Stimulants are prescription and illicit substances that enhance the function of the nervous system. This is the opposite effect of sedative-hypnotic drugs, like benzodiazepines, which slow down and depress the nervous system. Enhancing CNS function allows the brain to become more focused and alert.
Prescription stimulants like Adderall® and Ritalin® are given to treat ADHD and narcolepsy, while illegal stimulants like crack cocaine or crystal meth have no medical use. All of these stimulants are Schedule II controlled substances citing a high potential for abuse and addiction.