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|Systematic (IUPAC) name|
|Trade names||Dexedrine, Dextrostat|
|Licence data||US Daily Med:|
|Moderate to High|
|Routes||Oral (only medically-utilized route)|
|Metabolism||CYP2D6, DBH, FMO3, XM-ligase, and ACGNAT|
|Excretion||Renal (45%); urinary pH-dependent|
|Boiling point||201.5 °C (395 °F)|
|Solubility in water||20 mg/mL (20 °C)|
|(what is this?)|
|Systematic (IUPAC) name|
|Trade names||Dexedrine, Dextrostat|
|Licence data||US Daily Med:|
|Moderate to High|
|Routes||Oral (only medically-utilized route)|
|Metabolism||CYP2D6, DBH, FMO3, XM-ligase, and ACGNAT|
|Excretion||Renal (45%); urinary pH-dependent|
|Boiling point||201.5 °C (395 °F)|
|Solubility in water||20 mg/mL (20 °C)|
|(what is this?)|
Dextroamphetamine[note 1] is a potent psychostimulant and amphetamine stereoisomer prescribed for the treatment of attention deficit hyperactivity disorder (ADHD) in children and adults and the rare sleep disorder, narcolepsy. Dextroamphetamine is also widely used by military air forces as a 'go-pill' during fatigue-inducing mission profiles such as night-time bombing missions. Preparations containing dextroamphetamine were also used in World War II as a treatment against fatigue.
The amphetamine molecule has two stereoisomers:[note 2] levoamphetamine and dextroamphetamine. Dextroamphetamine is the more active dextrorotatory, or "right-handed", enantiomer of the amphetamine molecule. Dextroamphetamine is available as a generic drug or under several brand names, including Dexedrine and Dextrostat. Dextroamphetamine is also the active metabolite of the prodrug[note 3] lisdexamfetamine.
Dextroamphetamine, like other amphetamines, elicits its stimulating effects via two distinct actions: first, it inhibits the transporter proteins for the monoamine neurotransmitters (namely the serotonin, norepinephrine and dopamine transporters) via trace amine-associated receptor 1 (TAAR1); and second, it releases these neurotransmitters from synaptic vesicles via vesicular monoamine transporter 2. It also shares many chemical and pharmacological properties with the human trace amine neurotransmiters, especially phenethylamine and N-methylphenethylamine, the latter being an isomer of amphetamine that is produced within the human body.
Dextroamphetamine is used to treat attention deficit hyperactivity disorder (ADHD) and narcolepsy, and is sometimes prescribed off-label for its past medical indications, such as depression, obesity, and nasal congestion. Long-term amphetamine exposure in some animal species is known to produce abnormal dopamine system development or nerve damage, but, in humans with ADHD, amphetamines appear to improve brain development and nerve growth. Magnetic resonance imaging (MRI) studies suggest that long-term treatment with amphetamine decreases abnormalities in brain structure and function found in subjects with ADHD, and improves function in several parts of the brain, such as the right caudate nucleus of the basal ganglia.
Reviews of clinical stimulant research have established the safety and effectiveness of long-term amphetamine use for ADHD. Controlled trials spanning two years have demonstrated treatment effectiveness and safety. One review highlighted a nine-month randomized controlled trial in children with ADHD that found an average increase of 4.5 IQ points and continued improvements in attention, disruptive behaviors, and hyperactivity.
Current models of ADHD suggest that it is associated with functional impairments in some of the brain's neurotransmitter systems; these functional impairments involve impaired dopamine neurotransmission in the mesocorticolimbic projection and norepinephrine neurotransmission in the locus coeruleus and prefrontal cortex. Psychostimulants like methylphenidate and amphetamine are effective in treating ADHD because they increase neurotransmitter activity in these systems. Approximately 70% of those who use these stimulants see improvements in ADHD symptoms. Children with ADHD who use stimulant medications generally have better relationships with peers and family members, perform better in school, are less distractible and impulsive, and have longer attention spans. The Cochrane Collaboration's review[note 4] on the treatment of adult ADHD with amphetamines stated that while amphetamines improve short-term symptoms, they have higher discontinuation rates than non-stimulant medications due to their adverse side effects.
A Cochrane Collaboration review on the treatment of ADHD in children with tic disorders such as Tourette syndrome indicated that stimulants in general do not make tics worse, but high doses of dextroamphetamine could exacerbate tics in some individuals. Other Cochrane reviews on the use of amphetamine following stroke or acute brain injury indicated that it may improve recovery, but further research is needed to confirm this.
