Psychostimulant

Stimulants (also referred to as psychostimulants) is an overarching term that covers many drugs including those that increase activity of the body, drugs that are pleasurable and invigorating, or drugs that have sympathomimetic effects. Due to their rendering a characteristic "up" feeling, stimulants are also occasionally referred to as "uppers". Depressants or "downers", which decrease mental and/or physical function, are in stark contrast to stimulants and are considered to be the functionally opposite drug class. Stimulants are widely used throughout the world as prescription medicines as well as without a prescription (either legally or illicitly) as performance-enhancing or recreational drugs. The most frequently prescribed stimulants as of 2013 were lisdexamfetamine, methylphenidate, and amphetamine. It is estimated that the percent of the population that has abused amphetamines, cocaine and MDMA combined is between .8% and 2.1%.

Stimulants in therapeutic doses, such as those given to patients with ADHD, increases ability to focus, vigor, sociability, libido and may elevate mood. However, in higher doses stimulants may actually decrease the ability to focus, a principle of the Yerkes-Dodson Law. In higher doses stimulants may also produce euphoria, vigor, and decrease need for sleep. Many, but not all, stimulants have ergogenic effects. Drugs such as ephedrine, pseudoephedrine, amphetamine and methylphenidate have well documented ergogenic effects, while drugs such as cocaine and methamphetamine have the opposite effect. Neurocognitive enhancing effects of stimulants, specifically modafinil, amphetamine and methylphenidate have been documented in healthy adolescents, and is a commonly cited reason among illicit drug users for use, particularly among college students in the context of studying.

...
Wikipedia