It's so hard when it's a child. But, yes, the only way to get them out is eviction. If they don't pay rent, you can get them out in 10 days. Do you think he would be willing to negotiate a contract to stay? If you do have to end up evicting, keep yourself safe... I believe he is allowed to stay in the house until the day the eviction notice says he has to be out. Make sure to put up valuables, sentimental stuff, etc (depending on your son). Hopefully he would be willing to do stuff to stay (ie rehab, etc).

Been there, am there and it does indeed suck (not so much with drug addiction as mental unwellness and unwillingness to get help). So sorry you are dealing with this. I wish you much strength.