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, Yang says. 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.