A small anecdote, but when I was in high school they started drug testing if you participated in or used any non-essential services, like parking or playing on a sports team or joining a club. The effect was that a lot of people that smoked cannabis switched to spice. It was also legal at the time, so it was potentially easier to get.

In my opinion, the policy bit the school in the ass because spice had a considerably stronger and more harmful effect than cannabis.