The buzz from your morning cup of coffee may not be caused by caffeine after all. According to new research, decaffeinated coffee may be just as good at raising the blood pressure, at least for drinkers not used to the black stuff.

Numerous studies have shown that too much caffeine interferes with sleep patterns, but the long term health effects of the drug are more controversial. Some scientists claim that daily caffeine stimulation increases our risk of high blood pressure and heart disease later in life.

The researchers gave triple espressos to six regular coffee drinkers and nine volunteers who never consumed food or drinks containing caffeine. On a separate occasion, the caffeine-abstainers also drank a triple decaffeinated espresso, but they were not told which was which.

To the researchers surprise, both drinks had the same effect on the non-coffee drinkers, stimulating the sympathetic nervous system and raising blood pressure

One interpretation of the result is that the subjects are reacting like Pavlov's dog and receiving a "fake" caffeine hit in anticipation of the real thing. But lead researcher Roberto Corti, a cardiologist at University Hospital in Zurich, thinks this is unlikely because the volunteers did not usually drink coffee.

"We also saw a linear trend in blood pressure. This is not typical of a placebo effect," he adds. A more likely explanation, he thinks, is that coffee components other than caffeine have a stimulating effect.