Greg: 7% solution of cocaine; morphine.
In the Holmes stories, Sherlock used a 7% solution of cocaine, during times of boredom.
The 7% Solution was later a movie in the 1970's, that dealt with Holmes's growing addiction to cocaine, and his treatment at the hands of Sigmund Freud.
And, in one of the stories, Holmes was found, by Watson, to be in an opium den, while in disguise. Whether or not he was taking opium is up for debate.