I don't think it is your responsibility to tell the doctor, however I understand the powerful urge to do so.
Here is what I did for my father for a completely unrelated to addiction issue, however it was one my father would not speak to the dr about and I was concerned.
I called and got the fax number of the office.
I sent a fax to the doctor explaining the situation and the issue I was concerned with. I told him I understand HIPPA and that I was not asking for any info back, it was just that I knew my father would not tell him this and it is directly related to his health and his doctor needs to know.
I then faxed it over with very clear instructions to make sure it is read by the doctor and put in my father's chart. This was done.
I see the same doctor on occasion. He told me that while he cannot discuss my father's health with me, that what I did was immensely helpful in helping him effectively treat my father.
Just a thought......
Good Luck and God Bless!