Stimulants (also known as central nervous system stimulants, or psychostimulants, or colloquially as uppers) are a class of drugs that increase the activity of the brain. They are used for various purposes, such as enhancing alertnessattentionmotivationcognitionmood, and physical performance. Some of the most common stimulants are caffeinenicotineamphetaminescocainemethylphenidatemodafinil.