I don't know that a person can be forced into rehab due to that old adage that you can't help someone who does not want help. A family member can request involuntary commitment under the Mental Health Procedures Act for a period of time. He may be able to detox and get the mental health treatment he needs.
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It is axiomatic that "it would take the patient's cooperation, input, and desire to change for any therapy to work." Having said that, your situation seems to require initiating a 302 Civil Commitment that the addict is a danger to himself or others. Since he is not a minor, this would seem to be your only option if he does not consent to voluntarily entering into a rehab program.