This will help in stabilizing the illness. These substances may interfere with the effectiveness of medications. Be open and direct with the person when talking about the illness or treatment. Don't keep secrets. Be a good listener.
Open communication is good for everyone.
Do not be frightened by or hide the fact that a someone you care for is mentally ill. Be clear and firm that lying and violence are not 0 acceptable ways to get needs met. Treat the person as an adult. Realize that criticism usually makes things more difficult. Remember that everyone makes mistakes.