@Aaron_Michael Well, basically, in Doctor Who when Rose leaves the Doctor, the Doctor becomes a whinging little bitch and takes it out on his new companion Martha. An artist called Spune decided to parody this in a comic strip in which things Martha would say would prompt the Doctor to remissness about Rose. When Martha asks, "Are they selling drugs?" in one panel, the Doctor replies, "ROSE LOVED DRUGS!"
Elsewhere, in a blog of Doctor Who episode-by-episode reviews, this comic strip is posted and immediately, Rose's love of drugs became a running joke. On April 1st as an April Fools joke, one commenter posted pretending that the blog was a Harry Potter review blog, and wharped several of the running jokes about Doctor Who into Harry Potter-related terms. "Rose loved drugs" became "Ginny loved mood-enhancing potions."
And thus this picture was born, as a spoof on the original comic strip.