Stimulants are medications that increase awareness and attention and work to fight conditions such as ADHD, narcolepsy and obesity; they are typically split into two groups, Amphetamines and, well, everything else!
"[Any] drug that excites any bodily function, but more specifically those that stimulate the brain and central nervous system. Stimulants induce alertness, elevated mood, wakefulness, increased speech and motor activity and decrease appetite. Their therapeutic use is limited, but their mood-elevating effects make some of them potent drugs of abuse." - Encyclopædia Britannica