Stimulant drugs temporarily increase alertness and awareness.

They usually have increased side-effects with increased effectiveness, and the more powerful variants are therefore often prescription medicines or illegal drugs.

Cannabis, caffeine, nicotine, and cocaine are among the more familiar historical stimulants.

Humans have consumed caffeine since the Stone Age.

Early peoples found that chewing the seeds, bark, or leaves of certain plants had the effects of easing fatigue, stimulating awareness, and elevating mood.

Only much later was it found that the effect of caffeine was increased by steeping such plants in hot water.

Many cultures have legends that attribute the discovery of such plants to people living many thousands of years ago.

Stimulants, which produce a variety of different kinds of effects by enhancing the activity of the central and peripheral nervous systems, are psychoactive drugs that induce temporary improvements in either mental or physical function or both.

Caffeine, the world's most widely used psychoactive drug and by far the most common stimulant, is found in coffee, tea, and, to a lesser extent, cacao and its byproducts cocoa and chocolate.

It is included in many soft drinks, as well as a larger amount in energy drinks.

Cannabis, a genus of flowering plants that are indigenous to Central Asia, and South Asia, has a long history of use for fiber (hemp), for seed and seed oils, for medicinal purposes, and as a recreational drug.

Khat, a flowering plant native to the Horn of Africa and the Arabian Peninsula, contains the alkaloid called cathinone, an amphetamine-like stimulant, which is said to cause excitement, loss of appetite and euphoria.

Khat chewing has a long history as a social custom dating back thousands of years.

Cocaine, made from the leaves of the coca shrub, which grows in the mountain regions of South American countries such as Bolivia, Colombia, and Peru, is a stimulant but is not normally prescribed therapeutically for its stimulant properties, although it sees clinical use as a local anesthetic, particularly in ophthalmology.

Many pharmaceutical compounds are also classed as stimulants.

Modern stimulants include phenethylamines (amphetamines and methylenedioxymethamphetamine), Norepinephrine and Dopamine Reuptake Inhibitors (NDRIs), and the most recent class, Ampakines.

Stimulants are widely traded and throughout the world as prescription medicines and as illicit substances of recreational use or abuse.