With some states legalizing some marijuana use, how can a company know what is allowed in a drug and alcohol policy?

Just because marijuana use is legalised doesn't mean you have to allow employees to work stoned.
After all do you allow drunks at work ?

So why should it make any difference to a company's policy ?

Companies have the right to decide whether drugs and alcohol can be consumed on their premisies and whether employees are at risk if they have consumed drugs or alcohol. These things come under the requirements of workplace safety and the duty of care

The drug policy should simply prohibit illegal drugs or any medication that would affect one's ability to do their job.

Companies have the right to decide whether drugs and alcohol can be consumed on their premisies and whether employees are at risk if they have consumed drugs or alcohol. These things come under the requirements of workplace safety and the duty of care

Thank you paraclete. It is hard to tell what to do with all the new rules. Do you happen to work in HR?

Alcohol is legal and its use is controlled, even prohibited for the influence during working time.

When I took prescription medication, many positions required I give the company a list of any and all. I those "legal" drugs could affect my work, I may have to stay home, till I have been clear of them.