While the Etiology of the ADHD remains unclear, there are many theories, which should give an answer about the causes of disease. Current generally accepted theories believe that genetic factors and the environment in which the child grows play a key role in the development of the disease. The most attention is drawn to the differences of genes, which control dopamine neurotransmission in the brain of the ADHD patients. Dopamine plays an important role in cognitive activities. Activation of dopaminergic transmission is necessary for the processes of switching attention from one stage of human cognitive activity to another. According to these theories, reduction in the concentration of dopamine in certain areas of the cerebral cortex leads to the disruption of switching attention and motivation processes in the brain. That is why kids with the ADHD seem to be active, although their activity is often erratic and unproductive and that is why stimulant drugs are used for the treatment of ADHD.
If the cause of the ADHD lies in the reduction of the dopamine concentration in the certain nerve pathways then it is needed to be elevated. For this purpose, stimulant drugs are used. Typical representatives of this group of pharmacologic agents are methylphenidate (Ritalin) and amphetamine (Adderall). The mechanism of the action of MPH (methylphenidate) is still not completely clear. Most the most widely used theory states that MPH connects to the molecules of DAT (dopamine transporter). DAT regulates the concentration of dopamine in the synapses and, therefore, its blockade increases the dopamine level in the synapses. Therapeutic doses of the Ritalin (0.3-0.6mg/kg) can cause the blockade of 50% of DAT (Engert, 2008). Researches have shown that MPH also causes the blockade of noradrenaline transporters. This lead to the elevation of the noradrenaline levels in the synapses of the brain. Mechanism of action of AMF (amphetamine) slightly differ from the action of the MPH. While it also causes blockade of DAT and noradrenaline transporters, causing the elevation of dopamine and noradrenaline levels in the synapses, AMF also directly induces the excretion of the dopamine to the synapse by the stimulation of the vesicular monoamine transporter 2 (VMAT2) in the cell. As a result, it causes greater dopamine level increase and have a stronger effect (Hodgkins, 2012).
However, the use of stimulant medications to treat ADHD caused controversies associated with side effects, unpredictable long-term supplementation consequences, as well as social and ethical questions about their use and distribution. Uncontrolled and excessive consumption of such potent drugs as methylphenidate and amphetamine can lead to the stimulant-induced psychosis and cause even productive symptoms. Uncontrolled use of the stimulants may be may be associated with their nonmedical use that can lead to addiction. In addition, the fact that the effect of psychostimulants on the brain is not studied thoroughly and negative effects may occur in the long term also causes concerns of many researchers. To dispel people’s concerns about these drugs, researchers need to conduct many studies and learn all aspects of the impact of stimulators on the human brain. However, today the fact remains that stimulants are the only group of drugs that have statistically proven effectiveness in the treatment of ADHD. For example, a study conducted in 2013 proved a short-term effect of the methylphenidate therapy in 80% of the study participants (Parker, 2013).
References:
Engert, V., & Pruessner, J. (2008). Dopaminergic and Noradrenergic Contributions to Functionality in ADHD: The Role of Methylphenidate. Current Neuropharmacology CN, 322-328.
Hodgkins, P., Shaw, M., Coghill, D., & Hechtman, L. (2012). Amfetamine and methylphenidate medications for attention-deficit/hyperactivity disorder: Complementary treatment options. European Child & Adolescent Psychiatry Eur Child Adolesc Psychiatry, 477-492.
Parker, J., Harpin, V., Wales, G., & Chalhoub, N. (n.d.). The long-term outcomes of interventions for the management of attention-deficit hyperactivity disorder in children and adolescents: A systematic review of randomized controlled trials. Psychology Research and Behavior Management PRBM, 87-87.
