A new study looked at caffeine intake and proneness to hallucinations and found a statistically significant correlation. Of course we all know that caffeine is a stimulant, but it’s not well known that it’s psychoactive. One more reason to avoid (or consume) coffee … depending on your proclivity for hallucinating.
 
Caffeine, stress, and proneness to psychosis-like experiences: A preliminary investigation. Personality and Individual Differences, In Press, Corrected Proof, Available online 19 December 2008,
Simon R. Jones and Charles Fernyhough