Therapeutic doses of amphetamine improve cortical network efficiency, resulting in higher performance on working memory tests in all individuals. Amphetamine and other ADHD stimulants also improve task saliency (motivation to perform a task) and increase arousal (wakefulness), in turn promoting goal-directed behavior. Stimulants such as amphetamine can improve performance on difficult and boring tasks and are used by some students as a study and test-taking aid. Based upon studies of self-reported illicit stimulant use, students primarily use stimulants such as amphetamine for performance enhancement rather than abusing them as recreational drugs. However, high amphetamine doses that are above the therapeutic range can interfere with working memory and cognitive control.
Amphetamine is used by some athletes for its psychological and performance-enhancing effects, such as increased stamina and alertness; however, its use is prohibited at sporting events regulated by collegiate, national, and international anti-doping agencies. In healthy people at oral therapeutic doses, amphetamine has been shown to increase physical strength, acceleration, stamina, and endurance, while reducing reaction time. Amphetamine improves stamina, endurance, and reaction time primarily through reuptake inhibition and effluxion of dopamine in the central nervous system. At therapeutic doses, the adverse effects of amphetamine do not impede athletic performance; however, at much higher doses, amphetamine can induce effects that severely impair performance, such as rapid muscle breakdown and elevated body temperature.
According to the International Programme on Chemical Safety (IPCS) and United States Food and Drug Administration (USFDA),[note 5] amphetamine is contraindicated in people with a history of drug abuse, heart disease, severe agitation, or severe anxiety. It is also contraindicated in people currently experiencing arteriosclerosis (hardening of the arteries), glaucoma (an eye condition), hyperthyroidism (excessive production of thyroid hormone), or hypertension (high blood pressure). People who have experienced allergic reactions to other stimulants in the past or who are taking monoamine oxidase inhibitors (MAOIs) are advised not to take amphetamine. These agencies also state that anyone with anorexia nervosa, bipolar disorder, depression, elevated blood pressure, liver or kidney problems, mania, psychosis, Raynaud's phenomenon, seizures, thyroid problems, tics, or Tourette syndrome should monitor their symptoms while taking amphetamine. Evidence from human studies indicates that therapeutic amphetamine use does not cause developmental abnormalities in the fetus or newborns (i.e., it is not a human teratogen), but amphetamine abuse does pose risks to the fetus. Amphetamine has also been shown to pass into breast milk, so the IPCS and USFDA advise mothers to avoid breastfeeding when using it. Due to the potential for reversible growth impairments,[note 6] the USFDA advises monitoring the height and weight of children and adolescents prescribed amphetamines.
At normal therapeutic doses, the physical side effects of amphetamine vary widely by age and from person to person. Cardiovascular side effects can include cardiac dysrhythmia (irregular heart rate or rhythm; usually an increased heart rate), hypertension (high blood pressure) or hypotension (low blood pressure) from a vasovagal response, and Raynaud's phenomenon (reduced blood flow to extremities). Sexual side effects in males may include erectile dysfunction, frequent erections, or prolonged erections. Abdominal side effects may include stomach pain, loss of appetite, nausea, and weight loss. Other potential side effects include dry mouth, excessive grinding of the teeth, acne, profuse sweating, blurred vision, reduced seizure threshold, and tics (a type of movement disorder). Dangerous physical side effects are rare at typical pharmaceutical doses.
Amphetamine stimulates the medullary respiratory centers, producing faster and deeper breaths. In a normal person at therapeutic doses, this effect is usually not noticeable, but when respiration is already compromised, it may be evident. Amphetamine also induces contraction in the urinary bladder sphincter, the muscle which controls urination, which can result in difficulty urinating. This effect can be useful in treating bed wetting and loss of bladder control. The effects of amphetamine on the gastrointestinal tract are unpredictable. If intestinal activity is high, amphetamine may reduce gastrointestinal motility (the rate at which content moves through the digestive system); however, amphetamine may increase motility when the smooth muscle of the tract is relaxed. Amphetamine also has a slight analgesic effect and can enhance the pain relieving effects of opiates.
USFDA commissioned studies from 2011 indicate that in children, young adults, and adults there is no association between serious adverse cardiovascular events (sudden death, heart attack, and stroke) and the medical use of amphetamine or other ADHD stimulants.[sources 1]
Common psychological effects of therapeutic doses can include increased alertness, apprehension, concentration, decreased sense of fatigue, mood swings (elated mood followed by mildly depressed mood), increased initiative, insomnia or wakefulness, self-confidence, and sociability. Less common side effects include anxiety, change in libido, grandiosity, irritability, repetitive or obsessive behaviors, and restlessness;[sources 2] these effects depend on the user's personality and current mental state. Amphetamine psychosis (e.g., delusions and paranoia) can occur in heavy users. Although very rare, this psychosis can also occur at therapeutic doses during long-term therapy. According to the USFDA, "there is no systematic evidence" that stimulants can produce aggressive behavior or hostility.
