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Medical Treatment of ADHD, Part 3

pillsOut of the three most commonly used medications for ADHD, Ritalin, or methylphenidate (MPH), is prescribed for more than 70 percent of patients according to one public health conference:  Although in many patients the disorder may result from the lack of brain stimulation, the medical profession leans toward treating the biochemical theory of ADHD – hence, the use of medications that affect the level of dopamine in the brain.

Dopamine is the main neurotransmitter in the “pleasure center” of the brain – a network of nerve cells or neurons that motivates much of human behavior. The “pleasure center” reinforces people’s drives to eat, drink, and procreate and is responsible for addiction.  For example, when a person tastes ice cream, the sensors of the tongue signal the brain that it feels something, and a neuron fires in the taste center of the brain.  Dopamine from one neuron is released into the space between it and another neuron.  The second neuron, in turn, sends the signal to third neuron by the same process.  Through this complicated network of signaling, the brain lets the person know that an experience is pleasurable and is worth paying attention to.

Dopamine is recycled by dopamine transporters—proteins that are embedded in the membrane of the initial neuron.  When molecules of dopamine are floating around in the synapse (or gap between neurons), any that come in contact with the transporters are sucked back into the initial neuron.  A recent study (Lancet, 1999; 354:2132-2133) showed that ADHD patients have more dopamine transporters than people without the disorder.  This means that dopamine is not given enough time to reach the second neuron and instead is taken back into the first neuron’s membrane. As a result, an inadequate number of dopamine molecules reach the second neuron so it won’t send a signal.  MPH (Ritalin) is called a reuptake inhibitor.  It blocks dopamine transporters and allows dopamine to reach the second neuron and create a signal, improving children’s ability to focus.

But Ritalin is not a cure for ADHD. The medication neither corrects the disorder nor addresses the patient’s individual problems. Eighty percent of hyperactive children have ADHD features in adolescence, and up to 65 percent maintain them in adulthood.(  Medications merely control the symptoms of hyperactivity/ impulsivity and even aggression.

Side Effects

Effects associated with moderate doses of stimulants are decreased appetite and insomnia.  Negative effects on growth rate are possible, but ultimate height appears not to be affected.  Very high doses of psychostimulants, such as Ritalin, may cause central nervous system damage, cardiovascular damage, hypertension, compulsive behaviors, and, in certain vulnerable individuals, movement disorders.  A rare percentage of children and adults treated at high doses have hallucinogenic responses.  An animal study of Ritalin has produced a “weak signal” that the drug may potentially cause cancer.  Other drugs used for ADHD have their own adverse reactions: tricyclic antidepressants may induce cardiac arrhythmias, bupropion can cause seizures, and pemoline (Cylert) is associated with liver damage.

Stimulant therapy is not recommended in patients with a history of tics or Tourette’s disorder, the presence of a thought disorder, significant resistance to such medications in the patient or family, or insufficient severity of the symptoms or dysfunction.

Ritalin’s chemical properties cause the most serious concerns about its use. MPH is a schedule II narcotic that belongs in the amphetamine family of stimulants and is regulated by the Drug Enforcement Agency (DEA) as a controlled substance.  Chronic exposure to stimulants during development may change the way the brain reacts to environmental challenges, including stressful events and pharmacological agents.  Another concern is that long-term stimulant administration in children may alter the way the brain reacts to further exposure to stimulants or other drugs with potential for abuse.

A recent study showed that MPH is not a weak stimulant, as had been thought, but is a more potent transporter inhibitor than cocaine. A typical dose given to children (0.5mg/kg) blocked 70 percent of dopamine transporters, while cocaine blocks only 50 percent. People who took MPH displayed high levels of extracellular dopamine—just as people using cocaine did.  The only difference between the MPH and the cocaine effect on the brain is in the way it is administered: MPH taken orally raises dopamine in about an hour, whereas inhaled or injected cocaine hits the brain in seconds.

In 1999, approximately 9 million Americans used prescription drugs for non-medical purposes—to get high, to have fun, to get a lift, or to calm down.  Ritalin abuse has been reported among middle and high school students. Some used it to suppress appetite or to stay awake while studying. The DEA lists Ritalin as a “drug of concern” and reports that some abusers have dissolved the tablets in water and injected the mixture, which can block small blood vessels and damage the lungs and retina of the eye.

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