Most amphetamine drugs sold on the street originated from the medical community.
When they're sold on the street illegally (without prescription), the name is changed,
as with the drug "speed".
Ritalin has been analyzed by independent labs and the main substances found in it are what we know of as speed and cocaine.
I don't know the medical terminology for these substances, but the medical community has a medical name for them. So if you look on a medical website you won't find the substances listed as speed or cocaine.
Drugs sold through medical outlets sometimes later on get sold on the street.
Right now Ritalin is being sold on the street illegally under different street names.
The reason for this is because people get high from it, and addicted.