Hey crackersgrampa, I see you are also from Ontario. I'm in Toronto, so if your son lives around here, he and I can toke up one day, and I'll find out if his weed is laced, or if he's just hanging around the wrong kind of crowd.

[edit] wait a second, have you ever actually seen him smoke, smelled pot smoke, or found any smoking devices that smelled like pot? If not, maybe he's just using the weed thing as a lie with a ring of truth.

It's a pretty clever trick some kids learn in their late teens; they will confess to something slightly less incriminating, to both quell your suspicion of them, as well as answer some of your questions about them. IE: A person accused of stealing $400 might fess up to taking only $20, to explain why they got so nervous when asked the question.

Maybe you asked your son if he was doing drugs, and he admitted to doing weed, because he thought it would explain his changed behaviour while hoping you would leave him alone, because it is only pot. Maybe it isn't only pot.