23 Mar 1999
ANAHEIM, CALIFORNIA--Sure, we may have a few jitters and facial tics. But fellow caffeine drinkers: Rest easy. Animal studies, presented here yesterday at a meeting of the American Chemical Society, show that the juice in java is not an addictive drug.
Found in coffee, tea, and chocolate, caffeine is the most widely used psychoactive drug in the world. Few researchers contend that the mild stimulant is as dangerous as its potent and illegal counterparts, but some behavioral scientists have argued that because users seek out caffeine repeatedly, it should be considered a drug of dependence. Other experts counter that caffeine use doesn't bear other hallmarks of dependence, such as increased usage over time and the inability of users to give it up.
To try to settle this dispute, Astrid Nehlig and her colleagues at the French National Institute for Health and Medical Research (INSERM) decided to see if caffeine triggers the same increased activity in the brain's dopamine-releasing reward centers as cocaine and other stimulants do. They injected rats with a radioactive form of glucose, followed by varying doses of caffeine, equivalent to doses received by people drinking one to 10 cups of coffee. Next they killed the animals and calculated the amount of radioactive glucose--a measure of metabolic speed, and thus activity--in several brain regions, including one known as the shell of the nucleus accumbens, which has been implicated in addiction and reward.
With all but extremely high caffeine doses--equivalent to a person drinking seven cups of coffee in one sitting--Nehlig's team found increased activity in brain regions involved in locomotion, mood, and sleep, but virtually no added activity in the nucleus accumbens shell. "I do not think caffeine shows any evidence of dependence," concludes Nehlig.
Dan Steffen, a caffeine metabolism expert at Kraft Foods in Glenview, Illinois--which manufactures some caffeine-containing products--says that if the new work holds up in humans, it should end the debate over whether people become addicted to caffeine. "It's pretty powerful in that it indicates the reward system is not being activated at levels where caffeine is normally consumed," says Steffen. What does happen, Nehlig says, is that people become regular caffeine users because of the positive reinforcement they get from feeling more alert and better able to concentrate. With that said, would you please pass the cream?
--ROBERT F. SERVICE