Personality, once thought to be fundamental and resistant to change, can shift in response to therapy, new research finds.

The study synthesizes data from 207 published research papers that measured personality traits as one outcome of various psychotherapies. Though most of the research was observational rather than experimental, the review, which was published on Jan. 5 in the journal Psychological Bulletin, adds new weight to the idea that personality is not static .

But that doesn't mean that personality change is easy, warned study researcher Brent Roberts, a social and personality psychologist at the University of Illinois.

"For the people who want to change their spouse tomorrow, which a lot of people want to do, I don't hold out much hope for them," Roberts said. However, he continued, "if you're willing to focus on one aspect of yourself, and you're willing to go at it systematically, there's now increased optimism that you can affect change in that domain."

More From LiveScience

Consistency or change?

Previous research has found that the "big five" personality traits — openness to experience, conscientiousness , extraversion , agreeableness and neuroticism — are predictive of success in life.

And much research has suggested that these traits are stable. For example, one 2010 study showed that people's personalities were relatively stable from first grade to adulthood , and that a first grader's personality could predict his or her adult behavior, the review said. People who were impulsive as kids were likely to be talkative and expansive in their interests as adults, while those who were more restrained as children grew up to be more insecure and timid.

Studies such as that one have led some researchers to view personality as basically immutable. But other scientists have challenged that notion, including Roberts in his own research. For example, he and his colleagues found that people become more conscientious and emotionally stable during young adulthood and midlife. Openness to new experience increases in the teen years and declines in old age.

If personality can change, even late in life, Roberts told Live Science, the natural next question was whether a person could change his or her personality deliberately . Some research analyzed in the review suggested that even surprisingly short-term interventions might do just that.

In 2009, for example, researchers at Northwestern University in Illinois found that antidepressants make people more extraverted and more emotionally stable . And a 2011 study found that a single dose of psilocybin, the hallucinatory compound in "magic mushrooms," can increase people's openness to experience for at least 14 months , which is considered a long-term change.

Gold mine of data

When Roberts and his colleagues first became interested in looking at whether interventions can change personality, they expected to find few studies to analyze, because personality psychologists don't typically focus on altering personality , Roberts said.

"I thought we could do this pretty quick, which, you should never say that as an academic," Roberts said.

To his surprise, Roberts said, he found what he called a "gold mine" of data on personality change. It came from an unexpected source: clinical psychology. While personality psychologists had more or less neglected the question of how to change personality, clinical psychologists had been measuring personality change that resulted from therapy and psychiatric medications all along, but almost as an afterthought.

"Most of the literature is [asking], 'Does this version of cognitive behavioral therapy work better than that version of cognitive behavioral therapy for anxiety ?'" Roberts said. "It's usually something very specific to a clinically motivated agenda … [but] in the process, they measure a bunch of different things."

Those things included personality. The biggest changes, Roberts and his colleagues found, were in people's levels of neuroticism . This trait is marked by jealousy, fear, anxiety and other negative emotions. People typically become less neurotic as they age, Roberts said. The new analysis found that three months of psychological treatment could also significantly lower neuroticism , by about half the amount you might expect to see over 30 to 40 years of adulthood.

"One way to look at that is you get half of a life in a three-month period," Roberts said. "I honestly did not expect to see effect sizes that large."

Another personality trait, extraversion, also showed significant, though smaller, changes after psychological interventions . The type of therapy used didn't seem to matter, the researchers reported Jan. 5 in the journal Psychological Bulletin, though psychotherapy was associated with slightly larger changes in personality than drug therapies alone. Hospitalization for psychiatric problems did not result in any personality changes, the researchers found.

Trait vs. state

One key question is whether the changes were representative of a change in fundamental personality traits versus simply a shift in psychological state, or mood , Roberts said. A person's mood, for example, can affect how he or she responds to questions about his or her personality.

"If you're in a bad mood and I force you to take a 150-item personality inventory, you might not respond well," Roberts said.

Complicating matters, few of the studies available were true experiments that randomly assigned patients to treatment and control groups. Those studies that were experimental, however, did show significantly larger effects on personality in the treatment group compared with the control group, the researchers found. And in the observational studies, follow-ups that took place months or years after treatment showed no evidence that people were backsliding: The changes that followed therapy stayed stable, suggesting that these are changes in people's basic personality traits rather than moment-by-moment moods, the researchers said.

Still, more studies with long follow-up periods need to be done in order to really test the idea that personality can be changed, Roberts said. Ideal research, he said, would include randomly assigning patients to treatment as well as getting outside observers, like friends or family, to rate any personality changes. A perfect study would also follow people for several years after the treatment, Roberts said.

A further question is what is the "magic ingredient" in therapy that ushers in personality change, Roberts said.

"If you can actually affect change in something like neuroticism or conscientiousness," he said, "you could possibly have pretty interesting consequences for somebody, because personality traits are important."

Original article on Live Science.