If the feds were to legalize marijuana, but did not put in protections for legitimate documented necessity from ones doctor, one could still be fired. Drinking and using tobacco is a 100% legal activity. But companies can choose to not hire and can fire due to the use, even if off company time. There are prescription drugs that can prevent someone from holding a driving, heavy equipment, or dangerous job to to possible side effects, even though it is legally prescribed. When marijuana becomes legal for use, don't think for a minute that it will not effect your job. If a legal tobacco user can be fired for off job use (some companies drug test for nicotine, and don't allow patches or gums), they can do the same for marijuana. If medical is classified as a medicine and falls under protection of Americans with Disabilities Act, one can still have issues if the job required driving, using heavy machines, or in itself is dangerous stone cold sober such as assembly line manufacturing or working around hazardous moving equipment.