Let's also consult Wikipedia:

Stimulants (also known as central nervous system stimulants, or psychostimulants, or colloquially as uppers) are a class of psychoactive drugs that increase alertness. They are used for various purposes, such as enhancing attention, motivation, cognition, mood, and physical performance. Some stimulants occur naturally, while others are exclusively synthetic. Common stimulants include caffeine, nicotine, cocaine (including crack cocaine), amphetamine/methamphetamine, methylphenidate, and modafinil. Most stimulants are highly addictive and damage health when addicted.