The leaflet inside a packet of contraceptive pills lists side effects women might experience, including breast pain, migraines or headaches, stomach problems, and acne. It also says you might experience changes in mood, and depression.

For years women have been telling anecdotes, such as this story in The Debrief, about how they feel their personalities changed after going on the pill. Some of them experience serious mental health problems, which they believe is directly caused by taking hormonal contraception.

The scientific evidence was shaky until 2016 when a massive study of over one million people in Denmark found that women taking the combined pill, which contains oestrogen and progestin (progesterone), were 23 percent more likely to be diagnosed with depression than women who didn't take any pills.

Those on progestin-only pills, also called the mini pill, were 34 percent more likely to be diagnosed with depression.

Women who had suffered from mental health problems, such as Holly Grigg-Spall in The Guardian, felt like their worries about the pill had been validated. There was finally scientific research that backed up what a large proportion of women had been saying all along.

However, as the NHS states on its website, this type of study can provide possible explanations for the use of contraception and the increase in depression, but it cannot say outright that one causes the other.

Due to the inability of scientific studies to cover every possible variable, all the researchers can conclude is that it is possible.

A new study, published in the journal Contraception, complicates things even further. It is an analysis of 26 studies over 30 years of research, and the conclusion is that progestin pills aren't linked to women developing depression at any age.

"Depression is a concern for a lot of women when they're starting hormonal contraception, particularly when they're using specific types that have progesterone," said Brett Worly, an obstetrician-gynecologist at Ohio State Wexner Medical Center and lead author of the study, in a statement.

"Based on our findings, this side effect shouldn't be a concern for most women, and they should feel comfortable knowing they're making a safe choice."

Even for women at high risk, such as those already diagnosed with depression, there was no evidence being on progestin pills made them worse.

"Adolescents and pregnant mums will sometimes have a higher risk of depression, not necessarily because of the medicine they're taking, but because they have that risk to start with," Worly said.

"For those patients, it's important that they have a good relationship with their health care provider so they can get the appropriate screening done – regardless of the medications they're on."

The new study looked at large areas and included women with varying access to healthcare. The researchers believe this makes their findings more widely reliable than the Danish study.

However, none of the papers in the review were randomly controlled trials – meaning participants probably knew what they were taking. This can cause biases and women reporting incorrect symptoms, particularly if they had read a lot about hormonal contraception before.

There were a few papers in the review that found a link between progestin and depression, but the evidence wasn't strong enough to influence the final conclusion.

Worly admits this shouldn't be the end of the conversation on contraception. He said patients have valid concerns about their mental health, and they should continue to talk to their doctors about the best option for them.

Ultimately, the aim of the research was to put women's minds at ease, and to say that progestin pills are an effective and safe form of contraception for many people – so keep using them.

"We live in a media-savvy age where if one or a few people have severe side effects, all of a sudden, that gets amplified to every single person," Worly said.

"The biggest misconception is that birth control leads to depression. For most patients that's just not the case."

This article was originally published by Business Insider.

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