- Author: Neal Handly, MD, MS, MSc; Chief Editor: Asim Tarabar, MD more...
Amphetamines are a class of compounds that are abused in many regions of the world, including the United States, Australasia, and Europe. Synthetic amphetamine compounds commonly are produced in clandestine laboratories and vary in purity and potency. Other potentials for amphetamine abuse include prescription medications often used for attention deficit disorder and various over-the-counter diet pills.
Clinical effects of amphetamine abuse are significant and commonly observed in emergency departments (EDs). The ED physician's ability to recognize and treat amphetamine intoxication is very important.
The phenylethylamine structure of amphetamines (see the image below) is similar to catecholaminergic, dopaminergic, and serotonergic agonists (biogenic amines), which may explain their actions.
The relative activities that amphetamines have to stimulate the receptors of these biogenic amines depend on the chemical substituents on the amphetamine molecule; thus, the clinical presentation depends on the type of amphetamine used. For example, methamphetamine lacks much of the peripheral stimulant properties of amphetamine while still offering euphoric and hallucinogenic properties. These actions are similar to those of cocaine; however, while effects of cocaine last for 10-20 minutes, duration of amphetamine action is much longer, lasting as long as 10-12 hours.
The routes of amphetamine administration may be oral (ingestion), inhalation (smoke), or injection (intravenous). Oral use is associated with an approximate 1-hour lag time before onset of symptoms, whereas inhaled and intravenous methods yield effects within a few minutes. Peak plasma concentrations occur in 5 minutes with intravenous use, 30 minutes with nasal or intramuscular use, and 2-3 hours postingestion.
Use appears to vary with gender and race. Research has found correlations between personality traits (risk taking and reward sensitivity) and responses to amphetamine use.
Amphetamines are a group of structurally related compounds that produce central nervous system (CNS) and peripheral nervous system (PNS) stimulation.
Central nervous system
Amphetamine compounds cause a general efflux of biogenic amines from neuronal synaptic terminals (indirect sympathomimetics). They inhibit specific transporters responsible for reuptake of biogenic amines from the synaptic nerve ending and presynaptic vesicles. Amphetamines also inhibit monoamine oxidase, which degrades biogenic amine neurotransmitters intracellularly. The net effect is an increase of neurotransmitter release into the synapse. Physiological adaptation occurs through receptor or coupling down-regulation; this tolerance and an accompanying psychological tolerance can lead to escalating use of the drug and increased toxicity. Long-term use can lead to a depletion of biogenic amine stores and a paradoxical reverse effect of the drug—a wash out.
Elevated catecholamine levels usually lead to a state of increased arousal and decreased fatigue. Increased dopamine levels at synapses in the CNS may be responsible for movement disorders , schizophrenia, and euphoria. Serotonergic signals may play a role in the hallucinogenic and anorexic aspects of these drugs.
Other serotonergic and dopaminergic effects may include resetting the thermal regulatory circuits upward in the hypothalamus and causing hyperthermia. The hyperthermia produced by amphetamines is similar to that of the serotonin syndrome.
Laboratory studies reveal that amphetamines interfere with the normal control of the neurohumoral (hypothalamopituitary) axis, affecting secretion of such factors as adrenocorticotropic hormone (ACTH). Amphetamines may alter other neural functions such as complex behavioral and learning patternings; this may be important for understanding effects of amphetamine use during pregnancy.
Animal studies indicate that amphetamines interact with N -methyl-D-aspartate (NMDA) receptors on serotonergic neurons, leading to neuronal destruction. This interaction may contribute to seizure activity.
In vitro, amphetamines have been found to stimulate regulatory molecules, such as the oncogenes c-fos and ras and cyclic adenosine monophosphate (cAMP) response element binding (CREB) protein. These proteins are responsible for signaling long-term changes at the transcriptional level.
Catecholaminergic (sympathomimetic) effects of amphetamines include inotropic and chronotropic effects on the heart, which can lead to tachycardia and other dysrhythmias. The vasoconstrictive properties of the drugs can lead to hypertension and/or coronary vasospasm.
Serotonergic action of amphetamines on peripheral vasculature can lead to vasoconstriction, which is especially problematic in placental vessels. Animal studies have shown that serotonergic actions of amphetamines effect changes in plasma levels of oxytocin, somatostatin, gastrin, and cholecystokinin.
Accurate estimation of illicit amphetamine use is difficult. An estimated 13 million Americans use these compounds without medical supervision. Random toxicologic screens performed in the ED indicate amphetamine presence in about 2% of patients.
According to National Institute on Drug Abuse estimates for 2015, 4.1% of 8th graders, 6.8% of 10th graders, and 7.7% of 12th graders had used amphetamines during the past year. Self-reporting among college students indicates an approximate 4% prevalence. An aged-matched survey of fourth-year medical students revealed that about 1.2% use amphetamines.
According to the United Nation's World Drug Report, amphetamine use worldwide declined overall from 2009 to 2013, mainly due to trends in the Americas and Europe. However, a survey of students at institutes for higher education in Belgium found no change in the pattern of amphetamine use from 2005 to 2013. Estimated worldwide prevalence of illicit use of amphetamine type stimulants in 2013 was 0.3-1.1%.
Acute overdose of amphetamines can result in the following:
Myocardial infarction 
Habitual amphetamine use produces toxic psychosis resembling paranoid schizophrenia. Hallucinations, delusions, and bizarre violent behavior are common.In a few patients, amphetamine use produces long-term paranoid schizophrenia; whether this results from unmasking underlying disease is unclear. Severe psychological depression and prolonged sleep follow chronic use and binges.
Race- and sex-related demographics
Amphetamine use characteristically occurs among single white men aged 20-35 years who are typically unemployed. Data from rural populations reveal that whites use amphetamines significantly more than African Americans. However, amphetamine use is becoming more common among women and other ethnic groups.
One study suggests that the action of estrogen within the CNS might explain why fewer women than men use amphetamines. Women in their late follicular phase (when estrogen levels are high and progesterone levels are low) were more likely to report "unpleasant stimulation" when exposed to amphetamine. This effect was not observed in the early follicular phase, when both hormone levels are low.
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