An amphetamine overdose can lead to many different symptoms, but is rarely fatal with appropriate care. The severity of overdose symptoms vary positively with dosage and inversely with drug tolerance to amphetamine. Tolerant individuals have been known to take as much as 5 grams of amphetamine, roughly 100 times the maximum daily therapeutic dose, in a day. Symptoms of a moderate and extremely large overdose are listed below; fatal amphetamine poisoning usually also involves convulsions and coma. Chronic overdose of amphetamine poses a high risk of developing an addiction, since high doses result in increased expression of the addiction gene ΔFosB. Consistent aerobic exercise appears to magnitude-dependently reduce this risk.
|System||Minor or moderate overdose||Severe overdose[sources 3]|
|• addiction – a state characterized by compulsive engagement in rewarding behavior or compulsive drug use, despite adverse consequences|
|• reinforcing stimuli – stimuli that increase the probability of repeating behaviors paired with them|
|• rewarding stimuli – stimuli that the brain interprets as intrinsically positive or as something to be approached|
|• addictive drug – a drug that is both rewarding and reinforcing|
|• addictive behavior – a behavior that is both rewarding and reinforcing|
|• sensitization – an amplified response to a stimulus resulting from repeated exposure to it|
|• drug tolerance – the diminishing effect of a drug resulting from repeated administration at a given dose|
|• drug sensitization or reverse tolerance – the escalating effect of a drug resulting from repeated administration at a given dose|
|• drug dependence – an adaptive state associated with a withdrawal syndrome upon cessation of repeated drug intake|
|• physical dependence – dependence that involves physical–somatic withdrawal symptoms (e.g., fatigue)|
|• psychological dependence – dependence that involves emotional–motivational withdrawal symptoms (e.g., dysphoria and anhedonia)|
|(edit | history)|
Addiction is a serious risk with heavy recreational amphetamine use, but is unlikely to arise from typical medical use at therapeutic doses. Tolerance develops rapidly in amphetamine abuse, so periods of extended use require increasingly larger doses of the drug in order to achieve the same effect.
Current models of addiction from chronic drug use involve alterations in gene expression in certain parts of the brain, particularly the nucleus accumbens. The most important transcription factors[note 7] that produce these alterations are ΔFosB, cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), and nuclear factor kappa B (NFκB). ΔFosB is the most significant factor in drug addiction, since its overexpression in the nucleus accumbens is necessary and sufficient for many of the associated neural adaptations that occur; it has been implicated in addictions to alcohol, cannabinoids, cocaine, nicotine, opiates, phencyclidine, and substituted amphetamines. ΔJunD is the transcription factor which directly opposes ΔFosB. Increases in nucleus accumbens ΔJunD expression using viral vectors can reduce or, with a large increase, even block many of the neural and behavioral alterations seen in chronic drug abuse (i.e., the alterations mediated by ΔFosB). ΔFosB also plays an important role in regulating behavioral responses to natural rewards, such as palatable food, sex, and exercise. Since natural rewards induce expression of ΔFosB just like drugs of abuse do, chronic acquisition of these rewards can result in a similar pathological state of addiction. Consequently, ΔFosB is the key transcription factor involved in amphetamine addiction and amphetamine-induced sex addictions, a phenomenon known as dopamine dysregulation syndrome which has been observed in some patients taking dopaminergic medications.
The effects of amphetamine on gene regulation are both dose- and route-dependent. Most of the research on gene regulation and addiction is based upon animal studies with intravenous amphetamine administration at very high doses. The few studies that have used equivalent (weight-adjusted) human therapeutic doses and oral administration show that these changes, if they occur, are relatively minor.
A Cochrane Collaboration review on amphetamine and methamphetamine addiction and abuse indicates that the current evidence on effective treatments is extremely limited. The review indicated that fluoxetine[note 8] and imipramine[note 9] have some limited benefits in treating abuse and addiction, but concluded that there is currently no effective pharmacological treatment for amphetamine addiction or abuse. A corroborating review indicated that amphetamine addiction is mediated through increased activation of dopamine receptors and co-localized NMDA receptors in the mesolimbic dopamine pathway (a pathway in the brain that connects the ventral tegmental area to the nucleus accumbens). This review also noted that magnesium ions and serotonin inhibit NMDA receptors and that the magnesium ions do so by blocking the receptor's calcium channels. It also suggested that, based upon animal testing, pathological (addiction-inducing) amphetamine use significantly reduces the level of intracellular magnesium throughout the brain. Supplemental magnesium,[note 10] like fluoxetine treatment, has been shown to reduce amphetamine self-administration (doses given to oneself) in both humans and lab animals.
