What drugs could he be taking?

My 20 year old son has been struggling the last few years and I am trying to figure out for sure what his issues are. I have taken him to drug counseling, family counseling, life coaching and basic counseling (to see if he was depressed or something), also to the family doctor for drug testing put I wasn't privy to the results. All the counselors have told me after just a few sessions he doesn't need to be there. YET....he continues to struggle, recently I found him to be stealing money out of my room, he emptied any bottles of old meds that were in the cabinet, failed out of college and is failing a summer class he is currently taking. He does work but just around 15/20 hours a week, and when I check his bank account after he gets paid the money is gone instantly, he has to be buying drugs. I have caught him with pot but nothing else and I am not sure what other kind of drugs he could be taking. He is never angry and never argues, if anything he is very apathetic. He is home early almost every night, I have confronted him about his eyes being red but have never found him to be stumbling or slurring his speech like he has been drinking, and never smell booze on him. I have read a lot about crack and he doesn't seem to show signs of crack use. The pot use doesn't explain how fast he goes thru money or the stealing, pots just not that expensive. If he was doing coke I think he would be staying out all night instead of coming home at 9 or 10. If he was taking opiates daily I think by now I would have caught him in a stupor. I'm sure there are many drugs available I don't know about, anyone recognize any of these signs and symptoms? I have to figure out how to help him before it's to late. Of coarse he denies there's any problems, denies taking any pills out of the cabinet, but did admit to taking the money but then told me he didn't take as much as I claimed. Any ideas?

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