By Christian Jarrett

Imagine the arrival of some high-tech brain device for treating mental health problems. It’s effective for many, but there’s an important side-effect. It changes your personality. Alarm ensues as campaigners warn that users risk being altered fundamentally for years to come. Now replay this scenario but replace the neuro-gizmo with good old-fashioned psychotherapy, and realise this: we’re talking fact, not fiction. A new meta-analysis in Psychological Bulletin has looked at 207 psychotherapy and related studies published between 1959 and 2013, involving over 20,000 participants, with measures of personality taken repeatedly over time. The analysis has found that just a few weeks of therapy is associated with significant and long-lasting changes in clients’ personalities, especially reductions in the trait of Neuroticism and increases in Extraversion.

Talk of personality change can sound unsettling because we think of our personalities as reflecting our essential “me-ness”. But from a wellbeing perspective, the trait changes uncovered by this new research are welcome and may even underlie the benefits of therapy. Neuroticism or emotional instability is an especially important risk factor for future poor mental and physical health, and meanwhile high scorers on Extraversion are known to be happier on average and more optimistic.

The authors of the new research, Brent Roberts at the University of Illinois, Urbana-Champaign, and his colleagues, also report that personality change appeared to occur remarkably quickly. Roughly four or more weeks of therapy was enough to induce meaningful change. In fact, beyond eight weeks, more therapy was not associated with greater personality change. Therapy-related changes to trait Neuroticism were especially significant – a few weeks of therapy led to about half the amount of increase in emotional stability that you would typically expect to see someone exhibit over an entire lifetime (as a general trend, most of us slowly but surely become more emotionally stable as we get older).

Roberts and his team were particularly interested in whether the therapy-related personality changes they uncovered simply reflected an effect of mood or a genuine change in traits. Consistent with the idea that these were true trait changes, they found that personality change was larger in participants in treatment groups compared with those in control conditions, and that changes were found to last over the course of years without fading.

The researchers also uncovered a small number of “non-clinical” trials that involved healthy participants undertaking cognitive training and other interventions rather than psychotherapy, and that measured personality over time. Here too there was evidence of significant personality change, again arguing against the idea that the effects of psychotherapy on personality merely reflect a return to a non-depressed mood or to one’s natural personality pre-illness. However, Roberts and his team cautioned there were only a few of these non-clinical trials and they tended to be conducted over short time scales, so the question of whether psychotherapy is transforming a client’s personality or “remaking” it to an earlier state remains open for now.

Other details to emerge from the analysis: extent of observed personality change was about the same for different kinds of therapy, for instance be that CBT or psychodynamic (though hospitalisation was associated with the least amount of change); clients diagnosed with depression or personality disorders exhibited the greatest personality change compared with other conditions; and the size of the effects were the same across gender and age. This last finding concerning age is especially intriguing. As the researchers said, it appears to support “the plasticity principle that personality is an open system and amenable to change” through the lifespan.

There are some notable limitations to the new analysis, especially the fact that the studies under review almost entirely relied on clients’ ratings of their own personalities (though the fact that not all traits changed positively in response to therapy argues against a general effect on self-presentation or personality-related self-esteem). The research also leaves unanswered a big question for the future: just how is psychotherapy enacting these personality trait changes?

Cautions noted, this important paper shines a welcome light on a little discussed consequence of psychotherapy, and it feeds into a broader movement in clinical psychology that is recognising the important role of personality in mental health. In the near future we may see the development of therapeutic interventions that more deliberately target personality trait changes, rather than these changes being a kind of side-effect. The research also speaks to an ongoing debate in personality science about just how much personality changes, with the new findings arguing against the idea that change can only ever occur slowly.

“Personality traits are not only robust predictors of important life outcomes, but also appear amenable to intervention,” Roberts and his team concluded. “This fact opens the door to a new era of research that more strongly links personality and clinical psychology, and other groups, such as educational psychologists and economists, who are interested in changing people and their behaviours in order to help them with their lives.”

—A Systematic Review of Personality Trait Change Through Intervention

Christian Jarrett (@Psych_Writer) is Editor of BPS Research Digest