A researcher at the University of Haifa has discovered that the hormone oxytocin, also known as the "love hormone," can trigger negative emotions such as jealousy as well.

Oxytocin is released naturally in the body during childbirth, lactation and when engaging in intimate relations. Participants in a previous experiment who inhaled a synthetic form of the hormone displayed higher levels of altruistic feelings. However, it was also discovered in earlier studies on rodents that the hormone may be linked to higher levels of aggression as well.

"Following the earlier results of experiments with oxytocin, we began to examine the possible use of the hormone as a medication for various disorders, such as autism," explained Dr. Simone Shamay-Tsoory, who led the study. However, "The results of the present study show that the hormone's undesirable effects on behavior must be examined before moving ahead."

The study, published in the professional journal Biological Psychiatry, included 56 subjects, half of whom inhaled the synthetic form of oxytocin in the first session and were given a placebo the second time around. The other 28 participants were given a placebo the first time and the real hormone in the second session.

Following administration of the hormone, each participant was asked to play a game of luck together with another competitor, one who, without their knowledge, was a computer. Sometimes the participant won more money than the other player, sometimes less, creating conditions in which a player could develop feelings of envy or gloating.

The findings showed that participants who inhaled the "love hormone" exhibited higher levels of envy when their opponent won more money and gloated more when they were ahead. But as soon as the game was over, no differences were noted between the participants' emotional levels, indicating that the negative feelings were empowered only during the activity.

Shamay-Tsoory, who led the study, said that the findings have led her team to assume that oxytocin is an overall trigger for social sentiments. "When the person's association is positive, oxytocin bolsters pro-social behaviors; when the association is negative, the hormone increases negative sentiments," she said.