As our lives all too often show, love and envy are two sides of the same coin. An Israeli scientist has now proven that they are two sides of the same hormone as well. Dr. Simone Shamay-Tsoory, who conducted her research at the University of Haifa, has discovered that the same mammalian hormone involved in labor, delivery, lactation and love can also evoke negative behaviors such as jealousy and gloating. Oxytocin is best known as the "love hormone" for its ability to trigger empathy, generosity and trust. But after testing 56 volunteers, Shamay-Tsoory found that there was a fine line between love and jealousy - and that oxytocin could also bring out antisocial behaviors. Her study was published in the latest issue of Biological Psychiatry. "Subsequent to these findings, we assume that the hormone 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 explained. Previous studies have shown that the hormone has a positive effect on positive feelings. It is released in the body naturally during childbirth and when engaging in sexual intercourse. Participants in an experiment who inhaled the synthetic form of the hormone displayed higher levels of altruistic feelings, and it is suggested that it plays an important role in the formation of relationships between people. However, in earlier studies carried out with rodents, it was found that the hormone was also related to higher levels of aggression. Therefore, it was decided to examine whether the hormone also affected negative social sentiments. In the new study, done on humans, half of the participants inhaled the synthetic form of the hormone in the first session and were given a neutral placebo in the second session; the others were given a placebo in the first session and oxytocin in the second session. After the drug was inhaled, each participant was asked to play a game of luck along with another competitor, who was in fact - and without their knowledge - a computer. Each of the participants was asked to choose one of three doors and was awarded the sum of money hidden behind that door. Sometimes the participant gained less money than the other player, and sometimes more, creating conditions in which a person might develop feelings of envy and gloating. The findings showed that those who had inhaled oxytocin displayed higher levels of envy when the opponent won more money and of gloating when they were ahead. As soon as the game was over, no differences between the participants were evident with regard to these sentiments. This indicated that the negative feelings were empowered only in the course of the game itself. "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. "The results of the present study show that the hormone's undesirable effects on behavior must be examined before moving ahead," Shamay-Tsoory concluded.