For some reason this song, which I've known and loved for years has been haunting me recently. I've spent some time trying to figure out the meaning. Here's my best shot: (1) Katy is heroin (or coke?) (2) Dr. Wu is the narrator's friend/dealer In the beginning of the song, the narrator is strung out, half-way crucified (a needle in one arm?), a mess. He's out of money and needs a fix. In walks Dr. Wu who shares some of his heroin with the narrator. Everythings good for a while. Then the narrator and Dr. Wu lose touch. The narrator hears that Dr. Wu is a mess. The narrator gets in touch with Dr. Wu who agrees to supply him with some heroin. When Dr. Wu shows up he is in even worse shape than the narrator imagined. The drug has taken its toll on both of them.