A neuro-stimulant was a drug administered to keep a patient from falling asleep.
Doctor Beverly Crusher injected Commander William T. Riker with a neuro-stimulant to counteract the neuro-sedative given to him by solanogen-based lifeforms whenever they abducted him into their realm. The stimulant would keep him awake when entering their realm through a spatial rupture. It was given to him before being taken for the final time by the aliens. The Doctor had to inject him with a very high dosage, as the alien sedative was very strong and warned him that the procedure might be risky. In this case the drug did work to keep him awake without any major side effects. (TNG: "Schisms")