Sugar Rush. Not by itself but is converted to glucose in the body, causing a sugar rush. When added to caffeine the "energy" rush is quickly burned and then you "crash" as in all these energy drinks you see. The harm comes in the way your body "deals" with sugar and long term effects of Insulin over production and consumption. Psychological addiction is another harmful side effect. Read up on Dopamine .More.
Hypotension. Dr bell made some good points. Taurine can cause hypotension.