http://www.sciscoop.com/story/2003/12/11/71243/827
New Studies Claim Ritalin Used For ADHD Causes Permanent Brain Alterations
From an NIH press release: 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.
In an editorial accompanying the Brandon, Carlezon, and Bolaños papers, Dr.
Nora D. Volkow, director of the National Institute on Drug Abuse (NIDA), and
Dr. Thomas Insel, director of the National Institute of Mental Health (NIMH),
both components of the National Institutes of Health, articulate the important
contributions of these studies as well some of the caveats that need to be
considered before these results can be applied to humans. Importantly, the
studies show changes in the function of brain dopamine cells and in behavior
following chronic exposure to doses of methylphenidate similar to those used to
treat ADHD in children.
ADHD affects an estimated 3 to 5 percent of school-age children around the
world and is considered to be the most prevalent psychiatric disorder of
childhood. Among the caveats noted by Drs. Volkow and Insel in their editorial,
is the way in which the drug is administered to rats (by injection into the
abdominal cavity) compared to the oral route (by tablet) used by humans. This
could lead to differences in how much and how quickly the drug affects the
brain. In addition, for these studies to be truly applicable to ADHD, they may
need to be carried out in an animal model of the disorder, rather than in
normal rats. Thus, the results may be more applicable to children and
adolescents who do not have ADHD, but who take stimulants for non-medical
purposes, or to those who are treated with stimulants as a result of
misdiagnosis. This underscores the importance of proper diagnosis of this
disorder.
Drs. Volkow and Insel further state: "Because the use of stimulant medications
for the treatment of ADHD has increased significantly over the past 10 years,
it is vitally important that we evaluate the long-term effects of these drugs
in the human brain and on behavior. Such knowledge is essential for a better
understanding of ADHD and its management, and will help inform those with ADHD
and their relatives about the risks and benefits of stimulant medications."