Women who take birth control pills have a much higher level of the hormone oxytocin, also called the love hormone, in their blood compared to non-users, say researchers, adding that taking contraceptive pills is linked to a number of side effects, including mood alterations.
The current study, published in the journal Scientific Reports, helps understand why birth control pills affect emotional life.
"Oxytocin is a hormone found naturally in the body and is secreted during social cues and bonding, reinforcing social behaviour," said study researcher Michael Winterdahl from Aarhus University in Denmark.
"A constantly elevated level of oxytocin may mean that it is not secreted in the same dynamic way as under normal conditions. It is precisely these dynamics that are important to our emotional lives," Winterdahl added.
This may explain why feelings such as closeness, attachment and love appear to be altered in some women who use birth control pills.
For the findings, the research team collected and analysed blood samples from 185 young women in the US. Participants also answered a variety of questions about their mental well-being.
Many women have used birth control pills at some point in their lives. The study presents evidence for changes in the levels of oxytocin in response to birth control, providing a mechanism by which some women experience an altered mood.
Since oxytocin is important for attachment to a partner, one can imagine that the constantly elevated level is important - not only for the woman herself but also in the broader sense of the relationship, the researchers said.
The study suggests there may be changes in the behaviour of women who would not otherwise experience more traditional side effects.
"Humans are super social beings, we are able to put ourselves in the place of others, show empathy, fear loneliness and seek community - all driven by the brain's secretion of oxytocin," Winterdahl said.
"Even very small changes in brain oxytocin levels will affect the way we process emotions and thus how we interact with each other," he noted.