And you thought you hated mornings.

Many people start each day with a steaming mug of coffee to sweep away the last cobwebs of sleep. But coffee just doesn't pack a big enough punch for the male members of a remote Amazonian tribe called the Achuar Jivaro, report two ethnobotanists from Washington University in St. Louis.

Walter H. Lewis and Memory Elvin-Lewis found that Achuar Jivaro tribesmen -- who live in the Amazonian regions of Peru and Ecuador -- each morning quaff an herbal tea that contains the caffeine equivalent of five cups of coffee. But even more interestingly, the two researchers discovered that the men routinely vomit up most of the tea in order to avoid caffeine-overdose symptoms such as headache, profuse sweating and a bad case of the jitters.

The daily vomiting, or emesis, "is simply part of [an Achuar Jivaro] macho ritual, passed down through the ages," says Lewis. "The tea is so pleasing that they overindulge, vomit to rid themselves of the excess caffeine, then go about their business," he says.

The Achuar Jivaro make their jolting beverage from the leaves of a South American holly, Ilex guayusa, which contains the highest percentage of caffeine by dry weight of any plant in the world, Lewis says.

Through biochemical studies, the Washington University team determined that the holly does not contain any naturally occurring emetic, which would have explained the tribesmen's vomiting.