Users of the relatively new blood-thinner Pradaxa (dabigatran) are at an increased risk of major gastrointestinal bleeding episodes compared to patients who take the decades-old blood-thinner warfarin (Coumadin, Jantoven and generics), according to the results of a recent U.S. Food and Drug Administration (FDA) study of more than 134,000 Medicare patients ages 65 and older.

The study looked at the risk of ischemic or clot-related stroke, bleeding in the brain, major gastrointestinal (GI) bleeding, heart attack, and death. Both Pradaxa and warfarin are used to reduce the risk of stroke and blood clots in patients with a common type of abnormal heart rhythm called non-valvular atrial fibrillation (AF).

While Pradaxa had lower rates of clot-related strokes, bleeding in the brain, and death, the study found that the medication presented an increased risk of major gastrointestinal bleeding, compared to warfarin. The heart attack risk was similar for the two drugs, according to the FDA study, published in May 2014.

In 2014, Pradaxa manufacturer Boehringer Ingelheim agreed to pay $650 million to settle some 4,000 Pradaxa lawsuits alleging that the anticoagulant causes excessive and uncontrollable bleeding.

The announcement did not stem the flow of Pradaxa lawsuits over the blood-thinner’s lack of a bleeding antidote. Patients accuse the drug makers of manufacturing and selling a dangerous drug while failing to warn users or the medical community that a reversal agent does not exist.

Boehringer Ingelheim is reportedly close to finding an antidote to Pradaxa and is trying to expedite the FDA approval process.

A federal judicial panel has established a multidistrict litigation to handle all the Pradaxa lawsuits.

Pradaxa received FDA approval in 2010. Boehringer Ingelheim spent $464 million in 2011 to promote the drug and by 2012, Pradaxa sales had eclipsed $1 billion. But lawsuits quickly began cropping up.

The year after hitting the market, the drug came under attack by physicians groups and patient advocates, USA Today reported, concerned about the 3,781 adverse effects and 542 deaths reported to the FDA.

In 2011, according to the newspaper, Pradaxa complications led all other medications in the number of deaths reported to the FDA, and a January 2012 Cleveland Clinic study showed Pradaxa patients may be at an increased risk of heart attack and irreversible bleeding complications.

“It’s a drug of questionable efficacy, and the real fraud has been perpetuated on the patients,” a plaintiff’s attorney told USA Today. “They developed a take-and-and-forget-it, one-size-fits-all drug, which injured an extreme amount of people.”

Pradaxa joins the new generation of blood-thinners that includes Eliquis (apixaban) and Xarelto (rivaroxaban), which are also accused of causing irreversible internal bleeding episodes that can result in death.

The drugs are marketed as the first alternative to warfarin (Coumadin), which has been on the market in the United States since the 1950s.

Warfarin users are able to reverse a bleeding event with a dose of vitamin K and fresh frozen plasma to reverse the drug’s anticoagulant effects.