First of all, there are many other options to treat anxiety other than marijuana. In fact, frequent marijuana use has actually been found to cause more anxiety in certain people. In most states, marijuana is still illegal for both medical and recreational use. Not only that, but his high school probably also has a drug policy mandating consequences for using illegal drugs. It’s OK to let him know that you absolutely do not support the use of marijuana and that you will do everything in your power to make sure he refrains from using it.
This does not mean that you should not address his anxiety, however. If he is truly struggling with it, let him know that you are going to help him find other means to treat it — whether that means talking with a counselor, taking antianxiety medication or learning some coping alternatives. Think of other supportive adults who can join you when you sit him down to have this conversation. It could be an uncle, a coach, an older sibling or a friend of his who does not smoke marijuana.
As for kicking him out, most states require that a young man or woman reach the age of majority before a parent can make them leave the home. That’s 18 in most states and 19 or 21 in a few others. Rather than kick him out, think about what might motivate him to change his habit. Kids are often motivated by the notion of losing privileges if they do not comply with their parents’ rules. In today’s world, technology seems to be a big motivator to change behaviors. For instance, if he understands that smoking pot will result in his losing his smartphone or tablet or both, you may find that he suddenly loses his appetite for the drug.