Cannabis prescription policies need a dose of reality


By Ian Burron

Business Edge News Magazine


The practice of providing marijuana for medicinal purposes creates major challenges for employers. 


Employers have a duty to accommodate the user of prescription marijuana up to the point of undue hardship. In this context, management needs to set policy related to the use of prescription marijuana in the workplace.


The concern for employers is, of course, related to the possibility of employee impairment. Scientific evidence indicates that marijuana can negatively affect reaction time, judgement and co-ordination.


So it seems worth considering how likely it is that an individual who is prescribed cannabis would be impaired by its regular use.


According to Health Canada, the average amount of dried marijuana prescribed is 2.1 grams per day. Health Canada also tells us that current evidence suggests that the minimum dose of THC (tetrahydrocannabinol, one of the active components of marijuana) required for therapeutic benefit without also causing a psychotropic effect is 2.5 to 3 mg. It is the THC component of cannabis that is responsible for the psychotropic effect users feel when “getting high”. It is also one of the components proposed to have therapeutic benefit.


The ideal dose of any drug is the dose that provides therapeutic benefit without causing side effect, which in the case of THC, is primarily its psychotropic effect.


Considering that the intent of prescribing cannabis is to provide therapeutic benefit rather than psychotropic affect, 2.5 to 3 mg of THC is the ideal medical dose.


Used four to five times daily at a dose of 2.5 to 3 mg, an individual would derive therapeutic benefit from 10 to 15 mg of THC per day. Yet the evidence supports that we are prescribing significantly more then that.


In fact, according to Health Canada, we are prescribing it in doses up to 20 times the appropriate amount.


The average amount of THC in prescribed marijuana is 10-15% by weight. This equates to 210-300 mg for every 2.1 grams prescribed for daily use. So if 10-15 mg per day is the ideal dose of THC, but we are prescribing 210-300 mg per day, one can easily see that we are prescribing excessively.


For context, on the basis of volume, this would be similar to prescribing 160 tablets of extra strength Tylenol per day rather than the recommended 8.


I support the legalization of marijuana and the search for more robust evidence of its medical indications. However, based on current data, it appears that the amount we are prescribing is far greater then we should be for therapeutic benefit. This virtually guarantees workplace impairment related to its use. When considered in the context of a prescribed medication, this is exactly what we should be striving to avoid.


From the perspective of an employer creating workplace policy, our current prescribing habits and their potential for creating impairment are certainly worth considering.


Ian Burron is a practising ER physician and workplace injury/disability consultant with an interest in lifestyle, obesity and preventive medicine. Visit or send a note to with feedback on this column or to suggest other topics related to the business of medicine.