Yup, that's right - tea made from the leaf of the coca plant. And you know what that's an ingredient of, don't you? Cocaine!
In fact, in Peru and Bolivia, where's it's legal to grow it, the locals use it to give them energy. It does not give any noticeable "buzz", but actually allows you to work hard for hours on end without any hunger. All the farmers and 'paysanos' chew coca leaves.
You stick a wad of leaves between your gum and cheek, throw in a bit of lye to get the reaction going, and just chew for hours. Makes your mouth go numb. Poorer people use it when they need to go to a dentist.
When the Spanish banned it, they found that all the peasant farmers, etc were A LOT less productive. So they allowed them to keep on chewing the coca leaf.
The stuff definitely has some effect. Mind you, I honestly don't know how powerful the tea made from the same stuff is. Probably a fair bit less effective.