Attention Deficit Drugs May Have Long-Term Effects

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Attention Deficit Drugs May Have Long-Term Effects

Mon December 8, 2003 12:29 AM ET

 

WASHINGTON (Reuters) - Drugs given to children to treat attention deficit

hyperactivity disorder could have long-term effects on their growing brains,

studies on rats suggest.

Several studies published on Monday show that rats given a popular ADHD drug

were less likely to want to use cocaine later in life, but also often acted

clinically depressed and behaved differently from rats give dummy injections.

While rats are different from humans, the studies suggest that doctors should

watch children for long-term effects, too.

In the United States between 3 percent and 5 percent of children are diagnosed

with attention deficit disorder, marked by reduced ability to concentrate,

difficulty in organizing and impulsive behavior.

Patients are commonly prescribed stimulants but the practice is sometimes

controversial.

William Carlezon of McLean Hospital and Harvard Medical School in Boston and

colleagues raised two groups of rats. One was given Ritalin, known generically

as methylphenidate, during the rat equivalent of pre-adolescence, while the

other was given a salt water injection.

When they matured, the rats were tested for " learned helplessness " -- how

quickly they gave up on behavioral tasks under stress.

" Rats exposed to Ritalin as juveniles showed large increases in

learned-helplessness behavior during adulthood, suggesting a tendency toward

depression, " Carlezon said in a statement.

But rats, which generally like cocaine, were less likely to eat it if they had

been give Ritalin.

Carlezon said he did not believe the effects were specific to Ritalin, made by

Swiss drug giant Novartis. It could instead be a general effect of stimulant

drugs, many of which act by increasing the activity of a key message-carrying

chemical called dopamine.

Higher dopamine levels could affect the way brain cells cement their connections

during development, Carlezon wrote in the Dec. 15 issue of the journal

Biological Psychiatry.

A team at the University of Texas Southwestern Medical Center at Dallas found

that adult rats were less responsive to rewarding stimuli and reacted more to

stress if they had been given methylphenidate as youngsters.

A third study done by a team at Finch University of Health Sciences/The Chicago

Medical School found changes in how dopamine neurons responded to

methylphenidate.

" These three studies remind us how limited our knowledge is of the neurochemical

and functional characteristics of the human brain during childhood and

adolescence and on the effects of psychotropic drugs on brain development, " Dr.

Thomas Insel, Director of the National Institute of Mental Health, wrote in a

commentary.

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