I tried this myself with his mom and recently with a co-worker. His mom always sticks up for him, tells me she does not smell anything (I have smelled weed smells, cat urine smells) on him ever and told me to let her know if I find out what it is...she also thinks the every now and then the neighbor behind their house burns what she calls "strawberry hickory wood" (is there such a thing?)" and it bothers her sinuses really badly .....I want so badly to tell her "no hon...its your son smoking meth in your basement" and your little sitting room is just above the fumes.
The co-worker tells me.."he is well liked and I dont see a problem but will be watching and offer help if I think he needs it".
So, its probably best like everyone else here says to just put the energy on taking care of yourself. I had to learn the hard way that blood is thicker than water and my abf has pretty much convinced his family I'm crazy, that he does not use and to just ignore most things I say.