Scientists have discovered a problematic link between the use of birth control pills and increased mind wandering, a potential risk factor for depression.

Half a century after its inception, the birth control pill remains the most popular contraceptive in industrial countries, with 82 percent of women using it at some point in their lives.

Recently, however, there have been strong indications that all types of hormonal contraception, including the pill, are associated with a greater risk of depression and antidepressant use.

While this is certainly worrisome and needs to be researched further, it doesn't mean that every woman who takes hormonal contraception will become depressed. Millions of women use hormonal birth control without ever developing a mood disorder, so there's no need for doctors to stop prescribing it.

Still, if we want to give women the best and safest contraception, it's important that we know what makes some of us more vulnerable to the depressive effects of birth control than others. New research suggests mind wandering might be one such factor.

Mind wandering is exactly what it sounds like. It's a cognitive state in which an individual's attention is distracted from the task at hand, focusing on thoughts and images that are irrelevant.

All of us do this to an extent; it's quite common to slip in and out of concentration. But sometimes this type of thinking can spiral out of control, and recent studies suggest this could set the stage for future mood disorders.

The current study compared both the frequency and nature of mind wandering by giving questionnaires to 28 healthy women on oral contraceptives (OC), 14 naturally cycling women, and 29 men.

All of the participants were between the ages of 18 and 35, and women who were using antidepressants or had received a psychiatric diagnosis were excluded from participating.

While women reported a greater frequency of mind wandering than men in the study, this was not because of some inherent difference between the sexes. Instead, it appears the trend was being driven predominantly by women who use oral contraceptives.

"Indeed, we found that the increased frequency of mind wandering is only present in oral contraceptive users, and that naturally-cycling women do not differ from men," the authors write.

"In fact, on all measures of mind wandering (frequency or nature), we found that naturally cycling women present similar levels of mind wandering as men."

The findings suggest that women who use birth control pills tend to have less control over their attention spans and have trouble concentrating on tasks. And even though this may seem harmless, it could have serious implications.

The new findings look remarkably similar to the pattern of depression found in extensive, high quality studies of the pill - where, in general, women who are on oral contraceptives appear to be more vulnerable to depression.

Furthermore, mind wandering itself has been linked to the severity of depression. Previous research has shown that increased lapses in concentration are linked to negative thinking and mood disorders like depression.

"… our results suggest that an increase in the frequency of mind wandering in OC users could serve as a marker of risk for depressive disorder in women," lead author Catherine Raymond, a researcher in behavioural science at the University of Montreal, told PsyPost.

The conclusions that can be drawn from this study, however, are limited. The research only identified correlations, which means we still aren't sure if a wandering mind leads to an unhappy mind, if the thought process is just a symptom of depression, or if it simply goes hand in hand with depression.

Interestingly, this particular study did not find depression to be more common among women who took the pill, although the frequency of mind wandering was strongly correlated with depression scores.

The authors think this might have occurred because they excluded women with clinical depression from study, and the questionnaire used was not sensitive enough to pick up on pre-clinical mood disorders.

To make sense of their findings, the researchers have proposed a "brain vulnerability hypothesis." It suggests that the hormones in oral contraceptives can change the brain functions and structures that make young women more vulnerable to mind wandering and/or depression - however the two may be connected.

"Since synthetic sex hormones that are contained in oral contraception also access the brain, we think that more studies are needed to understand the effect of oral contraceptives on the developing brain," Raymond told PsyPost.

This study has been published in Psychoneuroendocrinology.