September 27, 1994
Media Contact:Michael Purdy
Phone: (410) 955-8725

Something about cocaine, heroin and nicotine makes people want to use them repeatedly. But caffeine? Behavioral scientists at Johns Hopkins have done what is believed to be the first study showing that healthy, moderate caffeine users will repeatedly choose capsules containing caffeine based solely on the effects of the capsules. This property, called reinforcement, is one of the hallmarks of addiction.

For six months, Roland Griffiths, Ph.D., and co-workers tested 10 moderate caffeine users (an average of two to three cups of coffee or the caffeine equivalent daily) using sets of colored capsules. One set contained a preset dose of caffeine, the other an inert powder.

Subjects were told that the purpose of the study was to test effects of drugs found in common foods; they didn't know that capsules contained either caffeine or a placebo.

"We used a simple choice procedure," says Griffiths. "For example: on Monday you give subjects red capsules, on Tuesday blue capsules; then on Wednesday, they get to choose red or blue." Although the capsule colors were changed once every two months, the caffeine dose was standard.

Based on their experiences with the capsules on days when they could not choose, the subjects picked caffeine 80 percent of the time when they could choose.

'These studies demonstrate very clearly that caffeine acts as a reinforcer in the majority of caffeine users," says Griffiths.

"Since the usual dietary caffeine intake of the subjects in the study closely approximated that of the general population, it is likely that this phenomena would occur in most people who regularly consume caffeine," he adds.

"The case for caffeine being a reinforcer is now overwhelming. In addition to recent human experimental evidence, more than 80 percent of people in this country consume caffeine regularly. In fact, caffeine is the most widely used psychotropic (mind-affecting) drug in the world, and most people use it daily in doses high enough to affect behavior."

The study appeared in a recent issue of Behavioral Pharmacology. Co-researchers were Thomas Critchfield, of Auburn University, and Suzette Evans, of the New York State Psychiatric Institute, New York, N.Y.

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