If you thought regular hormones were bad, your birth control pill might just be making it worse. A new study designed by the researchers at the University of Copenhagen that currently includes more than 1 million women aged 15 to 34 found that birth control pills “may increase the risk of depression.”

According to Time, “They grouped the women into two main groups—users and nonusers of hormonal contraceptives. About 55% of the women were in the ‘user’ group, including anyone who’d been on birth control in the previous six months. (They were put in this group in order to include anyone who’d recently quit because of depressive symptoms.) The researchers followed the women for an average of 6.4 years.”

Users of birth control are well aware of the mood swings sometimes associated with a fresh prescription of pills, but if those mood swings don’t wear off or mellow within a few months, as most doctors say they should, “some women stop using birth control.” According to the researchers’ paper in JAMA Psychiatry, the fact that birth control is already well-known to cause these kinds of mood swings may be why doctors are not wholly concerned about the pill’s effect on emotional health.

“If woman feel depressed and take themselves off birth control, they’re less likely to be included in studies that could show a link.”

What Happened Next?

The study found that women who use the most common pill (those containing both estrogen and progestin) “were 23% more likely to have been prescribed an antidepressant” than those on another kind of pill or not using the pill.

In comparison, those on pills containing only progestin were 34% more likely. That’s over 10%.

Women taking other kinds of hormonal birth control were found to be even more at risk. When compared to women who did not take any kind of contraceptive, “antidepressant prescriptions increased by 40% for those using a progestin-only IUD (levonorgestrel); 60% for those using a vaginal ring (etonogestrel); and 100% for those using a patch(norgestrolmin).”

How Safe Is This Stuff?

Through the study, the authors’ theory that these hormones (particularly progesterone/progestin) may be a key player in the development of depression was proven correct. They found that the pill comparison tests were “especially telling,” while the “higher risk” among patch and ring users was probably due more to a difference in hormone levels than delivery method.

Teens who used a combination pill were 80% more likely to be prescribed antidepressants, while those on progestin were 120% more likely. If they took any other kind of non-oral method, their risk tripled.

However, most of the study’s participants were not affected. Only 12.5% of all participants (both users and nonusers) were prescribed antidepressants for the first time, and only 2% were diagnosed with depression for the first time.

How Accurate Can It Be?

Although the researchers were careful in their selection of participants and excluded anyone with prior depression diagnosis, they noted some limitations: “Not all depressed women are diagnosed or treated with antidepressants … and not all antidepressants are prescribed for depression.”

Øjvind Lidegaard, MD, a clinical professor and the lead author of this study, sat down with Health.com to discuss their findings in more detail:

“Women who develop depression after starting on oral contraceptives should consider this use as a contributing factor. Doctors should include these aspects together with other risks and benefits with use of hormonal contraceptives, when they advise women to which type of contraception is the most suitable for that specific woman.”

While this study is illuminating, you should talk to your doctor before making any decisions to stop using contraceptive methods.