Cognitive behavioral therapy is currently the most effective clinical treatment for psychostimulant addiction. Additionally, research on the neurobiological effects of physical exercise suggests that consistent aerobic exercise, especially endurance exercise (e.g., marathon running), prevents the development of drug addiction and is an effective adjunct (supplemental) treatment for amphetamine addiction. Exercise leads to better treatment outcomes when used as an adjunct treatment, particularly for psychostimulant addictions. In particular, aerobic exercise decreases psychostimulant self-administration, reduces the reinstatement (i.e., relapse) of drug-seeking, and induces opposite effects on striatal dopamine receptor D2 (DRD2) signaling (increased DRD2 density) to those induced by pathological stimulant use (decreased DRD2 density).
According to another Cochrane Collaboration review on withdrawal in highly addicted amphetamine and methamphetamine abusers, "when chronic heavy users abruptly discontinue amphetamine use, many report a time-limited withdrawal syndrome that occurs within 24 hours of their last dose." This review noted that withdrawal symptoms in chronic, high-dose users are frequent, occurring in up to 87.6% of cases, and persist for three to four weeks with a marked "crash" phase occurring during the first week. Amphetamine withdrawal symptoms can include anxiety, drug craving, depressed mood, fatigue, increased appetite, increased movement or decreased movement, lack of motivation, sleeplessness or sleepiness, and lucid dreams. The review indicated that withdrawal symptoms are associated with the degree of dependence, suggesting that therapeutic use would result in far milder discontinuation symptoms. Manufacturer prescribing information does not indicate the presence of withdrawal symptoms following discontinuation of amphetamine use after an extended period at therapeutic doses.
Abuse of amphetamine can result in a stimulant psychosis that may present with a variety of symptoms (e.g., paranoia and delusions). A Cochrane Collaboration review on treatment for amphetamine, dextroamphetamine, and methamphetamine abuse-induced psychosis states that about 5–15% of users fail to recover completely. According to the same review, there is at least one trial that shows antipsychotic medications effectively resolve the symptoms of acute amphetamine psychosis. Psychosis very rarely arises from therapeutic use.
In rodents and primates, sufficiently high doses of amphetamine cause dopaminergic neurotoxicity, or damage to dopamine neurons, which is characterized as reduced transporter and receptor function. There is no evidence that amphetamine is directly neurotoxic in humans. High-dose amphetamine can cause indirect neurotoxicity as a result of increased oxidative stress from reactive oxygen species and autoxidation of dopamine.
Pharmacodynamics of amphetamine enantiomers in a dopamine neuron
Amphetamine and its enantiomers have been identified as potent full agonists of trace amine-associated receptor 1 (TAAR1), a GPCR, discovered in 2001, that is important for regulation of monoaminergic systems in the brain. Activation of TAAR1 increases cAMP production via adenylyl cyclase activation and inhibits the function of the dopamine transporter, norepinephrine transporter, and serotonin transporter, as well as inducing the release of these monoamine neurotransmitters (effluxion). Amphetamine enantiomers are also substrates for a specific neuronal synaptic vesicle uptake transporter called VMAT2. When amphetamine is taken up by VMAT2, the vesicle releases (effluxes) dopamine, norepinephrine, and serotonin, among other monoamines, into the cytosol in exchange.
Dextroamphetamine (the dextrorotary enantiomer) and levoamphetamine (the levorotary enantiomer) have identical pharmacodynamics, but their binding affinities to their biomolecular targets vary. Dextroamphetamine is a more potent agonist of TAAR1 than levoamphetamine. Consequently, dextroamphetamine produces roughly three to four times more central nervous system (CNS) stimulation than levoamphetamine; however, levoamphetamine has slightly greater cardiovascular and peripheral effects.
Amphetamine has a very similar structure and function to the endogenous trace amines, which are naturally occurring neurotransmitter molecules produced in the human body and brain. Among this group, the most closely related compounds are phenethylamine, the parent compound of amphetamine, and N-methylphenethylamine, an isomer of amphetamine (i.e., it has an identical molecular formula). In humans, phenethylamine is produced directly from L-phenylalanine by the aromatic amino acid decarboxylase (AADC) enzyme, which converts L-DOPA into dopamine as well. In turn, N‑methylphenethylamine is metabolized from phenethylamine by phenylethanolamine N-methyltransferase, the same enzyme that metabolizes norepinephrine into epinephrine. Like amphetamine, both phenethylamine and N‑methylphenethylamine regulate monoamine neurotransmission via TAAR1; unlike amphetamine, both of these substances are broken down by monoamine oxidase B, and therefore have a shorter half-life than amphetamine.
Amphetamine is well absorbed from the gut, and bioavailability is typically over 75% for dextroamphetamine. However, oral availability varies with gastrointestinal pH. Dextroamphetamine is a weak base with a pKa of 9–10; consequently, when the pH is basic, more of the drug is in its lipid soluble free base form, and more is absorbed through the lipid-rich cell membranes of the gut epithelium. Conversely, an acidic pH means the drug is predominantly in its water soluble cationic form, and less is absorbed.
