The problem in all of this is the inherent bias that marijuana use doesn't have "levels".
Reading comments here, let's insert "glass of wine" for marijuana. What if somebody is using very small amounts for pain relief, mood elevation, relaxation? Isn't that what the glass (or two) of wine is for? Nobody gets fired for enjoying an evening drink. Even the title of this thread: "Marijuana in the workplace." Imagine a thread entitled "Wine in the workplace." The response would be "WTF are you talking about?"
The obvious bias is that any marijuana usage is treated as the equivalent of being "wasted" in alcohol terms. And that users can't control themselves on the job accordingly.
Now, parents supervising a kids sleepover should not be heavily under the influence of anything. But we'd probably not be concerned if mom and dad had that glass of wine, which in reality is more concerning than similar levels of marijuana usage.
Much the same to @rx2ski
's niece. The marijuana usage is much safer - it could have been Bacardi 151, and that can kill easily. Also kudos to your niece to feeling uncomfortable, that's exactly the response you want. My wife works in our school district, and gets to talk to counsellors and other staff who deal with these issues all the time. Two things jump out to me of their comments:
1) alcohol is dangerous messages have been somewhat effective, and has had an impact in teens using marijuana instead;
2) many kids now lack a normal fear response. This is the "Pharm Party" I mention on these threads where kids steal their parents' medications, mix them up, and then pop a grab bag because they want to "see what happens." Professionals are shocked that kids can overcome the fear of consequences since you can't manage the outcome once you swallow.
Based on this, I look to risk aversion as a parent. Marijuana is on the radar of concern, but mostly as an indicator of aspirations and focus. When an ER doc is overheard at a local hospital saying "Imagine that, another alcohol overdose from Monument" (that is, well do to white kids overdosing), that is a huge concern especially as it often also accompanies driving (I went to the funeral of a teen who died last summer in an alcohol related crash). You don't hear that about marijuana.
In that sense, a teen who tries marijuana where the parent finds out has taken the safest experimental route to a much broader life conversation. That's the good. Those girls are also potentially more isolated from the drug trade in CO. That's the better. The bad is the teen behavior that makes these years frightening.
What worries me the most, to be honest, is that girls have started acting more like boys in risk taking as part of their social mores. Since boys in particular lose all decision making competency during "hot" (as opposed to cool) emotional situations, having girls add fuel to the fire is scary. The social status drivers are why, IMO, teens are so risk adverse to things like a pharm party, and that's where the parenting is most critical.
Drugs laws are beyond the wrong message and outcomes. Making it about the workplace is about retention of bias of drug user class - we can, but you cannot. Prescriptions are fine, even on the job, and paid for by insurance, alcohol is fine off the job (and in some cases on the job with business lunches), marijuana is never fine despite significant medical benefits in many cases. What???