Cocaine occurs naturally in the leaves of the South American coca plant, although it's usually treated before it hits the streets. It comes as a white powder - cocaine hydrochloride - though people still chew the original coca leaves sometimes. Most coke users sniff it up their noses using a rolled up piece of paper, or banknote. Scientists think it works by overdosing your nerves on a natural brain messenger that tells them to feel pleasure, called dopamine. However, cocaine stops your body making dopamine after you sniff it for a while, so you can't feel happy again until you get more cocaine. Then you have to have more cocaine just to feel normal, otherwise you feel sad and irritable. The West discovered cocaine in the 1870s and thought it was fantastic. Lots of energy drinks had sprinkles of it, including Coca-Cola. It wasn't until 1900 or so that doctors realised how dangerous it is. Coca-Cola stopped using it in 1902 but kept the name.