Women who used certain forms of birth control may be at a higher risk of developing a brain tumour, a new study out of Denmark suggests.
However, the overall risk remains “extremely rare,” experts say, and the risk generally goes away within several years of stopping the medication.
The use of contraceptive progestogens, including both oral and injectable medication as well as intrauterine devices (IUDs), was associated with an increased risk of meningioma, a study published Thursday in the Journal of the American Medical Association found.
The study was conducted from Jan. 1, 2000, to Dec. 31, 2024, and used Danish nationwide data from roughly three million women between the ages of 15 and 59.
Progestogens are hormones naturally produced in the human body that play an important role in menstruation and pregnancy, and which are also used in synthetic forms in some kinds of contraceptives.
“Several progestogen-containing contraceptives were associated with an increased risk of meningioma. The risk estimates were highest for medroxyprogesterone injections,” the study findings say.
Women taking the injectable medroxyprogesterone were four times more likely than non-users to develop meningioma, while the use of IUDs with low-dose levonorgestrel had the lowest odds (1.14) of increased risk among the eight medications.
Patients who used these medications in the past year were at the highest risk, according to the study.
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“I see many patients with meningiomas in my practice and we’ve always sort of known about this association with progesterone exposure and potential meningioma growth,” said Dr. Derek Tsang, an oncologist at the Princess Margaret Cancer Centre.
Exposure to progestogens can cause pre-existing meningioma to grow, he added.
“If the patient is exposed to progestogen and if it touches the meningioma, it binds to this receptor and that can be potentially what makes it grow,” he said.
Since progestogens are also naturally produced in women’s bodies, it makes women more susceptible to meningioma than men, Tsang said.
But experts say it is important not to panic, and to consider the full scope of the risks and benefits.
The chances of developing meningioma are low, experts say.
“It is important to state that meningioma remains a rare condition (affecting about one in ten thousand people) so that study should not put women off using progestogens, which are effective hormonal treatments for debilitating conditions and suit many women who require contraception,” Dr. Melanie Davies, professor of reproductive medicine at University College London and consultant gynecologist at University College London Hospitals, said in a statement.
If the risks are not properly communicated, “too many women will discontinue the appropriate use of these very effective medications for many debilitating conditions,” said Dr. Nicholas Leyland, president of the Society of Obstetricians and Gynaecologists of Canada.
“To put it in perspective, the chance of dying while driving on our roads is about one in 20,000. But that doesn’t stop us from getting into our car and driving around. That’s what we call an acceptable risk because it’s extremely rare.”
He added that not only is meningioma “extremely rare,” but it is also relatively “benign.”
“The chance of dying from a meningioma is less than one in 500,000 for the women who get it.”
For many women, these contraception methods are an effective tool in the prevention of unintended pregnancy, reduced ovarian and endometrial cancer risk, and the management of heavy or painful periods associated with endometriosis, he said.
“These are great tools for providers to be able to give to women with appropriate counselling to manage abnormal uterine bleeding or the pain of endometriosis,” he said.
The study does not mean that progestogen is carcinogenic, but rather that it is a risk factor, Tsang added.
“There are many, many women who have very good reasons for being on hormone therapy or birth control. And those I would suggest that they would speak should speak with their doctors and weigh the risks and benefits,” Tsang said.
“Much as eating a high-fat diet, heavy in red meat, is a risk factor for developing colorectal cancer, much as going out too much in the sun is a risk factor for skin cancer, exposure to progestogens is a factor for developing meningioma.”
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