The half-life of dextroamphetamine varies with urine pH. At normal urine pH, the half-life of dextroamphetamine is 9–11 hours. An acidic diet will reduce the half-life to 8–11 hours, while an alkaline diet will increase the range to 16–31 hours. The immediate-release and extended release variants of dextroamphetamine salts reach peak plasma concentrations at 3 hours and 7 hours post-dose respectively. Dextromphetamine is eliminated via the kidneys, with 30–40% of the drug being excreted unchanged at normal urinary pH. When the urinary pH is basic, more of the drug is in its poorly water soluble free base form, and less is excreted. When urine pH is abnormal, the urinary recovery of amphetamine may range from a low of 1% to as much as 75%, depending mostly upon whether urine is too basic or acidic, respectively. Amphetamine is usually eliminated within two days of the last oral dose. Apparent half-life and duration of effect increase with repeated use and accumulation of the drug.
CYP2D6, dopamine β-hydroxylase, flavin-containing monooxygenase, butyrate-CoA ligase, and glycine N-acyltransferase are the enzymes known to metabolize amphetamine or its metabolites in humans. Amphetamine has a variety of excreted metabolic products, including 4-hydroxyamfetamine, 4-hydroxynorephedrine, 4-hydroxyphenylacetone, benzoic acid, hippuric acid, norephedrine, and phenylacetone. Among these metabolites, the active sympathomimetics are 4‑hydroxyamphetamine, 4‑hydroxynorephedrine, and norephedrine.
Metabolic pathways of amphetamine
Racemic amphetamine was first synthesized under the chemical name "phenylisopropylamine" in Berlin, 1887 by the Romanian chemist Lazar Edeleanu. It was not widely marketed until 1932, when the pharmaceutical company Smith, Kline & French (now known as GlaxoSmithKline) introduced it in the form of the Benzedrine inhaler for use as a bronchodilator. Notably, the amphetamine contained in the Benzedrine inhaler was the liquid free-base,[note 11] not a chloride or sulfate salt.
Three years later, in 1935, the medical community became aware of the stimulant properties of amphetamine, specifically dexamfetamine, and in 1937 Smith, Kline, and French introduced tablets under the tradename Dexedrine. In the United States, Dexedrine was approved to treat narcolepsy, attention disorders, depression, and obesity. In Canada, epilepsy and parkinsonism were also approved indications. Dexamfetamine was marketed in various other forms in the following decades, primarily by Smith, Kline, and French, such as several combination medications including a mixture of dexamfetamine and amobarbital (a barbiturate) sold under the tradename Dexamyl and, in the 1950s, an extended release capsule (the "Spansule"). Preparations containing dextroamphetamine were also used in World War II as a treatment against fatigue.
It quickly became apparent that dexamfetamine and other amphetamines had a high potential for misuse, although they were not heavily controlled until 1970, when the Comprehensive Drug Abuse Prevention and Control Act was passed by the United States Congress. Dexamfetamine, along with other sympathomimetics, was eventually classified as Schedule II, the most restrictive category possible for a drug with a government-sanctioned, recognized medical use. Internationally, it has been available under the names AmfeDyn (Italy), Curban (US), Obetrol (Switzerland), Simpamina (Italy), Dexedrine/GSK (US & Canada), Dexedrine/UCB (United Kingdom), Dextropa (Portugal), and Stild (Spain).
The U.S. Air Force uses dexamfetamine as one of its "go pills", given to pilots on long missions to help them remain focused and alert. Conversely, "no-go pills" are used after the mission is completed, to combat the effects of the mission and "go-pills". The Tarnak Farm incident was linked by media reports to the use of this drug on long term fatigued pilots. The military did not accept this explanation, citing the lack of similar incidents. Newer stimulant medications or awakeness promoting agents with different side effect profiles, such as modafinil, are being investigated and sometimes issued for this reason.
In the United States, an instant-release (IR) tablet preparation of dextroamphetamine sulfate is available under the brand name Dextrostat, in 5 mg and 10 mg strengths, with generic versions marketed by Barr (Teva Pharmaceutical Industries), Mallinckrodt Pharmaceuticals and Wilshire Pharmaceuticals. Dextroamphetamine sulfate is also available as a controlled-release (CR) capsule preparation in strengths of 5 mg, 10 mg, and 15 mg under the brand name Dexedrine Spansule, with generic versions marketed by Barr and Mallinckrodt. A bubblegum flavored oral solution is available under the brand name ProCentra, manufactured by FSC Pediatrics, which is designed to be an easier method of administration in children who have difficulty swallowing tablets, each 5 mL contains 5 mg dexamfetamine.
