Oxytocin developed its reputation as 'the love hormone' for several reasons: It helps women lactate and give birth. It makes people more sociable. It floods bodies and minds during orgasms. And it increases peoples' feelings of love and trust of those around them.

Or maybe not. It turns out that, as far as love goes, oxytocin isn't for everyone.

This surprising result and its major implications for psychiatric treatment follow from a new study by psychologist Jennifer Bartz and her colleagues at the Mount Sinai School of Medicine in New York City.

Fourteen of the study's subjects had previously been diagnosed with borderline personality disorder, a condition marked by mood swings, extreme insecurity, fear of abandonment and impulsive decision-making. The other 13 participants were clinically normal. The researchers had each subject inhale either a dose of oxycotin or a placebo , then play video games in which he or she had to cooperate with a volunteer.

It was a game of trust: If two players won together, they'd get $6 each. But either player also had the choice to quit the game and claim $4 for himself alone.

For test subjects who were clinically normal, as expected, oxytocin acted to amplify feelings of trust and social camaraderie. Compared to those who had taken placebos, loved-drugged participants were more likely to think the best of their game partner, work together with them and earn $6.

However, for subjects with borderline personality disorder, the opposite was true. Those under the influence of oxytocin became significantly more suspicious of their partners. Considering it likely their partners would throw in the towel and make away with the award money, they would act preemptively by quitting the game and claiming the money for themselves first.

In other words, if you tend to trust others, oxytocin will make you trust them more. If, on the other hand, you carry around social anxiety and suspicion, oxytocin will amplify those feelings instead.

This result flies in the face of psychiatrists who have pushed for oxytocin to be used to treat autism and other conditions involving social difficulties.

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