Legal drugs
Alcohol
Antidepressants

Both can be more dangerous than pot.

Pot like every substance out there is a different experience for each person.

If he is over 18 the best thing you can do is hold him accountable for the consequences. Lectures are not going to help and may hurt by closing of lines of communication. If he lives at home, pay rent, help around the house, no smoking or drinking in the house( if he's under 21 this is illegal and can get you in trouble) f can't then needs to find someplace else to go.

Check out self help groups for you.