Coming off H can cause death, so I caution you. You need to have him in a medically controlled detox or at least be on the phone with a nurse or medical provider of some sort who can help you.
To come off that type of addiction takes serious help. I believe he will only be successful with inpatient and I also believe you should do serious research into what facility he is sent to if any. He has to want this for him or it will be immediate relapse. Also notify the dr who was prescribing the medication so he does not do so again.
Good Luck and God Bless!