From IMDB: Sir Ian McKellen, who plays Gandalf in The Two Towers, has denied using marijuana in his “weed pipe”! The story of the Two Towers adapted from the second part of Jr Tolkein’s trilogy The Lord Of The Rings contains references to Gandalf’s enjoyment of smoking “pipe weed.” These references have often been associated with marijuana – however McKellen doesn’t believe that this holds true. He says, “There are many groups who claim the Rings as their own. Proponents of marijuana, for instance, associate pipe weed with the taste of pot. Tolkein made it very clear that it’s nicotine they’re smoking. I don’t think it was pot in their pipes. At least, there wasn’t any in mine.” [More]

[NB we’re quoting IMDB’s spelling of Tolkien’s name exactly as they write it!]