Does Coffee Curb Creativity?

Maria Konnikova says yes:

[We] know that much of what we associate with creativity—whether writing a sonnet or a mathematical proof—has to do with the ability to link ideas, entities, and concepts in novel ways. This ability depends in part on the very thing that caffeine seeks to prevent: a wandering, unfocused mind.

Caffeine also interferes with sleep, another ingredient in creative thought. Then again, your increased concentration could all be in your head:

Some research has found that attributes like increased alertness and focus can be replicated by the placebo effect. In a 2011 study at the University of East London, a group of psychologists examined the effects of caffeine on problem-solving ability and emotional responses. In the double-blind study, eighty-eight habitual coffee drinkers were given cups of caffeinated and decaffeinated coffee at random. Half were told that they were receiving regular coffee, and half were informed that they were given decaf. Each participant then completed tasks that measured things like reaction time, self-control, reward motivation, and mood. In the Stroop task, which measures reaction time, improved accuracy was observed in subjects who believed they had ingested caffeinated coffee, even if they had only consumed decaf. Subjects who received caffeine and were told they were drinking decaf did not show an improved reaction time.