I read this one at a young age, so the book dates back to the mid 60's at least. Aliens have landed and control the earth. But they become addicted to coffee and it is used by the protagonist as a lever to gain a degree of freedom, and he maybe (It's been way to long since I read it) uses it to give an overdose to one of the aliens. For some reason I'm thinking it was written by A.E. van Vogt, but nothing I can find of his matches.