Young women using hormone-based contraceptives, including the Pill, were no more likely to be depressed than other women in a new U.S. study.

In fact, the women in their 20s and 30s on hormonal contraceptives had fewer symptoms of depression than their peers using other types of contraception or no contraception at all, researchers found.

"This counters somewhat some of the prevailing wisdom that hormone contraceptive use in general is associated with adverse mental health outcomes in women," lead author of the study Dr. Katherine Keyes of the Mailman School of Public Health at Columbia University in New York said.

"When you look at it on a national scale, certainly there's no evidence that at a population level hormonal contraceptive use is associated with an increased risk of mood problems," Keyes added.

Still, Keyes and her colleagues caution, it's also true that depressed women are less likely to use hormone-based contraceptives.

Scientists have suspected that estrogen and progesterone levels play a role in mood disturbances, but studies looking at the effects of hormonal contraception on mood have had mixed results, Keyes and her team note in their report, published in the American Journal of Epidemiology.

To investigate, they looked at data on 6,654 sexually active women between 25 and 34 years old who participated in four surveys between 1994 and 2008.

Contraceptive methods used by women in the group included hormone-based pills, patches, vaginal rings or implants. Non-hormonal methods included IUDs and barriers like diaphragms and condoms.

The women who used hormonal contraceptives were younger, less likely to have children, less likely to smoke, and more likely to have graduated from college, to engage in individual sports like running and in healthy behaviors like getting regular dental and medical checkups.

After adjusting for those differences, the researchers found that women using hormonal contraceptives were less likely to report symptoms of depression in the week preceding the survey.

They were also 32 percent less likely than the other women to have high levels of depressive symptoms and 63 percent less likely to report having attempted suicide in the past year.

Hormonal contraception could improve women's mood by helping to even out menstrual cycle mood swings, Keyes said. "We're definitely following this up and hoping to get at the mechanism," she said.

About 30 percent of women do experience emotional and sexual side effects while using hormonal contraception, Dr. Ellen Wiebe, the medical director of the Willow Women's Clinic in Vancouver, British Columbia, said.

A major problem with the new study, said Wiebe, who wrote an accompanying commentary, is that the hormonal contraceptive users really are a different group from non-users. The "non-users" group also likely includes many women who quit taking hormonal contraception due to mood and sexual side effects.

In their paper, Keyes and her team point out that women with a history of depression are less likely to start taking hormonal contraception, and less likely to stay on it, which could help explain why the risk of depressive symptoms was lower in women who were taking hormonal birth control.

Wiebe also questioned the way depressive symptoms and sexual problems were identified. "A screen for clinical depression does not capture the actual problems that we see with the mood side effects with hormonal contraception, and the same thing with the sexual side effects," she said.

Sexual side effects include having fewer sexual thoughts and lower arousability, Wiebe said, while mood problems typically include irritability.

Given how widely hormonal contraceptives are used in the U.S. and worldwide, "systematic investigation" of the role of outside hormones in mood is warranted, Keyes and her team write. So is study of how mood issues predict who will stick with prescribed hormonal contraception, they conclude.

Decisions on what type of contraception to use and how birth control choices might affect mental health are critical issues for young women, yet there has been very little research into "this intersection of family planning and psychiatric disorders," Keyes said.