His psychiatrist was sent his notebook. One does not see a psychiatrist unless one is on meds.
I don’t think it was “his” psychiatrist. It was a psychiatrist at the college and I don’t think Holmes had been seeing him. If he had been on meds, he would have since been going through withdrawal symptoms, and there has been no mention of that. No mention of finding any meds at his apartment, either.
That's hardly the case. Where did you come by that misapprehension of reality? Until recently, drug treatment was a rarity in psychiatry.