Copenhagen – A large study made on Danish women stated that combined contraceptive pills are likely to trigger depression.

Medical records of more than a million women found that those on the combined pill were more likely to be prescribed an antidepressant by their doctor, most commonly after starting on the pill for the first time, compared with those not on hormonal contraception.

Adolescent girls appeared to be at highest risk. Those taking combined pills were 80% more likely and those on progestin-only pills were more than twice as likely to be prescribed an antidepressant than their peers who were not on the pill.

Researcher, Øjvind Lidegaard of the University of Copenhagen said there haven’t been a study on this subject as big as this one before.

The authors call for more studies to investigate this possible side-effect of the pill.

Researchers said women are twice as likely to suffer from depression in their lifetime as men, though rates are equal before puberty. They also believe the fluctuating levels of the two female sex hormones, oestrogen and progesterone, have been implicated, adding that studies have suggested raised progesterone levels in particular may lower mood.

They used registry data in Denmark on more than a million women and adolescent girls aged between 15 and 34. They were followed up from 2000 until 2013 with an average follow-up of 6.4 years, expect for women who were diagnosed with depression before 2002.

Women on the progestin-only pills, a synthetic form of the hormone progesterone, were 34% more likely to take antidepressants or get a first diagnosis of depression than those not on hormonal contraception.