Recent research finds that an injectable, long-acting contraceptive, commonly known as “the shot,” is associated with a common health risk—a brain tumor called meningioma.

Dr. Varun Kshettry, Associate Professor of Neurological Surgery at Case Western University, and not involved in the study, told The Epoch Times that meningioma is the “most common” type of brain tumor.

Meningiomas are usually benign brain tumors and only 1-4 percent will become cancerous.

Depot medroxyprogesterone acetate, a birth control injection used by millions of American women and sold under the brand name Depo-Provera, has been linked to an almost fourfold risk of a common brain tumor, with the highest risk for long-term users over 30, according to a recent analysis of more than 10 million women.

The findings come as the shot’s manufacturer, Pfizer, battles more than 500 lawsuits claiming that the injectable contraceptive causes brain tumors. Attorneys have argued that the company ignored decades of scientific evidence about tumor risks.

Nearly 4 Times the Tumor Risk

The study, published in JAMA Neurology, found that users of depot medroxyprogesterone acetate had a 2.43 times greater overall risk of developing meningioma than non-users. The risk spiked even higher for women who began use of the contraceptive after age 30, reaching a 3.77 times greater likelihood for those ages 31 to 40.

The research analyzed data from almost 89,000 Depo-Provera users compared with women using other contraceptive methods. Using propensity score matching, researchers were able to isolate the effect of the hormone treatment from other factors that may also increase a woman’s risk of meningioma.

Around 60 percent of meningioma cases among Depo-Provera users could be attributed to the contraceptive, the researchers concluded.

Older women who used Depo-Provera for more than six years faced 3.9 times the normal risk of developing meningioma, while women starting treatment in their 30s consistently showed the highest tumor rates across all categories.

Researchers calculated that there would be about one case of meningioma for every 1,150 women who use Depo-Provera.

While most meningiomas are benign, they can cause significant clinical issues depending on their size and location, especially if they exert pressure on surrounding brain tissue, Dr. Luke Barr, a board-certified neurologist and chief medical officer of SensIQ who was not involved in the study, told The Epoch Times.

Meningioma is the most common type of primary brain tumor, typically arising from the meninges—the protective membranes covering the brain and spinal cord.

Symptoms of a meningioma typically develop gradually and can be difficult to detect at first. They often vary based on the tumor’s location in the brain or, more rarely, the spine, and may include headaches, seizures, or vision changes.

Other known risk factors that increase meningioma risk include exposure to radiation, being older, being female, and using contraceptives.

In October 1992, the Food and Drug Administration (FDA) officially approved Depo-Provera for contraceptive use. However, the U.S. Agency for International Development had been distributing the contraceptive through its family planning initiatives in developing countries for many years prior. Since 1969, Depo-Provera has also been accessible in the United States for noncontraceptive purposes, including treatment of endometrial cancer.

How Depo-Provera May Trigger Tumors

Scientists believe the link stems from meningioma cells’ sensitivity to hormones. Depot medroxyprogesterone acetate is a synthetic form of progesterone, a natural hormone involved in regulating the menstrual cycle.

More than 70 percent of meningiomas have sites on their cells, called progesterone receptors, that respond to progesterone. About 10 percent have similar receptors for estrogen, suggesting that the hormone treatment might stimulate tumor growth, the researchers noted.

While the overall increase in risk is low, the findings are significant because they suggest a potential side effect of a widely used medication. “Although observational studies can’t prove causation outright, there’s strong biological plausibility,” Barr said.

The JAMA study builds on earlier research, including a 2024 study published in the BMJ that found women using depot medroxyprogesterone acetate (Depo-Provera) for just one year faced approximately five times the normal meningioma risk.

“Unfortunately, at this point in time, we do not know the clear reasons why depot medroxyprogesterone carries an increased risk of meningioma formation, as opposed to other contraceptives,” Kshettry said.

There are two potential contributing factors that may explain the increased risk, he added

First is the potency of the progesterone component, and second is that it is delivered systemically throughout the blood. “Beyond this, further research is necessary to elucidate mechanisms further,” he explained.

Depo-Provera already comes with a black box warning from the FDA stating that the contraceptive injection should not be used as a long-term method—longer than two years—unless other contraceptive methods are considered inadequate. This is because women who use Depo-Provera may lose significant bone density.

Lawsuit Underway in Florida

Last month, Pfizer urged a Florida judge to dismiss lawsuits claiming its birth control shot causes brain tumors, arguing that regulators prevented it from including a warning about these tumors on the drug’s label.

Pfizer argued that legal claims that the company failed to warn consumers and doctors about the risk are blocked because the FDA previously rejected such warnings before the lawsuits began.

However, lawyers for the women suing Pfizer said the company ignored scientific evidence dating back to the 1980s that suggested Depo-Provera could cause these brain tumors. One study published in 1983 showed that progestin, an ingredient in Depo-Provera, can bind to meningiomas.

The outcomes of the lawsuit may affect more than 500 other cases involved in ongoing litigation, court records show.

What This Means for Current Users

Experts emphasize that while the increased risk is statistically significant, meningioma remains relatively rare overall.

The drug is a reliable and effective form of contraception for many women, Barr said. However, patients and providers should be aware of this emerging risk, especially in those with other risk factors or a personal or family history of meningioma, he added.

The study authors recommend that health care providers carefully consider these risks when prescribing the contraceptive, particularly for women over 30 or those planning extended use.

Pfizer did not respond to a request for comment.

Update: This article has been corrected to say that meningiomas are brain tumors and usually not brain cancers. The Epoch Times regrets this error.