Could birth control be turning you off, not on? For women on the Pill, a new study suggests this could be the case.

Hormonal contraceptives, say the Bonn University researchers, may blunt the effects of oxytocin, our natural “love hormone” which increases whenever we cuddle.

Back in 2013, a research team from the German university conducted an experiment to understand how a synthetic version of oxytocin might affect the extent men found women attractive. Working with 20 “bonded” heterosexual men, the researchers gave each a quick pump of nasal spray that contained a synthetic oxytocin treatment. Next, the men viewed photos of their girlfriends and other women and then rated each woman's attractiveness.

While the nasal spray increased the men’s view of their partner’s beauty, it had no effect on their perceptions of other women, whether strangers or familiar friends. Looking at fMRI scans taken during the experiment, the researchers also discovered oxytocin increased reward system activity in each man's brain whenever he viewed pics of his partner.

“Oxytocin may contribute to romantic bonds in men by enhancing their partner’s attractiveness and reward value compared with other women,” wrote the researchers.

But is the same be true for women?

Hormonal High

Fast forward nearly three years. The same research team (give or take a couple of members) decided to run the same experiment on women. This time they enlisted the help of 40 heterosexual women in their 20s, all of them saying they were “passionately in love” with their partners. Half of these women inhaled a nasal spray containing synthetic oxytocin, while the other half were given a placebo. Then, all the women ranked the attractiveness of their partners' photos along with other men.

Next, the experiment was run again with the two groups of women swapping places — those who previously received a placebo got the nasal spray and vice versa. Finally, the researchers observed the women's brain activity just as they had in their previous experiment conducted on men.

Given the oxytocin nasal spray, women found their partners to be 15 percent more attractive than when given a placebo. For women on the Pill, though, no similar change occurred; the oxytocin did not increase their perception of sexual attraction.

“Gonadal steroids could alter partner-specific oxytocin effects,” suggested the researchers. However, they do believe the link between oxytocin, a romantic partner’s attractiveness, and the brain’s reward center is generally the same for both genders under natural conditions.

Source: Scheele D, Plota J, Stoffel-Wagner B, Maier W, Hurlemann R. Hormonal contraceptives suppress oxytocin-induced brain reward responses to the partner’s face. Social, Cognitive and Affective Neuroscience. 2016.