Three new studies conducted in animals, published in the December issue of the journal Biological Psychiatry, provide evidence that misuse of the stimulant methylphenidate (Ritalin) may have long-term effects on the brain and behavior. While methylphenidate and other stimulant medications are the recommended treatments for Attention Deficit Hyperactivity Disorder (ADHD), based on the more than 150 controlled studies demonstrating their safety and efficacy when used as prescribed, these three studies showed changes in the brains of young (adolescent or pre-adolescent) animals that persisted into adulthood. In both animals and humans, the brain continues to develop throughout adolescence. If the current studies are applicable to humans, they could have important implications for young people who use stimulants for recreational purposes.
In the first study, Dr. Cindy Brandon and her colleagues at the Finch University of Health Sciences/The Chicago Medical School examined how low doses of methylphenidate affect dopamine cells in the brains of adolescent rats. Dopamine is a brain chemical that has been implicated in natural rewards, such as food and sex, as well as in drug abuse and addiction. The study showed that the rats experienced brain cell changes that subsequently made them more sensitive to the rewarding effects of cocaine.
In the second study, Dr. William Carlezon, Jr., and his colleagues at Harvard Medical School and McLean Hospital in Belmont, Massachusetts, looked at how pre-adolescent exposure to methylphenidate affected certain behaviors in rats when they reached adulthood. They found that early exposure to twice-daily injections of methylphenidate actually reduced the sensitivity to cocaine reward, but increased other behaviors that could indicate depression. The timing of exposure to methylphenidate may be important — in this study the rats were exposed at an age corresponding to childhood, whereas in the study by Dr. Brandon et al., the rats were slightly older, more akin to adolescence.
In the third study, Dr. Carlos Bolaños and his colleagues at the University of Texas Southwestern Medical Center in Dallas assessed certain behaviors of adult rats given methylphenidate prior to adolescence. They found that compared to drug-naive rats, those chronically exposed to methylphenidate were less responsive to natural rewards, such as sugar and sex, and more sensitive to stressful situations. The methylphenidate-exposed animals also had increased anxiety-like behaviors, and enhanced blood levels of stress hormones.
Adolescent exposure to Ritalin may increase sensitivity to cocaine but pre-adolescent exposure may decrease cocaine sensitivity. That a drug can have different effects depending on the age of the patient is not surprising when we consider the amount of brain growth and changing in configuration that happens during adolescence. A drug is going to have a different effect on a rapidly growing nervous system as compared to its effects on a nervous system that is growing less rapidly or which is going through different kinds of changes.
One big caveat about these studies is that children with ADD (attention deficit disorder) or ADHD (attention deficit hyperactivity disorder) may be so different cogntively than other children that the long term effects of methylphenidate on ADD/ADHD children may be substantially different than that reported for what are considered to be "normal" mice. But it is unclear whether that means methylphenidate will have worse or better effects on ADD/ADHD children. Also, the rats were given the drug intravenously whereas children usually take it as a pill which means the drug is not going to reach the brain as quickly or not necessarily even in the same chemical state.
What is amazing about this is the scale on which doctors and parents have embarked upon a massive experiment that may cause a variety of lasting changes on cognitive function. As of 1995 2.8 percent of American children were on methylphenidate (Ritalin) and that represented a sharp increase from 1.2% in 1990. Methylphenidate use is also up in Canada and some other Western countries in about the same time period.
If anyone doubts whether, when it becomes possible to do so, humans will be willing to reengineer their minds or the minds of their offspring consider the use of nervous system-altering drugs on children today. Look at how willing parents and authority figures are to embrace treatments that are not sufficiently well understood and which probably have a number of lasting effects on cognitive function thoroughout the rest of the lives of the children who are given methylphenidate and other nervous system drugs.
|Share |||Randall Parker, 2004 January 05 01:15 PM Brain Addiction|