(CNN) An analysis of 30 years of research finds no correlation between progestin-only birth control methods and depression, said Dr. Brett Worly, lead author of the new study and OB-GYN at the Ohio State University Wexner Medical Center.
"A lot of my patients want to know if their birth control will lead to depression," explained Worly. "This one concern sometimes keeps them from choosing a method. Based on our findings, it shouldn't be a concern for most women, and they should feel comfortable knowing they're making a safe choice."
"This is an interesting finding," said Dr. Suzanne Gilberg-Lenz, a Los Angeles OB-GYN who is also board certified in integrative and holistic medicine, who had no involvement in the study.
Gilberg-Lenz says additional data-based research is welcome. "The difficulty I have in clinical practice is that I have so much anecdotal evidence, and patients also arrive with their biases," she said.
Progestin-only methods include the "mini" birth control pill and longer-lasting forms of contraception such as an implant, or a shot of medroxyprogesterone commonly known as Depo-Provera.
Progestin-only methods must be taken at the same time each day, and work by thickening cervical mucus and thinning the lining of the uterus, preventing the sperm from reaching the egg and implanting if it does. These methods also block ovulation, but not reliably.
Progestin-only birth control is often used by women who want a longer-lasting form of contraception or who want to avoid taking estrogen due to a history of blood clots or cancer concerns.
In 2016, Worly and his colleagues published the same type of meta-analysis on combined hormonal birth control, which uses both estrogen and progestin, and works by blocking ovulation. The study found that it, too, had no strong connection to an increased risk for depression.
Worly's research appears to contradict a large study published in 2016 that found an increased risk for depression in Norwegian women taking hormonal birth control compared to women who didn't use contraception.
That study used data from the National Prescription Register and the Psychiatric Central Research Register in Denmark that tracked the health of more than 1 million Danish women between the ages of 15 and 34 over 14 years.
"We have known for decades that women's sex hormones, estrogen and progesterone, have an influence on many women's mood. Therefore, it is not very surprising that also external artificial hormones acting in the same way and on the same centers as the natural hormones might also influence women's mood or even be responsible for depression development," study lead Dr. Øjvind Lidegaard, a professor at the University of Copenhagen in Denmark, told CNN when the study released.
"Our work is different," said Worly. "The study last year was a population health study that observed a relationship between birth control and mood. We didn't look at mood changes and feeling down because those are difficult to measure. We looked specifically at depression."
Worly says his team looked at thousands of studies and rejected those using less scientific methods before analyzing their data.
"We found hormonal contraception to be a safe, effective way to prevent pregnancy that will not cause depression in most women, said Worly.
Worly also says that his research should not be "the end of the discussion."
"We need much more quality research," said Worly. "Some of these papers were amazingly well done, but there was room for improvement among others. We need large randomized controlled trials of the highest scientific value. Those cost lots of resources and money, but we need to get those resources and do those type of studies."
Gilberg-Lenz agrees. "This topic can use some higher quality studies to bolster findings, influence more studies and perhaps have an impact on clinical practice," she said. "Mood disorders are prevalent among women of reproductive age who need as many reliable contraceptive choices as possible."