Both my GP and the psychiatric team know all about my drug use. The former even took a blood test when my arms were covered in tracks and an abscess.
With certain mental health conditions, substance abuse / 'self-medication' is a given. I'd be the only bipolar on their books without a drug or alcohol problem if I didn't have one - in fact it's part of the diagnostic criteria.
So yeah, they're interested in my drug use, but primarily as an indicator of my mood and any worrying fluctuations. The same goes for sexual behaviour, eating, physcial activity, etc. They've been particularly encouraged by the reduction in my overall drug intake.
Thank you for your unsolicited, continued and close interest in this subject.