Apparently, it contains the coca leaf which is used to make cocaine:

“The [Health Institute in the state of North Rhine Westphalia] examined Red Bull Cola in an elaborate chemical process and found traces of cocaine,” Bernhard Kuehnle, head of the food safety department at Germany’s federal ministry for consumer protection, told the German press on Sunday. According to this analysis, the 0.13 micrograms of cocaine per can of the drink does not pose a serious health threat — you’d have to drink 12,000 L of Red Bull Cola for negative effects to be felt — but it was enough to cause concern. Kuehnle’s agency is due to give its final verdict on Wednesday when experts publish their report.
Red Bull has always been upfront about the recipe for its new cola. Its website boasts colorful pictures of coca, cardamom and Kola nuts, along with other key “natural” ingredients. The company insists, however, that coca leaves are used as a flavoring agent only after removing the illegal cocaine alkaloid. “De-cocainized extract of coca leaf is used worldwide in foods as a natural flavoring,” said a Red Bull spokesman in response to the German government’s announcement. Though the cocaine alkaloid is one of 10 alkaloids in coca leaves and represents only 0.8% of the chemical makeup of the plant, it’s removal is mandated by international antinarcotics agencies when used outside the Andean region.

I bet this increases the sales of Red Bull here in the U.S. 🙂