What is the law for evicting a 20 year old drug using son in New York City?

Evicting him from where ?

Does he have a rental agreement, does he have a lease, has he paid rent or is there a verbal agreement to pay rent ?

Is he using drugs in the home ?

If there is no rental agreement, he does not pay rent, and is using drugs in your home, change the locks when he is out, if there has been any agreement to a rental agreement, you will have to follow the rules for eviction of your state, including notice and eviction hearing.