I bought the 45 when it first came out, but I remember thinking what an edgey song it was, similar to Yer Blues. The sleeve was clever--it was an X-ray of John's head---with his glasses on, lol.
I really like Cheap Trick's cover of it, IMO they're great with a Lennon tune.
I think John talked publicly at the time about his addiction in a great interview with Jann Wenner for Rollingstone, which was later published in paperback as Lennon Remembers. I don't have my copy anymore, but it's probably on the Internet somewhere.