Stimulant

Stimulants, sometimes called psychostimulants or uppers, are a group of psychoactive drugs that boost alertness. They are taken to improve focus, drive, thinking, mood, and physical energy. Some occur naturally, while others are made in a lab. Common examples include caffeine, nicotine, cocaine, amphetamine, methamphetamine, methylphenidate, and modafinil. These substances ramp up activity in the sympathetic nervous system and often raise levels of excitatory neurotransmitters like norepinephrine and dopamine in the brain.

The term "stimulant" covers many drugs that increase central nervous system and body activity, produce invigorating or pleasurable effects, or have sympathomimetic actions—meaning they mimic the body's natural fight-or-flight response. The sympathetic nervous system prepares the body for action by raising heart rate, blood pressure, and breathing. Stimulants can activate the same receptors as natural chemicals like epinephrine and norepinephrine, causing similar effects.

A subset called psychostimulants act specifically at the dopamine transporter (DAT), a protein that normally removes dopamine from the space between neurons. Amphetamine, methylphenidate, cocaine, and modafinil are psychostimulants. They either block dopamine reuptake or trigger reverse transport, causing dopamine to be released. This indirect dopamine activation sets them apart from other stimulants, like caffeine, which promotes wakefulness mainly by blocking adenosine receptors.

At low doses—such as those prescribed for ADHD—stimulants can sharpen focus, boost energy, sociability, wakefulness, and libido, and may lift mood or produce euphoria. At higher doses, however, they can actually impair focus, following the Yerkes-Dodson law. Many stimulants have ergogenic effects, improving physical performance; ephedrine, pseudoephedrine, amphetamine, and methylphenidate are well-documented examples, while cocaine does the opposite. Some studies suggest that stimulants like modafinil, amphetamine, and methylphenidate may enhance cognitive function in healthy adolescents, which is a common reason for illicit use among college students. But these findings are inconclusive due to population diversity, task variability, and a lack of replication. Research on modafinil in non-sleep-deprived individuals shows mixed results—some find modest gains in attention and executive function, while others see no benefit or even a decline.

Stimulant use can also trigger psychiatric issues like psychosis, paranoia, and suicidal thoughts. Acute toxicity may cause heavy sweating, panic attacks, severe anxiety, dilated pupils, paranoia, aggression, psychosis, muscle breakdown, and repetitive, compulsive behaviors. The violent and aggressive behavior linked to acute toxicity may stem partly from paranoia. Most stimulants are sympathomimetic, so they stimulate the autonomic nervous system's sympathetic branch, leading to dilated pupils, increased heart rate, blood pressure, breathing rate, and body temperature. When these changes become pathological, they can cause arrhythmia, hypertension, and hyperthermia, potentially leading to muscle breakdown, stroke, cardiac arrest, or seizures. However, the mechanisms behind these fatal outcomes are complex and not fully understood.

Some stimulants are regulated or banned because of serious side effects, including addiction, tolerance, withdrawal, psychosis, anxiety, insomnia, cardiovascular disease, and neurotoxicity. Misuse can lead to overdose, dependence, crime, and violent behavior. Stimulants have a long history of both medical and non-medical use. Archaeological evidence from Peru shows cocaine use as early as 8000 B.C.E. They have been used to treat narcolepsy, ADHD, obesity, depression, and fatigue, and also as recreational drugs, performance enhancers, cognitive boosters, and even to promote aggression in combatants during wartime.