There are over 200 kinds of amphetamines, and they're all made in a laboratory. Amphetamines bought on the street are usually less than 10% amphetamine itself - the rest is stuff like caffeine, baking soda, sugar as well as de-worming powder and other yucky stuff. Amphetamine is usually sold as a white powder, in tablets or in capsules and you can sniff it, swallow it, smoke it or inject it. Most people just eat it or stir it into a hot drink. There are different sorts of speed but all of them are related to adrenaline, the natural body chemical that gives you energy. There's also a stronger, nastier sort called Methamphetamine, which often comes as crystals to be smoked ('Crystal Meth', 'Ice', 'Glass'). Hitler is said to have been injecting speed every day at the end of World War 2. The US Army fed speed to its soldiers in Vietnam. It is worth noting that both were losers!
Amphetamines were discovered by scientists looking for a cure for asthma