Caffeine breaks down in the body to paraxanthine (80 percent) and to theophylline and theobromine (16 percent). Theophylline is also present in tea, and theobromine is present in chocolate. Adenosine is a somnogen—a sleep-promoting chemical in the body. The stimulant effects of caffeine and its metabolites (theophylline and theobromine) occur because they block adenosine receptors in the brain, and this blockage promotes sleeplessness.
