A few thoughts on this contentious issue :
In every workplace where I have worked in the past 25 years, some of the brightest and best individuals in the place have been social pot smokers.
The THC from smoking a single joint is detectable up to 6 weeks after smoking it but any effect on workplace performance is not detectable after a few hours.
So blanket testing of all employees is probably counterproductive.
I reckon the time to bring out the drug test is when an employee has demonstrated the sort of incompetence that indicates that they are impaired in some way, be it through pot, speed, alchohol, whatever.
Note also that where testing is routine, the expertise at evading the testing flourishes. The word I hear is that even prison inmates find it fairly easy to pass drug tests despite using.
