Even if he is suicidal--which most of us here likely doubt, as it is a familiar manipulation tactic which comes partly from the self-pity common in addicts and partly from the cunning tactic of addiction to control everyone and everything--even if he IS suicidal, as a doctor you probably know you would not be able to talk him out of his mental illness.
He has a brain disease: addiction. We cannot cure nor control any of its manifestations, including self-destruction.
We are also not addictionologists. (And even an addictionologist could only offer treatment to an addicted loved one. The addictionologist could not control the choices of any addict).
You can give him the number of AA and of the nearest rehab, if it makes you feel more at peace, and you can tell him he is a very valuable human being and worthy of help.
You need only do it one time. You will have done all you can for him.
Be at peace then. God controls his destiny.