In Australia, dexamphetamine is available in bottles of 100 instant release 5 mg tablets as a generic drug. or slow release dexamfetamine preparations may be compounded by individual chemists. Similarly, in the United Kingdom it is only available in 5 mg instant release sulfate tablets under the generic name dexamfetamine sulphate having had been available under the brand name Dexedrine prior to UCB Pharma disinvesting the product to another pharmaceutical company (Auden Mckenzie).
Dexamfetamine is the active metabolite of the prodrug lisdexamfetamine (L-lysine-dextroamphetamine), available by the brand name Vyvanse (Lisdexamfetamine dimesylate). Lisdexamfetamine is metabolised in the gastrointestinal tract, while dextroamphetamine's metabolism is hepatic. Lisdexamfetamine is therefore an inactive compound until it is converted into an active compound by the digestive system. Vyvanse is marketed as once-a-day dosing as it provides a slow release of dexamfetamine into the body. Vyvanse is available as capsules, and in six strengths; 20 mg, 30 mg, 40 mg, 50 mg, 60 mg, and 70 mg. The conversion rate of Lisdexamfetamine dimesylate to dextroamphetamine base is 0.2948, thus a 30 mg-strength Vyvanse capsule is molecularly equivalent to 8.844 mg dexamfetamine base.
Another pharmaceutical that contains dextroamphetamine is commonly known by the brand name Adderall. The drug formulation of Adderall, including both the immediate release (IR) and extended release (XR) forms, is:
Adderall is roughly three-quarters dextroamphetamine, with it accounting for 72.7% of the amphetamine base in Adderall (the remaining percentage is levoamphetamine). The salt ratio, as noted above, is 75%:25% or 3:1 dextroamphetamine to levoamphetamine.
Alternatively, direct oxidation of amphetamine by DA β-hydroxylase can afford norephedrine.
Basal ganglia regions like the right globus pallidus, the right putamen, and the nucleus caudatus are structurally affected in children with ADHD. These changes and alterations in limbic regions like ACC and amygdala are more pronounced in non-treated populations and seem to diminish over time from child to adulthood. Treatment seems to have positive effects on brain structure.
Therapeutic (relatively low) doses of psychostimulants, such as methylphenidate and amphetamine, improve performance on working memory tasks both in in normal subjects and those with ADHD. Positron emission tomography (PET) demonstrates that methylphenidate decreases regional cerebral blood flow in the doroslateral prefrontal cortex and posterior parietal cortex while improving performance of a spacial working memory task. This suggests that cortical networks that normally process spatial working memory become more efficient in response to the drug. ... [It] is now believed that dopamine and norepinephrine, but not serotonin, produce the beneficial effects of stimulants on working memory. At abused (relatively high) doses, stimulants can interfere with working memory and cognitive control ... stimulants act not only on working memory function, but also on general levels of arousal and, within the nucleus accumbens, improve the saliency of tasks. Thus, stimulants improve performance on effortful but tedious tasks ... through indirect stimulation of dopamine and norepinephrine receptors.
Dopamine acts in the nucleus accumbens to attach motivational significance to stimuli associated with reward.
Amphetamines and caffeine are stimulants that increase alertness, improve focus, decrease reaction time, and delay fatigue, allowing for an increased intensity and duration of training ...
Physiologic and performance effects
• Amphetamines increase dopamine/norepinephrine release and inhibit their reuptake, leading to central nervous system (CNS) stimulation
• Amphetamines seem to enhance athletic performance in anaerobic conditions 39 40
• Improved reaction time
• Increased muscle strength and delayed muscle fatigue
• Increased acceleration
• Increased alertness and attention to task
The neurotransmitter dopamine is released from projections originating in the midbrain. Manipulations of dopaminergic signaling profoundly influence interval timing, leading to the hypothesis that dopamine influences internal pacemaker, or “clock,” activity (Maricq and Church, 1983; Buhusi and Meck, 2005, 2009; Lake and Meck, 2013). For instance, amphetamine, which increases concentrations of dopamine at the synaptic cleft (Maricq and Church, 1983; Zetterström et al., 1983) advances the start of responding during interval timing (Taylor et al., 2007), whereas antagonists of D2 type dopamine receptors typically slow timing (Drew et al., 2003; Lake and Meck, 2013). ... Depletion of dopamine in healthy volunteers impairs timing (Coull et al., 2012), while amphetamine releases synaptic dopamine and speeds up timing (Taylor et al., 2007).
A minority of individuals who use amphetamines develop full-blown psychosis requiring care at emergency departments or psychiatric hospitals. In such cases, symptoms of amphetamine psychosis commonly include paranoid and persecutory delusions as well as auditory and visual hallucinations in the presence of extreme agitation. More common (about 18%) is for frequent amphetamine users to report psychotic symptoms that are sub-clinical and that do not require high-intensity intervention ...
