From: ep. 2.2
Line: SHERLOCK: I need something stronger. Seven percent stronger.
Reference: Holmes is famous for indulging in a 7% solution of cocaine whenever he is idle. It “stimulates and clarifies the mind,” according to him. Watson is ahead of his time in admonishing him against using it, as at the time of The Sign of Four (the novel wherein we learn of Holmes’ habit), cocaine was commonly found in many food and beverage products, and easily obtained over the counter to anyone, as well as touted by many medical professionals as excellent in treatment for any number of things from respiratory issues to depression. Good on Watson for being forward-thinking (and for later breaking Holmes of the habit single-handedly).
Fun Fact: the opening scene, in which Sherlock appears in the doorway of 221B Baker St covered in blood, with a harpoon in hand, is from the beginning of short story “Black Peter,” in which Holmes does the same thing John mentions he’s done in the episode: skewer a pig. In the story, Holmes has been attempting to stab a pig clean through in one stroke, as it has everything to do with a body that was found in a case he’s on.