I had written a loooong message which disappeared when I tried to add an image of the stuff in question. I will summarise now because I also need to get back to work or I risk being sacked... but I AM worried.
So: 21yr old DS, possibly ASD (never diagnosed) but high functioning, very turbulent as a teen, expelled from school for a few days here and there (changed schools as we searched for one that was equipped to deal with him). Depressed and medicated by age 14, he seemed to have come out of it a better adjusted. Was quite successful academically and able to go to a good uni, his first choice and Russel group. Has a long term girlfriend, and many friends with whom he seems comfortable and who seem decent people, mostly uni students but a few already working. Not so social when he's home, he spends long hours in his room on his phone or gaming, little interaction with me, DH or his siblings, joins us for meals then disappears again. I guess this is all pretty much normal behaviour for a young man his age, more or less.
But I worry about him as he's had to go through a lot and I think he gets exhausted trying to cope with our slightly chaotic home/lifestyle now he's used to having his own place. He reacts quite disproportionately when things happen without warning, his routine is disrupted etc.
Also relevant here is that we have found him lying abundantly in the past, so now I find it difficult to trust him.
However, he's been quite open about smoking weed, he knows both DH and I did at his age, so I am not judgemental but do worry about his MH, and his health in general. He tried to hide the fact he vapes, but eventually we spoke and I explained the reason why I am opposed to vaping is the lack of evidence/research/controls etc. and he knows I would really really like him to try and stop.
Now he's had a bad cough for weeks, has tested negative for COVID, and seems to not be able to shake it off. GP prescribed antibiotics and a cortisone spray but no improvement... He told me he's not smoking or vaping.
I haven't seen him showing any changes in his behaviour or appearance, no pinprick or excessively dilated pupils that might make me suspect he was high on something, but he does spend quite a bit of time "out with friends"
While he was out I went looking in his bag for any evidence of weed or vaping and instead found this little grip seal plastic bag with a chalky white powdery residue in it, didn't seem fine enough to snort (but that I wouldn't know as I haven't done it myself!). I licked a tiny bit and it was salty/unpleasant but not bitter. Had the impression that it might once have been a crushed tablet of some sort...(If you have any suggestions please enlighten me!)
And this is the question:
AIBU thinking I was justified searching his bag, given what I found, and should I talk to him about it, try to understand how heavy his use is, or should I just be ashamed for snooping/not trusting him and avoid mentioning anything openly, (also knowing that whatever I say might not have any impact on his future behaviour)
If you have made it to the end... TiA for reading and sharing your opinions.