About 5–15% of the users who develop an amphetamine psychosis fail to recover completely (Hofmann 1983) ...
Findings from one trial indicate use of antipsychotic medications effectively resolves symptoms of acute amphetamine psychosis.
Amphetamine, dextroamphetamine, and methylphenidate act as substrates for the cellular monoamine transporter, especially the dopamine transporter (DAT) and less so the norepinephrine (NET) and serotonin transporter. The mechanism of toxicity is primarily related to excessive extracellular dopamine, norepinephrine, and serotonin.
these data show that exercise can affect dopaminergic signaling at many different levels, which may underlie its ability to modify vulnerability during drug use initiation. Exercise also produces neuroadaptations that may influence an individual's vulnerability to initiate drug use. Consistent with this idea, chronic moderate levels of forced treadmill running blocks not only subsequent methamphetamine-induced conditioned place preference, but also stimulant-induced increases in dopamine release in the NAc (Chen et al., 2008) and striatum (Marques et al., 2008). ... [These] findings indicate the efficacy of exercise at reducing drug intake in drug-dependent individuals ... wheel running [reduces] methamphetamine self-administration under extended access conditions (Engelmann et al., 2013) ... These findings suggest that exercise may "magnitude"-dependently prevent the development of an addicted phenotype possibly by blocking/reversing behavioral and neuro-adaptive changes that develop during and following extended access to the drug. ... Exercise has been proposed as a treatment for drug addiction that may reduce drug craving and risk of relapse. Although few clinical studies have investigated the efficacy of exercise for preventing relapse, the few studies that have been conducted generally report a reduction in drug craving and better treatment outcomes (see Table 4). ... Taken together, these data suggest that the potential benefits of exercise during relapse, particularly for relapse to psychostimulants, may be mediated via chromatin remodeling and possibly lead to greater treatment outcomes.
DESPITE THE IMPORTANCE OF NUMEROUS PSYCHOSOCIAL FACTORS, AT ITS CORE, DRUG ADDICTION INVOLVES A BIOLOGICAL PROCESS: the ability of repeated exposure to a drug of abuse to induce changes in a vulnerable brain that drive the compulsive seeking and taking of drugs, and loss of control over drug use, that define a state of addiction. ... A large body of literature has demonstrated that such ΔFosB induction in D1-type NAc neurons increases an animal's sensitivity to drug as well as natural rewards and promotes drug self-administration, presumably through a process of positive reinforcement
ΔFosB has been linked directly to several addiction-related behaviors ... Importantly, genetic or viral overexpression of ΔJunD, a dominant negative mutant of JunD which antagonizes ΔFosB- and other AP-1-mediated transcriptional activity, in the NAc or OFC blocks these key effects of drug exposure14,22–24. This indicates that ΔFosB is both necessary and sufficient for many of the changes wrought in the brain by chronic drug exposure. ΔFosB is also induced in D1-type NAc MSNs by chronic consumption of several natural rewards, including sucrose, high fat food, sex, wheel running, where it promotes that consumption14,26–30. This implicates ΔFosB in the regulation of natural rewards under normal conditions and perhaps during pathological addictive-like states.
All living cells depend on the regulation of gene expression by extracellular signals for their development, homeostasis, and adaptation to the environment. Indeed, many signal transduction pathways function primarily to modify transcription factors that alter the expression of specific genes. Thus, neurotransmitters, growth factors, and drugs change patterns of gene expression in cells and in turn affect many aspects of nervous system functioning, including the formation of long-term memories. Many drugs that require prolonged administration, such as antidepressants and antipsychotics, trigger changes in gene expression that are thought to be therapeutic adaptations to the initial action of the drug.
Similar to environmental enrichment, studies have found that exercise reduces self-administration and relapse to drugs of abuse (Cosgrove et al., 2002; Zlebnik et al., 2010). There is also some evidence that these preclinical findings translate to human populations, as exercise reduces withdrawal symptoms and relapse in abstinent smokers (Daniel et al., 2006; Prochaska et al., 2008), and one drug recovery program has seen success in participants that train for and compete in a marathon as part of the program (Butler, 2005). ... In humans, the role of dopamine signaling in incentive-sensitization processes has recently been highlighted by the observation of a dopamine dysregulation syndrome in some patients taking dopaminergic drugs. This syndrome is characterized by a medication-induced increase in (or compulsive) engagement in non-drug rewards such as gambling, shopping, or sex (Evans et al., 2006; Aiken, 2007; Lader, 2008).
