Overdosing was always a problem, and his body would go through the worst of symptoms. The phrase that he 'was a user, not an addict' made those who knew him feel sick, especially when they were aware of his habits. Now, he is set in a new situation, a flatmate who is an ex Army doctor. One of his areas of 'expertise' as Sherlock would have called it, was overdose. Perhaps it wasn't just a friend that brought them together, but necessity. (I do not own the characters or the photo that I am using for the story, this is simply a mixture of canon, headcanon, and heartcanon. Enjoy!)