Dec. 7, 2009 — Besides treating depression, the antidepressant Paxil may affect personality traits in positive ways, a new study suggests.

Researchers say Paxil and likely other antidepressants in the class of drugs called selective serotonin reuptake inhibitors (SSRIs) may improve higher levels of neuroticism and lower levels of extraversion that are commonly seen with depression.

Neuroticism is characterized as being inclined to have negative emotions such as anxiety, hostility, self-consciousness, impulsivity, and sensitivity to stress.

Extraversion refers to being inclined to have positive emotions, assertiveness, and gregariousness.

Paxil May Affect Personality

In a placebo-controlled trial involving 240 adults with moderate to severe depression, 120 patients in the study took Paxil, 60 underwent cognitive therapy, and 60 took placebos for eight weeks.

In weeks 9-16, half of the participants on placebo were given Paxil. Then there was a 12-month phase when half of those in the Paxil group stayed on Paxil and half were taken off Paxil and given placebo pills.

Personality variables and depression were monitored through the study period.

All patients showed less depression at week 8, the researchers report in the December issue of Archives of General Psychiatry.

Paxil reduced neuroticism and increased extraversion, says study researcher Tony Z. Tang, PhD. Both traits have been linked to the brain’s serotonin system, which is targeted by Paxil and other SSRIs.

Neuroticism and Extraversion

Many, if not most, people experience some of neuroticism’s personality traits, including a tendency to see things in a negative light and unusual anxiety and fearfulness, one of Tang’s collaborators, Robert J. DeRubeis, PhD, of the University of Pennsylvania, tells WebMD.

In addition, he tells WebMD, the patients in the Paxil group became more extraverted, meaning they became more open to new experiences, calmer, less self-conscious, and more even-tempered.

The researchers say their findings provide evidence against a theory known as the “state effect hypothesis,” which proposes that any personality changes during SSRI treatment occur only because they alleviate symptoms of depression.

“One possibility is that the biochemical properties of SSRIs directly produce real personality change,” the researchers write. “Furthermore, because neuroticism is an important risk factor that captures much of the genetic vulnerability for major depressive disorder, change in neuroticism and in neurobiological factors underlying neuroticism might have contributed to depression improvement.”

If further research can repeat the findings, it means that “there are important and noticeable effects of the medicine that have gone undetected,” DeRubeis tells WebMD. “And the findings are consistent with the idea that the medicines work more by affecting neuroticism and extraversion … whereas we have always thought that these personality variables, though mostly stable, go up and down as depression waxes and wanes.”

Paxil’s Potent Punch

DeRubeis says they found that “the effects [of Paxil] on personality are quite potent,” which made it easier for depressed patients to feel positive emotions.

The researchers write that patients taking Paxil “reported 6.8 times as much change on neuroticism and 3.5 times as much change on extraversion as placebo patients matched for depression improvement.”

Patients taking Paxil became “less shy, more vivacious … less sensitive to rejection” and stress and generally felt more stable emotionally, Tang tells WebMD.

“To most psychiatrists our findings would be very surprising,” he says. “They traditionally think of [SSRIs] as antidepressants first and foremost, and the effect on personality as negligible or by-products of depression improvements,” Yang says. “We are now finding that the effect on personality is very substantial and clearly not a by-product of depression improvement.”

He tells WebMD the results “may make many people uncomfortable” because they raise “the possibility of using these drugs to normalize personality for millions of non-depressed people.”

DeRubeis tells WebMD the study suggests that “important and noticeable effects” of SSRIs have gone undetected.

“The magnitude of change in personality was markedly larger than that observed in the standard measures of depressive symptom severity,” and patients taking placebo “did not evidence the change in personality that would be expected if change in depression caused change in personality.”

Depression ‘More Than Just Mood’

Claude Robert Cloninger, MD, a professor of psychiatry, genetics, and psychology at Washington University in St. Louis, tells WebMD that the conclusions of the new study “confirm earlier work showing that particular personality traits are indicators of vulnerability to depression.”

However, the Tang study “is new in that it … focuses on the improvements in personality resulting from antidepressant treatment. Being less neurotic and more extraverted is a healthier and happier profile.”

“What this work does well is show” that depression is “not just a matter of mood” and that SSRIs “are not specific just for depression,” Cloninger tells WebMD.