"The fact that I might be using medical marijuana during my FMLA time off is irrelevant. Indeed, if my condition requires me to take time off from work to use medical marijuana, that time off would also be covered by the FMLA.... What if the employer has a 'zero tolerance' drug free workplace policy? Does the employer have to take the employee back when he/she tests positive for marijuana use after an FMLA covered absence to smoke marijuana as a medical treatment?"