APA Dictionary of Psychology

any of a group of drugs that, at low to moderate doses, heighten wakefulness and alertness, diminish fatigue, and provoke feelings of energy and well-being. At higher doses, the more powerful stimulants can produce agitation, panicked excitement, hallucinations, and paranoia. In general, stimulants exert their effects by enhancing catecholamine neurotransmission and increasing activity in the sympathetic nervous system. Cocaine and the amphetamines are examples of stimulants thought to activate the reward system (nucleus accumbens, limbic, and frontal cortex) by potentiating dopaminergic neurotransmission. Caffeine and nicotine are CNS stimulants with different mechanisms of action at adenosine receptors and nicotinic receptors, respectively. In non-Western cultures, betel nut, coca leaves, guarana, khat, and numerous other substances are used as stimulants. Some stimulants are used clinically in mental health, and in psychiatric contexts, they are often referred to as psychostimulants. These drugs include the amphetamines and related or similarly acting compounds (e.g., methylphenidate, pemoline, modafinil), used for the treatment of attention-deficit/hyperactivity disorder, narcolepsy, depression, and brain dysfunction and as appetite suppressants. Caffeine and ephedrine are ingredients of over-the-counter “alertness” medications.