A stimulant was a type of drug intended to temporary stimulate mental or physical functions. Mild stimulants, such as the caffeine found in tea and coffee, were amongst the most commonly used non-medical drugs in several species.
In 2154, when Phlox found his sleep cycle disturbed by Orion pheromones, he relied on stimulants to stay awake. (ENT: "Bound")
During the mid-2260s, an experimental chemical stimulant designed to speed up reproduction and replacement of blood in the bodies of certain species was developed that was successfully tested in Rigelian test subjects on Rigel V. (TOS: "Journey to Babel")
In 2374, Tim Watters took cordafin stimulants for two months while in command of the USS Valiant. (DS9: "Valiant")
In the same year, while the USS Voyager was traversing a Mutara class nebula featuring heavy subnucleonic radiation, the radiation had a negative impact on the ship's technology, including its computer. The Doctor, hearing the computer's slowed vocal response to a command, suggested that it might need a stimulant. (VOY: "One")