Medical Marijuana in the Workplace: Employer Rights "Up in Smoke"?
Employers in Canada understand that they must maintain a safe work environment for their employees.
They also understand that when it comes to accommodating employees with disabilities, they must do so to the point of undue hardship. This obligation does not change if the disability involves the use of medical marijuana.
Given this fact, the approach to the use of medical marijuana in the workplace really shouldn't be any different. The accommodation process must be undertaken as if it were any other accommodation issue. But the stigma and the "politics" of marijuana can make this process confusing from an employer's perspective.
Consider updating your policies on drug|alcohol use in the workplace - marijuana is still currently illegal. Even if it becomes legalized in the near future, its use while at work will be treated just like any other drug or alcohol substance.
Employees have a responsibility to discuss their needs with the employer. Employees are part of the accommodation process! They also have a duty to participate.