Antidepressants may go well beyond just easing the symptoms of depression; they may also make people less neurotic, U.S. researchers said on Monday.

The study of people who took GlaxoSmithKline’s Paxil, known generically as paroxetine, suggests the drug may treat factors such as neuroticism that make a person more likely to be depressed in the first place.

“Our data suggests that modern antidepressants work partly by correcting key personality risk factors of depression,” Tony Tang, a psychology professor at Northwestern University in Evanston, Illinois, whose study appears in the journal Archives of General Psychiatry.

People who are neurotic tend to experience negative emotions and be emotionally unstable, often experiencing wide mood swings in a day.

“It’s the basic tendency towards having negative emotions,” Tang said in a telephone interview.

He said many studies have suggested that people who are highly neurotic have a higher risk of becoming depressed.

There is also some suggestion that people who are extroverts - those who tend to be both socially outgoing and have a more positive outlook on life - are less likely to become depressed, Tang said.

Both personality traits are affected by levels of the brain chemical serotonin, which is the chief target of a large class of antidepressants known as selective serotonin reuptake inhibitors, or SSRIs.

Tang and colleagues looked to see if the SSRI Paxil, also sold under the brand Seroxat, had any effect beyond just treating depression symptoms.

They gave the drug to 120 volunteers with depression and compared their experiences to 60 people who underwent a type of therapy known as cognitive behavioral therapy and another group of 60 who took a placebo.

Their personalities and depression symptoms were assessed before and after treatment.

‘VERY DRAMATIC CHANGES’

After 12 weeks, all participants saw improvements in their depression symptoms, but those who took Paxil also saw significant drop in their neuroticism, and a marked increase in extroversion compared with those in the other groups.

“Patients taking paroxetine reported 6.8 times as much change on neuroticism and 3.5 times as much change on extroversion as placebo patients matched for depression improvement,” the authors wrote.

“Those are very dramatic, notable changes,” Tang said.

“At the beginning of the treatment, they were way out there. Their neuroticism was abnormally high. By the end of treatment, they moved back into the boundary of the normal range.”

He said many of the drugs in the SSRI class work largely the same way are likely to have the same effect.

Dr. Ian Cook of the David Geffen School of Medicine at the University of California Los Angeles, who was not part of the research team, said the findings may cause some doctors to rethink their assumptions about how antidepressants work.

“The conventional wisdom has been for many years that the changes in personality that one sees during treatment tend to be thought of as a reflection of getting the depression under control,” he said.

If confirmed in other studies, Cook said the findings could help better predict who is at risk for major depression and which patients may benefit from treatment.

SOURCE: Archives of General Psychiatry, December 2009.