The New Scientist Breaking News provides this one: Drinking coffee makes you more open-minded:
The coffee you drink as a pick-me-up in the morning could also make you more open to persuasion, researchers say. Evidence from a new study suggests that this happens because caffeine revs up the brain, not because it generally boosts mood.
[found via Steve Barth]
One reading of the news brief suggests caffeine is a good thing in making people more open-minded. Another reading suggests that caffeine weakens people's defenses to opinion-changing arguments. It's not completely clear from the blurb - maybe that's the point. Checking Dr Pearl Martin's c.v, it appears she is very much interested in psychological effects of various chemicals.