It has been found that deltaFosB gene in the NAc is critical for reinforcing effects of sexual reward. Pitchers and colleagues (2010) reported that sexual experience was shown to cause DeltaFosB accumulation in several limbic brain regions including the NAc, medial pre-frontal cortex, VTA, caudate, and putamen, but not the medial preoptic nucleus. ... these findings support a critical role for DeltaFosB expression in the NAc in the reinforcing effects of sexual behavior and sexual experience-induced facilitation of sexual performance. ... both drug addiction and sexual addiction represent pathological forms of neuroplasticity along with the emergence of aberrant behaviors involving a cascade of neurochemical changes mainly in the brain's rewarding circuitry.
Drugs of abuse induce neuroplasticity in the natural reward pathway, specifically the nucleus accumbens (NAc), thereby causing development and expression of addictive behavior. ... Together, these findings demonstrate that drugs of abuse and natural reward behaviors act on common molecular and cellular mechanisms of plasticity that control vulnerability to drug addiction, and that this increased vulnerability is mediated by ΔFosB and its downstream transcriptional targets. ... Sexual behavior is highly rewarding (Tenk et al., 2009), and sexual experience causes sensitized drug-related behaviors, including cross-sensitization to amphetamine (Amph)-induced locomotor activity (Bradley and Meisel, 2001; Pitchers et al., 2010a) and enhanced Amph reward (Pitchers et al., 2010a). Moreover, sexual experience induces neural plasticity in the NAc similar to that induced by psychostimulant exposure, including increased dendritic spine density (Meisel and Mullins, 2006; Pitchers et al., 2010a), altered glutamate receptor trafficking, and decreased synaptic strength in prefrontal cortex-responding NAc shell neurons (Pitchers et al., 2012). Finally, periods of abstinence from sexual experience were found to be critical for enhanced Amph reward, NAc spinogenesis (Pitchers et al., 2010a), and glutamate receptor trafficking (Pitchers et al., 2012). These findings suggest that natural and drug reward experiences share common mechanisms of neural plasticity
Although there are a variety of amphetamines and amphetamine derivatives, the word "amphetamines" in this review stands for amphetamine, dextroamphetamine and methamphetamine only.
Currently, cognitive–behavioral therapies are the most successful treatment available for preventing the relapse of psychostimulant use.
The prevalence of this withdrawal syndrome is extremely common (Cantwell 1998; Gossop 1982) with 87.6% of 647 individuals with amphetamine dependence reporting six or more signs of amphetamine withdrawal listed in the DSM when the drug is not available (Schuckit 1999) ... The severity of withdrawal symptoms is greater in amphetamine dependent individuals who are older and who have more extensive amphetamine use disorders (McGregor 2005). Withdrawal symptoms typically present within 24 hours of the last use of amphetamine, with a withdrawal syndrome involving two general phases that can last 3 weeks or more. The first phase of this syndrome is the initial "crash" that resolves within about a week (Gossop 1982;McGregor 2005) ...
Direct toxic damage to vessels seems unlikely because of the dilution that occurs before the drug reaches the cerebral circulation.
Unlike cocaine and amphetamine, methamphetamine is directly toxic to midbrain dopamine neurons.
Fig. 2. Synthetic and metabolic pathways for endogenous and exogenously administered trace amines and sympathomimetic amines ...
Trace amines are metabolized in the mammalian body via monoamine oxidase (MAO; EC 126.96.36.199) (Berry, 2004) (Fig. 2) ... It deaminates primary and secondary amines that are free in the neuronal cytoplasm but not those bound in storage vesicles of the sympathetic neurone ...
Thus, MAO inhibitors potentiate the peripheral effects of indirectly acting sympathomimetic amines ... this potentiation occurs irrespective of whether the amine is a substrate for MAO. An α-methyl group on the side chain, as in amphetamine and ephedrine, renders the amine immune to deamination so that they are not metabolized in the gut. Similarly, β-PEA would not be deaminated in the gut as it is a selective substrate for MAO-B which is not found in the gut ...
Brain levels of endogenous trace amines are several hundred-fold below those for the classical neurotransmitters noradrenaline, dopamine and serotonin but their rates of synthesis are equivalent to those of noradrenaline and dopamine and they have a very rapid turnover rate (Berry, 2004). Endogenous extracellular tissue levels of trace amines measured in the brain are in the low nanomolar range. These low concentrations arise because of their very short half-life ...
In addition to the main metabolic pathway, TAs can also be converted by nonspecific N-methyltransferase (NMT)  and phenylethanolamine N-methyltransferase (PNMT)  to the corresponding secondary amines (e.g. synephrine , N-methylphenylethylamine and N-methyltyramine ), which display similar activities on TAAR1 (TA1) as their primary amine precursors.
Concentrations of (14)C-amphetamine declined less rapidly in the plasma of human subjects maintained on an alkaline diet (urinary pH > 7.5) than those on an acid diet (urinary pH < 6). Plasma half-lives of amphetamine ranged between 16-31 hr & 8-11 hr, respectively, & the excretion of (14)C in 24 hr urine was 45 & 70%.