From an article in The Guardian (july 1, 2000):
Alongside this self-perpetuating inferno of public awareness is an oral mythology that has grown up among Red Bull customers themselves. Take the ingredient taurine. "Because of its name," says Broe (from the Red Bull company), "a lot of people think it's an extract of bull's testicles, or bile from bulls' stomachs. In fact, the glucuronolactone and the taurine we use are both pharmaceutically produced. But the minute the word of mouth dies - the minute it isn't liquid Viagra or legal cocaine - the minute it doesn't contain more caffeine than 12 espressos, then it's, like, would the last person out turn off the lights. The whole essence of Red Bull marketing isn't that we tell people what it is and why they should be drinking it. It's a word-of-mouth thing, and that's the kind of marketing you can't pay for."
and from the Red Bull web site
Frequently Asked Question: What exactly is taurine?
"Taurine is a conditionally essential amino acid, which naturally occurs in the body. At times of extreme physical exertion, the body no longer produces the required amounts of taurine, and a relative deficiency results. Taurine acts as a metabolic transmitter and additionally has a detoxifying effect and strengthens cardiac contractility."
That said, the effects of a single cup of filter coffee, with a couple of spoonfuls of sugar, will provide as much stimulation as an over priced premium energy drink containing taurine.