A hormone that encourages women to befriend another person may boost the placebo effect, according to a new study. Vasopressin, which research suggests makes men more anxious and competitive, may have made women in the study relax and feel more at ease and trusting. The results were published online last month in Biological Psychiatry.

Last year, researchers examining the so-called cuddle hormone oxytocin found that the chemical enhanced the placebo effect in an all-male trial. Luana Colloca at the University of Maryland in Baltimore wondered if vasopressin—which elicits a tend-and-befriend response in women—might have a similar effect since both hormones are linked with social interaction.

Colloca gave electric shocks to the fingers of 109 men and women. She adjusted the level of each shock so the individual rated the pain as moderate. Then the participants were asked to take a sniff of vasopressin, oxytocin, salt water or nothing. After the sniff, Colloca told the volunteers that when they saw a green light, the shock would be reduced, but if they saw a red light, the level would stay the same. In reality, the intensity of the shock never changed. The research team compared the responses for the red light and the green light. The differences represent the placebo effect—the participants thought they felt less pain because they saw a green light, but they were given the same shocking treatment.

Everyone experienced the placebo effect. But the women who were given vasopressin showed the biggest change between the pain they thought they were feeling and the pain they reported with the first electric jolt.

Colloca’s team concluded that vasopressin nose spray made women relax and feel a sense of connection with the researcher delivering the shock, which made the placebo even more effective. The results show that naturally produced hormones could be causing the placebo effects that show up in some clinical trials, and this new information could help scientists factor in the effects of hormones in future studies.

Researchers also hope these findings could be used to make medical treatments more effective—either by using hormone therapy alongside a patient’s regular medications or by improving the relationship between a woman and her doctor.

“We know the best care providers interact well with their patients,” Colloca told New Scientist. “It might be possible to help a person control their pain by enhancing this cooperation response.