My son never paid rent, is verbally abusive, drinks, uses drugs and comes in when he wants to. Do I have to begin eviction process or just change the locks?

I would say put his clothes in bags, set them on the porch and change the locks.

That is what I did to one of my sons when I was having similar problem.

Now on another, I paid for him three month rent at a flop house type rental,

But if he is not in school, and won't help with bills ( even if you don't need is abusive out they go, I am a firm beleiveer in tough love.

Yes - change the locks. He is not a guest or invitee and certainly has no rights as a tenant.

A call to the police may well be worth getting him some help.

He is at least 18, right?