Pre-teens who have been treated with methylphenidate may develop an aversion to abusable drugs, according to a team of researchers from Harvard Medical School. The Harvard study also rebuts arguments that treating children with stimulants such as Ritalin, Concerta or other medications containing methylphenidate may lead to later substance abuse. The results of the research were released in a special advance online publication of the Journal of Nature Neuroscience.
Susan Anderson, Ph.D., lead author of the Harvard study, notes that the relationship between ADHD medications and substance abuse has been the subject of apparently contradictory studies. "Evidence in laboratory animals indicates that exposure to stimulants produces sensitization to their rewarding effects, a process that in humans would be expected to increase the risk of substance abuse" she writes. Anderson also notes that studies by Biederman and others have shown that the proper use of stimulants in children with ADHD actually reduces their risk of substance abuse.
The Harvard study indicates that such differing conclusions may be the result in differences that occur in the brain during development, particularly during the pre-adolescent period. According to Anderson, early exposure to methylphenidate may cause lasting changes in the way the brain uses dopamine, changes that could create an aversion to the effects of cocaine. These changes only occur while the brain developing during childhood.
Rats who were initially exposed to methylphenidate as adults showed no similar changes. "These findings suggest that the neurobiological effects of MPH depend critically upon the developmental stage within which treatment first occurs," writes Anderson.
Changing the brain changes patterns of addiction
Unlike humans, rats don't have any societal pressures to use or not use drugs. Rats work for rewards. If there is no reward for a behavior, then they don't continue to exhibit the behavior.
In the Harvard study, methylphenidate appeared to decrease the rewarding effects of cocaine, thus reducing the potential for use or abuse. Medicated rats observed by Anderson also displayed less tolerance for the aversive effects of cocaine. This decreased reward combined with greater adverse reactions caused the rats to develop an aversion to cocaine.
How strong was their dislike of cocaine? These rats not only did not develop an addiction to the drug - they didn't even want to be in areas that they associated with cocaine use.
However, unmedicated rats developed the same type of addictive behaviors that one would expect when they were exposed to cocaine. The reward they received from the drug was sufficient for them to continue using cocaine. In fact, these rats liked cocaine and were willing to tolerate any adverse effects brought on by the drug. The cocaine-using rats showed a preference for areas that they associated with cocaine use.
In other words, junkie rats enjoy hanging out where drugs are used. Rats that don't use drugs don't want to hang around places where drugs are used, a sentiment any non-drugging human can certainly appreciate. Rats are actually very intelligent animals.
Differences were also evident in unmedicated rats that received cocaine as adults. While these rats did not show a preference to places associated with increased doses of cocaine, they did show an otherwise typical response to the drug. These rats did not show aversive responses to cocaine.
Conclusions
Anderson's research indicates that children who are given methylphenidate are less likely to develop substance abuse disorders as adults. According to this study, Ritalin and other stimulant medications, when used as prescribed in children, are not "gateway" drugs that lead to the use of cocaine of other drugs. On the contrary, giving children these medications appears to decrease their desire to use cocaine and other illicit drugs.
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