My state has has medical marijuana coverage a while now, but employers are still allowed to screen for it and have policies against using it or being under the influence while on the job. Our job applications have a cover sheet with huge type stating you'll have to pass a drug test to get a job with us, but you wouldn't believe how many folks still try to pull the medical thing. Sorry, it's a care giving job and I just wouldn't trust someone to take care of Granny while they're stoned. I hope it never gets covered under the ADA. I do believe there is legitimate uses for it, but living in Oregon has shown me most of the card holders just want to get stoned. The medical part's a big joke here.
Are you against employing people that use other strong medicated mood altering drugs, anti psychotics, narcotics, or even drink as well? Because IMO any medication (many are labeled as such) or even legal drug can impair judgement and make for an employee risk, but that doesn't mean that all that take the drug are a risk...
I have seen my share of people on 'legit pills' taking their prescribed dosage whacked out of their noodle, I have seen my share of people that get obliterated on booze every day to the point they can't even function and pass out every night, and I have seen and I seen people smoking 'pot' with little to any noticeable 'impairment' effect... Or we could rewind that and swap any drug for the other in the previous...
I have also seen the ugly side of addiction from 'legit' strong 'pill' medications... I worked with a guy that would literally go into a trance, start jittering, sweating and start drooling (yes I'm serious) when it was time for him to take his next hand full of his 'ADA' protected prescribed pills...
IMO in the big picture marijuana taken in a prescribed dosage or off duty is one of the lesser evil drugs out there, honestly...
As always I advocate regulation and awareness, standards should be in force for many medications during employment hours and/or while doing things like driving even if they are scripted... I don't believe that if you have a script for marijuana (or any other drug) that it should be an immediate disqualification, an assessment should be make on an individual basis based on how it impacts you during the work hours...
I don't smoke but I know many that do, and probably 90% of them only do it after hours or on the weekends not during employment hours (and you might be surprised at the jobs many of them hold, from doctors, nurses, lawyers, firemen, EMTs, police, teachers and the list could go on) all would test positive if given a drug test, but are they necessary a risk at their day job because of their after hours activities? IMO the answer to that isn't a simple black and white...