Study: Oxytocin Encourages Men in Relationships to be More Faithful

There are a lot of theories as to what the key to a long-lasting, exclusive romance is–trust, open and honest communication, mind-blowing sex. But maybe it could be as simple as the presence of a little molecule known as oxytocin.

A study published in the Journal of Neuroscience indicates giving men in relationships a dose of the “trust hormone,” oxytocin, causes them to physically avoid unknown, attractive women. While the connection between monogamy and oxytocin has already been demonstrated in previous studies, those studies focused exclusively on animal behavior. This new study is the first time a similar correlation between monogamy and oxytocin has been demonstrated with human test subjects.

“Men who received the placebo felt discomfort

closer to the woman than men who received oxytocin.”

The study itself was simple and focused on healthy, heterosexual males— half of whom were single and half of whom were in committed, monogamous relationships. Half of the 86 subjects received oxytocin through a nasal spray, while the other half received a placebo. After receiving their spray, the men were put in contact with an attractive woman. In some cases, the woman moved toward the man, while in other cases, the man moved toward the woman. But in all instances, the man was instructed to indicate when he felt slight discomfort with the distance between him and the woman. Men who were single or who were in committed, monogamous relationships and received the placebo felt discomfort closer to the woman than committed, monogamous men who received oxytocin (20-24 inches compared with 28-30 inches).

These results were consistent regardless of the woman’s behavior (making eye contact or averting her gaze), and oxytocin was found to have no impact on the distance the men found comfortable when approaching other men.

Oxytocin has long been known to promote trust and bonding between people, though this indicates oxytocin may act preferentially, increasing trust and bonding within existing relationships instead of increasing these qualities among strangers — even attractive strangers of one’s preferred sex.