From Our 2006 Archives

Animal Study Links Teen Aggression With Prozac

By Amanda Gardner
HealthDay Reporter

MONDAY, Oct. 16 (HealthDay News) -- Scientists have uncovered clues as to why children and adolescents may get more aggressive or even suicidal while taking the widely prescribed antidepressant Prozac.

A new study has found that juvenile hamsters became aggressive on low doses of Prozac (fluoxetine) but less aggressive on high doses. By contrast, adult hamsters were calm on both high and low doses of the drug.

The bottom line: Adult and juvenile brains are different.

While intriguing, the study has some clear limitations, experts cautioned.

"Just remember that a hamster is a hamster is a hamster," said Dr. Jon Shaw, director of child and adolescent psychiatry at the University of Miami Miller School of Medicine.

Which is not to say that the findings don't have some value.

"There are a lot of studies on the maturation and evolution of the central nervous system structure through adolescence, and nobody thinks the adult brain is [the same as] the child's brain. And this just reminds us that other studies are needed to try and understand what the difference means in terms of metabolism of drugs," Shaw added.

Pediatric use of antidepressant medications -- especially a newer class of drugs called selective serotonin reuptake inhibitors (SSRIs), of which Prozac is a member -- has been the subject of extended controversy.

In October 2004, the U.S. Food and Drug Administration directed manufacturers of SSRIs, which include Celexa, Paxil, Prozac and Zoloft, to put a special "black-box" warning on the drugs' labeling. The warning alerts health-care providers about an increased risk of suicidality in children and teens using the medications.

In July 2005, the FDA issued a public health advisory that raised the possibility that the risk of suicidality also applied to adults taking SSRIs, after several studies pointed to that possibility.

Other studies, however, have found a lower incidence of youth suicide related to Prozac and other SSRIs. Prozac is the only medication approved to treat depression in children and adolescents.

For the new study, which was published in the October issue of Behavioral Neuroscience, researchers at the University of Texas at Austin injected hamsters with either high or low doses of Prozac.

Two hours later, they created a threatening situation by putting a younger hamster in the home cage of another same-sex hamster for 10 minutes. Usually, male hamsters will respond to such situations with aggression.

In these scenarios, the adult hamsters injected with either the high or low dose of Prozac were calmer. Juvenile hamsters, however, reacted differently to the different doses. Those on low doses were more aggressive while those on higher doses were less aggressive, though still not as calm as the adults.

"We do know from adolescent studies that the brain continues to mature during adolescence, and even the early adult years," Shaw said. "So, this study is an important study in that it reminds us that further research is really necessary to look at how an evolving central nervous system responds to different stimuli."

The study authors also pointed out that teens may have lower levels of the neurotransmitter serotonin in their system than adults, and it might not be enough for an SSRI to work with.

It's also possible that some teens who become more aggressive and/or suicidal while taking SSRIs may have an unusual reaction to the drugs.

"There is this paradoxical situation that the use of antidepressants reduces suicidal behavior both in adolescents and adult and, at the same time, there are some idiosyncratic situations where some individuals are more hyper aroused and possibly more aggressive," Shaw said.

SOURCES: Jon A. Shaw, M.D., professor and director, child and adolescent psychiatry, University of Miami School of Medicine; October 2006 Behavioral Neuroscience

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