According to Tony Z. Tang, Ph.D. of Northwestern University, neuroticism and extroversion are two personality traits linked especially closely to depression risk, because they are affected by the brain's serotonin system. These neurological processes are also the target of a popular class of antidepressants known as serotonin reuptake inhibitors (SSRIs).
Neurotic individuals, who tend to experience negative emotions and emotional instability are more likely to experience clinical depression than extroverts, who are more socially outgoing and dominant, writes Tang.
Relief from the symptoms of depression may decrease introversion and increase extroversion. But Tang's team wondered if the antidepressant medication itself could be causing at least some of these personality changes.
To highlight changes in neuroticism and extroversion that might be caused by the treatment of depression with SSRIs, Tang and his colleagues studied the effects of the SSRI paroxetine
on 240 adults with major depressive disorder in a randomized, placebo-controlled trial. For 12 months, 120 participants took paroxetine, 60 received cognitive therapy, and 60 took a placebo.
The personalities and depressive symptoms of all the participants were assessed before, during and after treatment.
The team found that symptoms of depression improved for all three groups.
However, after assessing and allowing for the control group's improvements, personality test results showed that individuals who took paroxetine reported 6.8 times less neuroticism and 3.5 times more extroversion than placebo patients with similar improvements in their depressive symptoms.
Patients in the paroxetine group also showed significant increases in extroversion and decreases in neuroticism when compared with the cognitive therapy group.
Tang and his colleagues note that their findings contradict the state effect hypothesis, which attributes personality changes that appear during SSRI treatment entirely to the relief of depressive symptoms.
The authors write that further investigation into how SSRIs change personality and its underlying neurobiology could lead to better understanding of how these often prescribed drugs work to alleviate depression as well as improve other conditions associated with high neuroticism and low extroversion, such as anxiety and eating disorders.
"One possibility is that the biochemical properties of SSRIs directly produce real personality change," Tang's team concludes.
This research appears in the December 2009 issue of the JAMA and Archives journal
, Archives of General Psychiatry