FRIDAY, Dec. 2 (HealthDay News) -- The antidepressant Prozac may help ease repetitive behaviors in some adults with autism, a new study indicates.

Researchers randomly assigned 37 adults with autism to take either Prozac (fluoxetine) or a placebo for 12 weeks. The study participants had difficulties with repetitive behaviors, such as arm flapping, as well as issues with restricted interests or agitation when their routines were disrupted, explained senior study author Dr. Eric Hollander, a clinical professor of psychiatry and behavioral sciences at Albert Einstein College of Medicine and director of the Autism and Obsessive-Compulsive Spectrum Program at Montefiore Medical Center in New York City.

After three months, 50 percent of the group receiving fluoxetine showed a reduction in repetitive behaviors as assessed using a scale that measures obsessive-compulsive symptoms compared to 8 percent in the placebo group. In addition, 35 percent on fluoxetine showed an overall improvement in their autism symptoms compared to none in the placebo group.

"What is unique about this study is that there have been very few studies on adults with autism -- most of the work has been done on children," Hollander said. "The second important point is that we stratified the population. We wanted to get people who had a lot of repetitive behaviors and had a lot of room for improvement."

The study, which was funded by the U.S. Food and Drug Administration, is published online Dec. 2 in the American Journal of Psychiatry.

Autism is a neurodevelopment disorder characterized by problems with social interaction, communication and restricted interests and behaviors. That includes repetitive behaviors; having an obsessive interest in one topic; having a need to stick to a specific ritual or routine; and experiencing distress or agitation when that routine gets disrupted.

Currently, antidepressants aren't uncommon in treating repetitive behavior in people with autism, but their use is considered "off-label" because none have been approved by the FDA for use in treating autism.

Several prior trials have tried to determine it selective-serotonin reuptake inhibitors (SSRIs) such as Prozac could help alleviate repetitive behavior, but those have largely been done in children, said Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Steven and Alexandra Cohen Children's Medical Center of New York.

"This is a nicely designed study that showed fluoxetine to be helpful in reducing repetitive behaviors in adults with autism," Adesman said, with the caveat that only half of the people in the study saw improvement.

Prior research on SSRIs and autism have had mixed results. A multi-center study published in 2009 found fluoxetine was no more effective than a placebo in reducing repetitive behaviors in children and adolescents aged 5 to 17 with autism.

A 2009 trial of another antidepressant, Celexa (citalopram), also concluded the drug did not reduce repetitive behaviors in children with autism spectrum disorders. Some of the children on citalopram also experienced side effects, including agitation and sleeplessness, said Hollander, who was an investigator on that research.

In adults, a prior study found another antidepressant, Luvox (fluvoxamine), also may have benefited some adults with autism, Adesman added.

It's important to keep in mind that SSRIs may behave differently in adults than in children, and that not all SSRIs are the same, Hollander noted. Moreover, his research suggests that SSRIs may have the most effect in adults who are experiencing significant repetitive symptoms.

"Adults with autism have been overlooked. Most of the focus has been on children, but children with autism grow up to be adults with autism," Hollander said. "This is one of the very few studies that shows you can intervene at later ages and get improvement."

More needs to be learned about SSRIs and autism, Adesman said.

"What this study seems to suggest is that maybe not all SSRIs are the same and when it comes to treating symptoms, just as all individuals aren't the same, it may be a matter of identifying which agents to use and which patients will benefit," he said.

More information

The U.S. National Institute of Mental Health has more on autism.