A stimulant is a general term referring to a psychoactive compound that increases alertness, wakefulness, and physiological arousal by acting upon the central nervous system. These substances primarily affect neurotransmitter levels, typically enhancing the release or blocking the reuptake of key excitatory neurotransmitters such as dopamine and norepinephrine. The pharmacological effects are diverse, ranging from mild increases in focus to significant cardiovascular stimulation. In biological and chemical contexts, stimulants are studied for their metabolic pathways and ability to cross the blood-brain barrier, making them agents of interest in research regarding mood regulation, energy metabolism, and wakefulness cycles.