Scientists Cast Doubt
On Caffeine Addiction
BBC News Health
Many people say they need a cup to function properly
Coffee is not addictive when consumed in reasonable quantities, researchers in France have found.
Most coffee drinkers say they function better after their first cup of the day.
But scientists have debated whether caffeine - the active ingredient in the drink - is addictive.
Some people fear they grow dependent on drinks containing the chemical.
The study suggests this is unlikely, although the finding runs contrary to previous research.
Chemical conference
The new research is being presented at a national meeting of the American Chemical Society, which claims to be the world's largest scientific society.
It was conducted by Dr Astrid Nehlig, research director at the Strasbourg laboratory of INSERM, the French National Health and Medical Research Institute.
She said that at doses of one to three cups of coffee a day, caffeine has no affect on the area of the brain involved with addiction, dependence and reward.
She recently completed a study with laboratory animals.
It confirmed what any coffee drinker could tell you - that caffeine consumed in moderation contributes to increased alertness and energy.
But contrary to some findings, it found coffee does not bring about dependence at those levels.
Hard drug comparison
Dr Nehlig said caffeine appears to act differently from undeniably addictive substances such as amphetamines, cocaine, morphine or nicotine.
Even at low doses, these drugs trigger activity in the shell of the nucleus accumbens - the part of the brain responsible for addiction, she said.
It would take the equivalent of about seven or more cups of caffeinated coffee consumed in rapid succession to begin to activate this portion of the brain.
Even then, she said, "activation of the circuitry of addiction and reward occurs only at high doses of caffeine, which probably induce already adverse effects".
These effects include anxiety, nervousness and depression, she said.
Dr Nehlig acknowledged that there is a "big debate" among researchers about whether caffeine is addictive.
She said one study " reported dependence over a wide dose range", from as little as one or two cups per day to as much as 25 cups.