Sleepiness can be described as an increased desire to sleep and a decreased propensity to stay conscious without feeling tired. It is contrasted with sedation in that it does not decrease physical energy levels but instead increases the propensity of tired, clouded, and sleep-prone behavior. This effect leads to decreased levels of motivation and drive to perform tasks due to an increase in one's desire to sleep. Prolonged exposure without appropriate rest can lead to cognitive fatigue.
Compounds within our psychoactive substance index which may cause this effect include: