For the 100 million women worldwide on the contraceptive pill, the side effects are familiar.
Mood swings, headaches and nausea, while more serious complications include blood clots and breast cancer.
But scientists in California have added another potential cause for concern to the check list.
Their new study has found the oral contraceptive shrinks two key regions of the brain, changing the way they function.
The findings suggest the synthetic hormones found in the Pill cause these alterations in brain structure and function.
Furthermore the ingredient is thought to suppress the natural hormones that occur when women take the Pill.
Neuroscientists at UCLA examined the brains of 90 women, 44 of whom took the Pill, and 46 who experienced natural cycles.
They found the lateral orbitofrontal cortex and the posterior cigulate cortex were thinner in those women taking the contraception.
The lateral orbitofrontal cortex plays an important role in regulating a person's emotions and their response to rewards.
As a result the changes noted by researchers could, they say, be responsible for increased anxiety and depressive symptoms experienced by some women on the Pill.
Meanwhile the posterior cingulate cortex governs the 'internal state', or inward-directed thought, helps process emotions and retrieve memories.
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Nicole Petersen, the study's lead author, told The Huffington Post: 'Some women experience negative emotional side effects from taking oral contraceptive pills, although the scientific findings investigating that have been mixed.
'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.'
Researchers said they do not yet know if these changes to the brain are permanent, or if they only last while a woman is taking the Pill.
Dr Petersen said more research is needed, but added that this study is the first step.
The latest study comes five years after research by the Royal College of General Practitioners revealed Pill-users have a 12 per cent reduction in their risk of developing cancer.
Scientists at UCLA found the lateral orbitofrontal cortex and the posterior cigulate cortex were thinner in those women taking the contraception. They believe it could account for increased anxiety and depressive symptoms experienced by some women taking the Pill
The researchers studied 46,000 women across four decades, and found those on the Pill were less likely to die of cancer, heart disease or stroke.
It contradicts past studies that have linked the Pill to breast cancer.
The risks associated with taking the Pill are increased if a woman smokes, has a family history of thrombosis, is severely overweight, diabetic, has a high blood pressure or high cholesterol level.
The study was published in the journal Human Brain Mapping.
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