I am truly sorry that your son got addicted to pain medication while serving his country.
I think Freedom1990 said it best, and that is first and foremost he has got to come to the realization that he has an addiction problem. As soon as he faces that he will then have the choice to get the help he needs.
Speaking from tons of experience with a drug addict, there is nothing you can do but support them when they are ready to seek out the help themselves. Believe me, there is tons of help out there, they just have to ask.
My son is currently in a rehab where he is being treated for dual diagnosis problems. He has been in and out of prison/jail for the past thirty years! He finally came to the conclusion that he has a problem.
You just can't do it for him. Just keep praying one day he will be ready.
Hugs, Devastated