Position Paper on Cannabis
This is a really interesting article, and this has always been the issue I have had with drug testing. A failed urine test doesn't necessarily show impairment it just shows the presence of the drug metabolites, so the person has used in the past. Saliva testing is a better proxy, though not the best, but probably the best option we have.
I think a lot of organisations will closely follow the police road side testing and see what approach they take and go from there.
It's important that organisations realise they're not their to moralise what their staff do outside of work as long as it isn't affecting their work. An impairment approach is an important way of doing this, it also captures other sources of impairment (fatigue, mental health etc)