@James DeRoest
No, I don't sit monitoring...unfortunately I know from experience that a tenant doesn't have to be using drugs to bring in unauthorized occupants, or cause other types of trouble. I am there mowing lawns from time to time so I keep track of what's going on. Letting any rental property go for to long without checking up on it is a recipe for trouble.
I respect your opinion, but there is no indication that this person is a junkie from the fact that powder cocaine was found one time in the unit. OP did not mention this person causing disruptions or complaints from neighbors. OP said there has never been any other trouble with this person. My motto is don't panic until it's time to panic.
You could immediately try to evict this person based on the drugs. If the eviction fails in court then your stuck with a hostile tenant who may stop paying, or damage the unit. If the eviction works...well you have to find a new person. That new person may have small children who tear up the unit. Or bring in an unauthorized dog that causes damage. Pick your poison.