MamaCas,
If you have suspicions that he is using any sort of drugs then you are probably right. That's how it's been in my experience.
As for knowing if they're working on recovery, you'll just know, because you'll be able to see a distinct difference. Especially knowing your real son's characteristics and seeing different ones is a red flag. With my grown son, it's even the littlest things, like he calls me Mama normally, but calls me Mom when he's using. Never doubt your intuition and don't let anyone else make you doubt yourself.