Research has suggested that the synthetic steroids delivered by the female contraceptive pill can shrink certain regions of the female brain and could also be altering their function.

In 2015, neuroscientists from the University of California, Los Angeles in the US took brain scans of 90 women who were either currently using the pill or not, and found that two key brain regions were thinner in pill users - the lateral orbitofrontal cortex and the posterior cingulate cortex.

These two regions are involved in emotion regulation, decision-making and reward response, and the researchers believe that their findings could help explain why some women become anxious or depressed when taking the contraceptive pill. 

"Some women experience negative emotional side effects from taking oral contraceptive pills, although the scientific findings investigating that have been mixed," lead author of the study, Nicole Petersen, told The Huffington Post back in 2015.

"So it's possible that this change in the lateral orbitofrontal cortex may be related to the emotional changes that some women experience when using birth control pills."

Although these findings were based on a very small sample size, scientists have previously shown that the pill can affect to whom a woman is attracted, and can halve the size of their ovaries.

And in 2010, a team from Austria also found that the contraceptive pill could change the shape of the brain regions associated with learning, memory and emotion regulation.

But their research suggested that it thickened those regions, rather than thinning them, a result that this new study contradicts.

However, it's important to note that the research didn't look into whether going on or off the pill changed brain shape within the same women. The researchers also haven't studied whether the effects are permanent or temporary.

Publishing their results in the journal Human Brain Mapping, they concluded:

"Further investigations are needed to determine if cortical thinning in these regions are associated with behavioural changes, and also to identify whether [pill] use is causally or only indirectly related to these changes in brain morphology."

But don't panic just yet. Even if the pill does turn out to shrink brain regions in certain women, there's no evidence that this is dangerous. But it's definitely cause for more research.

"The possibility that an accepted form of chemical contraception has the ability to alter the gross structure of the human brain is a cause for concern, even if the changes seem benign - for the moment," neuroscientist Craig Kinsey from the University of Richmond in the US, who wasn't involved in this research, commented in Scientific American, in reference to the Austrian study back in 2010.

"In any event, women need to have all of the medical and now, neurobiological, information they can use in informing their personal contraceptive decisions."

A version of this story was first published in April 2015.