ADHD and Stimulant Medication

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Biology 103

2005 Second Paper

On Serendip

ADHD and Stimulant Medication

Gillian Starkey

Attention-Deficit Hyperactivity Disorder -- more commonly known as ADHD -- is a disorder that afflicts an estimated 3-6% of school-age children (1). Usually arising between the ages of 3 and 5, this disorder is characterized by atypically high levels of locomotor activity and an inability to stay mentally focused on a single task for more than a few minutes. ADHD patients often act impulsively, ignoring social norms and rules and behaving in a way that is considered obnoxious, which may be socially debilitating, especially in younger children whose peers don't understand their disorder. All of the direct symptoms of ADHD are unified by one characteristic: an inability to inhibit behavior. ADHD has no effect on an individual's level of intelligence or emotional stability, however; it only disrupts the patient's ability to focus and be productive. A common misconception about ADHD is that it directly causes children to act aggressively and defiantly, but in fact, aggression and defiance are exhibited in only about 35% of people with ADHD. In some cases, the symptoms of ADHD may be extinguished during the natural course of development; in other cases, however, the symptoms often continue on into adolescence and even adulthood.

In order to be diagnosed with ADHD and medically treated by a licensed psychiatrist, a person must have exhibited the symptoms before the age of 7. In addition, the symptoms must be pervasive (evident in at least two separate settings), and must have led to some sort of academic or social difficulty. Males are diagnosed with ADHD 3-9 times as often as females, but researchers are reluctant to attribute this to males having a higher susceptibility to the disorder. Rather, this discrepancy is most likely a result of the symptoms being simply overlooked in females; especially among young children, boys with ADHD are more easily noticed because their symptoms are more flagrant (6).

Researchers insist that there are no known environmental causes of ADHD. Scientists used to think that parents could decrease the likelihood of their children developing ADHD by controlling how much TV they watched and their sugar intake. People also thought that a stressful home life or a poor school environment could cause the disorder (3). These hypotheses have been disproven as new techniques of studying ADHD have developed; it is now known that ADHD is in fact caused by chemical levels in the brain. However, there is an element of heredity; ADHD runs in families, and in recent studies of identical twins, researchers found that if one twin has the disorder, the other is almost guaranteed to have it as well (6). In addition, adopted children with ADHD are lilely to have a biological parent with the disorder; adopted children exhibit the symptoms regardless of whether their adoptive parents have the disorder. This suggests that the development of ADHD is not influenced by social factors (6). Prenatal teratogens (chemicals taken in by a mother when pregnant that are harmful to the developing fetus) have also been linked to hyperactivity and inattention symptoms, in particular those involving long-term exposure, such as alcohol and nicotine (6).

New technology has recently enabled scientists to look at the inner workings of the brain. Scientists have used PET (positron emission tomography) scans to determine that the frontal cortical regions of the brain in particular are responsible for locomotor functions, concentration, and inhibition, all of which are involved in ADHD symptoms (1). Two specific areas that is most consistently implicated as being responsible for these functions are the prefrontal cortex and the basal ganglia. Other types of brain scans have shown that ADHD patients have significantly reduced electrical and blood flow activity in these two regions. In children with ADHD in particular, there is less brain activity in the left sensorimotor area of the cortex, which (because of the physical functions affected by the frontal cortex) would result in less control over physical activity (6). This would explain why children with ADHD are especially hyperactive.

In the basal ganglia, scientists have noticed significantly increased levels of dopamine -- a neurotransmitter which influences movement, attention, and emotion -- in people who have ADHD (7). This discovery has led to the use of dextroamphetamines and methylphenidates as treatments for ADHD. Both of these types of medications are stimulants, which may seem counterintuitive, considering ADHD patients' already-hyperactive disposition. However, stimulants are the most consistently helpful form of medication for people with ADHD. Dextroamphetamines and methylphenidates moderate the noradreneric (adrenaline-producing) and dopaminergic (dopamine-producing) systems of the endocrine system, thus bringing the dopamine levels in the basal ganglia and the electrical and blood flow levels in the frontal cortex back to normal (1).

The most commonly-prescribed methylphenidate is Ritalin; each year, approximately 2 million children in the United States take Ritalin to mask their ADHD symptoms (1). Approximately 4 million children are prescribed some other type of methylphenidate medication (4). Ritalin works by blocking dopamine transporters, therefore decreasing the amount of dopamine in the basal ganglia. Because dopamine affects movement and attention, Ritalin helps to decrease hyperactivity and promote concentration and focus by giving the ADHD patient more control over these functions (2). Adderall, the most commonly-prescribed type of dextroamphetamine, has recently become much more popular, because it remains active in the body for longer than Ritalin does, and according to some patients, has less of a "drop off effect" (4).

One main problems with these types of medication is the increasing rate of recreational use. Dextroamphetamines and methylphenidates have the same stimulating effects on healthy people without ADHD as they do on ADHD patients, so when taken in heavy doses without prescription, they can have the same basic effect as cocaine or other very potent stimulants. Ritalin and Adderall are easy to obtain, given the fairly high number of school-age children that have been prescribed these medicines to treat their ADHD. Recent surveys show that about 2.5% of 8th-graders, 3.4% of 10th-graders, and 5.1% of 12th-graders have abused Ritalin (2). Another problem with the use of stimulants to treat ADHD is the emergence of psychotic symptoms in some ADHD patients. One study at a clinic in Canada involved 98 children with ADHD who had been placed on some type of stimulant drug and 94 children who had ADHD but had never taken stimulant medication. Nine percent of the children taking stimulants exhibited psychotic symptoms of some level of intensity, whereas none of the other children exhibited these psychotic symptoms at all (5). Clearly the side effects of these stimulants need to be reexamined, but for now, these problems have resulted in media coverage and lawsuits against stimulant manufacturers.


1)Brain Imaging Data of ADHD

2) NIDA InfoFacts: Methylphenidate (Ritalin)

3)What Causes AD/HD?

4)Stimulant Drugs for ADHD and ADD

5)Confirming the Hazards of Stimulant Drug Treatment

6)Berk, Laura E. Child Development. Boston: Pearson Education, Inc., 2003.

7)Myers, David G. Psychology. New York: Worth Publishers, 2001.

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