Why Birth Control Pills Might Be Making You Feel Bad

For many women, birth control pills provide huge benefits. They protect against unplanned pregnancies, can reduce symptoms of PMS and other hormonal issues and might lower the risk of endometrial and ovarian cancer. But for others, oral contraceptives can also have a downside, and many women stop taking them once they start.

A new study may offer some insight into what’s going on with those not-so-satisfied customers. In a double-blind, placebo-controlled trial published in the journal Fertility and Sterility, Swedish researchers found that oral contraceptives had a small negative impact on women’s quality of life.

The pill used in the study contained a combination of ethinylestradiol (a type of estrogen) and levonorgestrel (a type of progesterone). It’s the most popular birth control pill in Sweden and several other countries, because it’s associated with the lowest risk of blood clots. It’s common in the United States, as well.

Researchers assigned 340 healthy women, ages 18 to 35, to take either birth control pills or a placebo for three months. (To avoid pregnancy, they were also advised to use a non-hormonal contraceptive.) In screenings before the study began, scores for depressive symptoms and overall quality of life were similar for both groups.

After three months, however, the women who’d been taking the active pills estimated their overall quality of life to be lower than those who had been taking placebos. Before treatment, about 35% of both groups reported moderate-to-severe distress in general well-being; afterward, that number rose to 38% in the placebo group, and 44% in the birth control group. Scores for self-control and vitality were also lower in the birth control group compared to the placebo group after treatment.

On the other hand, the researchers did not find an increase in depression or anxiety rates for either group; nor did they find a decrease in general health. (About 7% of both groups had moderate to severe depressive symptoms, both before and after the three-month period.) Previous studies have linked hormonal birth control to depression, however, including a 2016 Danish study of more than one million women.

Lead author Dr. Angelica Lindén Hirschberg, professor of women’s and children’s health at the Karolinska Institute in Stockholm, says that doctors know surprisingly little about oral contraceptives’ effects on women’s health, despite the fact that an estimated 100 million women around the world use them. There’s a need for more placebo-controlled studies, she adds, especially in the area of mental health and well-being.

As for why birth control pills may affect these areas, the researchers have several theories. Hormonal changes, like a decrease in testosterone or an increase in progesterone, may be involved. (Progesterone, they note, has been shown to have a sedative effect on the brain.) Side effects may also play a role: 21% of the women in the birth control group reported bleeding disturbances, anxiety and mood changes, acne or appetite changes, versus 12% in the placebo group.

Health.com: 7 Common Birth Control Side Effects

The study authors point out that the quality-of-life changes they observed were relatively small, and say their results should be interpreted with caution. But, they add, the findings could suggest significant effects among individual women—and may be a contributing cause to irregular use or stoppage of birth control prescriptions.

Dr. Charles Ascher-Walsh, director of gynecology and urogynecology at Icahn School of Medicine at Mount Sinai, agrees that the effect noted in the study is not very large from a clinical standpoint. “It only takes a few women in the study to feel worse to bring the averages down,” he explains.

Ascher-Walsh, who was not involved in the study, says the findings aren’t very surprising—especially considering that up to 40% of women do not continue on oral contraceptives once starting. “This may be for a variety of reasons,” he says, “but certainly some of them are going to be related to a poorer sense of well-being.”

In this study, he says, “it is likely that most of the women starting oral contraceptive pills felt the same or even possibly better, and the small percentage of those who felt worse would be the ones to stop the oral contraceptives here.”

In the U.S., birth control pills that combine etinylestradiol and levonorgestrel include Seasonale, Seasonique, Amethyst, Nordette, Levora, Portia and others. Because the researchers only tested one specific formula, their findings may not apply to pills or contraception options that use different combinations, or different types, of estrogen and progesterone.

Lindén Hirschberg says that the findings should not discourage doctors from prescribing birth control, but that they should discuss these potential effects with patients—“particularly with those who have previous experience of mood disorders,” she told Health.com via email.

Ascher-Walsh feels the same way. “It certainly isn’t a reason not to try it,” he says. “But a responsible physician should warn their patients that some women generally don’t feel well on the pill and, if this turns out to be the case, alternatives are available.”

This article originally appeared on Health.com