Mirena looks like a little T and is small enough to easily fit in the palm of your hand.

Made of plastic, the device releases an artificial hormone that prevents conception after placement in the uterus. While effective, the device can be dangerous, according to thousands of women across the country who filed lawsuits against the manufacturer, Bayer Pharmaceuticals.

The company is accused of selling a dangerous product, engaging in deceptive advertising and concealing the risk of complications. The devices can poke into organs, move around and cause a pressure buildup in the skull.

Injured women are seeking compensation for medical expenses, lost wages and pain and suffering.

Women say Mirena’s label didn’t warn them about serious complications. They want Bayer punished, saying the company knowingly harmed them.

Many of the lawsuits have been grouped together into a consolidated federal case in New York or a multicounty case in New Jersey. A third federal group may be formed. They make similar claims against Bayer.

In April 2013, a number of Mirena lawsuits that claimed device migration, organ perforation and related injuries were consolidated into what’s called multidistrict litigation. The cases were grouped together in the Southern District of New York under U.S. District Judge Cathy Seibel. It included 1,800 cases.

Bayer noted the product contained a warning: “Perforation or penetration of the uterine wall or cervix may occur during insertion although the perforation may not be detected until some time later.” The lawsuits argued that Mirena could perforate the uterus at any time — even without injury at insertion. Lawsuits called this “secondary perforation,” “spontaneous perforation” or “spontaneous migration.” They alleged Bayer’s label used from 2008 through 2014 did not contain warnings for secondary perforation.

In 2016, Seibel excluded all “secondary perforation” experts for the women suing Bayer. The judge said they were not qualified to testify. About 1,300 cases were pending at the time, and Seibel granted Bayer’s request for dismissal. The women appealed, but the appeals court has yet to make a decision.

The majority of existing litigation centers on organ perforation and device migration. But a new group of Mirena lawsuits emerged claiming Mirena caused pseudotumor cerebri (meaning “false brain tumor”), also known as intracranial hypertension. This condition is the result of an abnormal elevation of cerebrospinal fluid in the skull causing neurological complications, including symptoms of headache and vision problems.

The panel responsible for deciding whether to consolidate similar lawsuits previously denied a motion in July 2014, to consolidate the cases alleging “pressure on the brain.” The panel determined its ruling based on the limited number of actions pending at the time and case-specific cause of symptoms leading to diagnosis.

In February 2017, plaintiffs filed a second motion to centralize the lawsuits. In that motion, the plaintiffs argued that the litigation had expanded dramatically over the two-year time period. While the panel noted that it rarely reaches a different conclusion once an earlier denial has occurred, it will do so where a significant change in circumstances is realized. In reaching its decision in April 2017, the panel found that there had been such a change.

The number of lawsuits pending against Mirena’s manufacturer, Bayer, regarding intracranial hypertension had increased from just nine actions pending in six different districts to 113 pending actions in 17 districts. Additionally, causation for the plaintiffs’ condition now largely pointed to a hormonal component of Mirena and whether it is capable of leading to plaintiffs’ injuries.

Currently, just over 220 consolidated cases are pending before Judge Paul A. Engelmayer, whom the panel referred to as an “experienced transferee judge with the willingness and ability to manage [the] litigation,” at the Southern District of New York.

In 2013, the Supreme Court consolidated other cases in multicounty litigation in New Jersey under Judge Brian R. Martinotti. Then, in 2016, the court reassigned those cases to Judge Rachelle L. Harz.

“The complaints filed allege that the plaintiffs suffered injuries and/or damages as a result of misplacement of the Mirena device,” the New Jersey Judiciary Court System says online.

Plaintiffs in New Jersey had similar complaints to those in New York. Cases in New Jersey are in the middle of discovery — the phase of litigation where plaintiffs and defendants are providing each other with requested information. This may include internal documents and medical testimony.