Introduction to Stimulants
Stimulants are psychoactive drugs which induce temporary improvements in mental and/or physical functions. Occasionally referred to as "uppers," stimulants are the functional opposites of depressants or "downers," which decrease mental and/or physical function. Stimulants are widely used throughout the world as prescription medicines and as illicit substances of recreational use or abuse.
Function of Stimulants
Stimulants increase the activity of either the central nervous system (the brain and spinal cord), the sympathetic nervous system (part of the peripheral nervous system that controls the fight or flight response), or both. Common effects, which vary depending on the substance in question, may include enhanced alertness, awareness, wakefulness, endurance, productivity, and motivation. Effects can also include an increase in arousal, locomotion, heart rate, and blood pressure, and the perception of a diminished requirement for food and sleep. Some stimulants produce a sense of euphoria, especially those which exert influence on the central nervous system.
Stimulants exert their effects through a number of different mechanisms. Some stimulants facilitate the activity of certain neurotransmitters, specifically norepinephrine and/or dopamine. Others block the action of certain receptors (such as the adenosine receptors) in a process known as receptor antagonism. Still others cause action in other receptors (such as nicotinic acetylcholine) in a process known as receptor agonism.
Use and Abuse of Stimulants
Therapeutically, stimulants are used and/or prescribed for a variety of reasons. They are used to increase or maintain alertness; to boost endurance or productivity; to counteract fatigue and lethargy throughout the day; to counteract abnormal states that diminish alertness or consciousness (such as in narcolepsy); to decrease appetite and promote weight loss; and to enhance concentration (especially for those with attentional disorders such as ADHD). Many stimulants are also capable of improving mood and relieving anxiety, and are occasionally used to treat symptoms of depression.
The euphoria produced by some stimulants leads to their recreational use, so many stimulants are either illegal or very carefully controlled in the United States. Some may be legally available only by prescription, or not at all. Addiction to some central nervous system stimulants can quickly lead to medical, psychiatric and psychosocial deterioration. Drug tolerance, dependence, sensitization, and withdrawal can occur after repeated use. Over time, stimulants can disrupt the functioning of the brain's dopamine system, dampening users' ability to feel any pleasure at all.
Types of Stimulants
Examples of well known stimulants include amphetamines, MDMA, NDRIs, cocaine, caffeine, and nicotine.
Amphetamines (such as ephedrine, amphetamine, and methamphetamine) are a group of stimulants that increase the levels of norepinephrine and dopamine in the brain through reuptake inhibition - meaning they block these neurotransmitters from being reabsorbed back into the neural networks. Amphetamines are known to cause elevated mood and euphoria, and are often used for their therapeutic effects. Physicians occasionally prescribe amphetamines to treat major depression, and numerous studies have demonstrated the effectiveness of drugs such as Adderall in controlling symptoms associated with ADHD. Due to their availability and fast-acting effects, amphetamines are prime candidates for abuse.
Methylenedioxymethamphetamine (MDMA), known by its common street name "Ecstasy," had a medical application as a treatment for depression and a psychotherapy aid until 1985, when it became a controlled substance. The stimulant effects of MDMA include appetite loss, euphoria, social disinhibition, insomnia, improved energy, increased arousal, and increased perspiration. MDMA differs from most stimulants in that its primary pharmacological effect is on the neurotransmitter serotonin rather than dopamine, epinephrine, or norepinephrine.
Norepinephrine and Dopamine Reuptake Inhibitors (NDRIs) (such as the antidepressant Wellbutrin) inhibit the uptake of dopamine and norepinephrine, effectively increasing their amounts in the brain and causing a stimulating effect. Many of these compounds are effective ADHD medications and antidepressants. These medicines have an extended release mechanism, and are typically less popular for abuse.
Cocaine is made from the leaves of the coca shrub, which grows in the mountain regions of South America. In Europe and North America, the most common form of cocaine is a white crystalline powder (Figure 1). Most cocaine use is recreational and its abuse potential is high, and so its sale and possession are strictly controlled in most jurisdictions.
Caffeine is a drug that is found naturally in coffee, tea, soft drinks, and cocoa. Caffeine stimulates the body, increases heart rate and blood pressure, and facilitates alertness and concentration. The vast majority (over 80%) of people in the United States consume caffeine on a daily basis. In very low concentrations, nicotine also acts as a stimulant, and it is one of the main factors responsible for the dependence-forming properties of tobacco smoking.