The stimulant that is also referred to as crystal or crank and leaves the user feeling confused, shaky, and paranoid when it wears off is known as methamphetamine, or meth, for short. You may know about crystal meth if you ever watched the show Breaking Bad - the effects of using that drug can be seen there. Amphetamine is used for treating ADHD, narcolepsy, and obesity. Cocaine, or coke, is a recreational drug.