 ([www.camh.net/resources/index.html](http://www.camh.net/resources/index.html)).