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• Posted March 3, 2026

A-Fib Drug Could Interact With Blood Thinners, Increase Risk Of Dangerous Bleeding

People with abnormal heart rhythms could be at risk of dangerous bleeding from a serious combination of prescription medications, a new study says.

Patients with atrial fibrillation (A-Fib) often are prescribed diltiazem to help control their heart rate, researchers said in the Annals of Internal Medicine.

Because A-Fib also greatly increases a person’s risk of stroke, these patients also are prescribed blood thinners like apixaban or rivaroxaban, researchers said.

But the combination of diltiazem with either of those blood thinners caused higher rate of serious bleeding events among a group of 23,000 patients, researchers found.

“Although diltiazem remains an appropriate and effective option for heart rate control in selected patients, our results underscore that bleeding risk must be a central consideration in treatment decisions,” lead researcher Ghadeer Dawwas said in a news release. She’s an assistant professor of medicine and health policy at Vanderbilt University Medical Center in Nashville, Tennessee.

Diltiazem is a calcium channel blocker, which helps slow heart rate in people with A-Fib and weaken the heart’s contraction, according to the American Heart Association.

However, diltiazem also inhibits the function of cytochrome enzymes, which are crucial for the metabolism of drugs. This might cause blood thinners to become more concentrated in the bloodstream, increasing the risk of dangerous bleeding, researchers said.

For this study, researchers compared 23,000 A-Fib patients prescribed diltiazem against another 23,000 prescribed metoprolol, a beta blocker also used to slow the heart rate in these patients. These patients also had been prescribed either apixaban or rivaroxaban.

The team tracked which drug combination caused a higher risk of dangerous bleeding in the brain, GI system or elsewhere in the body.

Results showed 467 serious bleeding events among diltiazem users compared to 397 among those prescribed metoprolol.

Overall, diltiazem was associated with an 18% increased risk of dangerous bleeding, the study found.

Further, the risk grew with higher doses of diltiazem, researchers discovered.

The bleeding risk “is especially relevant for patients receiving higher doses exceeding 120 mg/day of diltiazem or those taking additional interacting medications,” Dawwas said. “In such cases, metoprolol may represent a safer alternative.”

More information

The American Heart Association has more on atrial fibrillation medications.

SOURCE: Vanderbilt University, news release, Feb. 26, 2026