Multaq (dronedarone) is not a blood thinner. It is an antiarrhythmic medication, meaning its job is to help keep your heart in a normal rhythm. Blood thinners (anticoagulants) and Multaq treat different aspects of atrial fibrillation, and many people with AFib take both drugs at the same time, which is likely where the confusion comes from.
What Multaq Actually Does
Multaq works by affecting the electrical signals in your heart to reduce episodes of atrial fibrillation and atrial flutter, two conditions where the upper chambers of the heart beat irregularly. It’s classified as an antiarrhythmic drug with properties spanning all four major categories of heart rhythm medications, though scientists aren’t entirely sure which of those properties matter most for its clinical effect.
The goal of Multaq is rhythm control: keeping your heart beating in a steady, normal pattern. Blood thinners, by contrast, work in the bloodstream itself to prevent clots from forming. When your heart beats irregularly, blood can pool in the upper chambers and form clots that travel to the brain, causing a stroke. That’s why AFib patients typically need both types of medication: one to control the rhythm and one to prevent clots.
Why People Take Multaq With a Blood Thinner
If you have atrial fibrillation, your doctor has likely prescribed a blood thinner alongside Multaq. This is standard practice because even though Multaq reduces AFib episodes, it doesn’t eliminate stroke risk on its own. Earlier studies of antiarrhythmic drugs found that reducing AFib recurrence did not translate into fewer strokes. One large trial (ATHENA) did show a stroke reduction with Multaq specifically, but researchers noted this could have been related to its effects on heart rate and blood pressure rather than rhythm control alone.
The bottom line: Multaq controls your heart rhythm, but you still need a separate blood thinner to protect against stroke.
How Multaq Interacts With Blood Thinners
This is an important practical detail. Multaq can increase the levels of several common blood thinners in your body by interfering with the way your system processes those drugs. It blocks a protein called P-glycoprotein that helps transport medications through your body, and it also slows down certain liver enzymes involved in breaking drugs down.
For the blood thinner dabigatran (Pradaxa), this interaction is significant enough that the 2023 guidelines from the American College of Cardiology and American Heart Association recommend a specific dose reduction for patients with reduced kidney function who also take Multaq. Patients with very poor kidney function should avoid taking dabigatran with Multaq altogether.
Multaq also raises blood levels of rivaroxaban (Xarelto) by roughly 30% and apixaban (Eliquis) by 33% to 46%. Research using pharmacological modeling found that these increases could raise major bleeding risk, with apixaban seeing a 1.5 to nearly 2-fold increase in bleeding risk when combined with Multaq. Reduced doses of these blood thinners may be recommended when taken alongside Multaq. Warfarin levels can also be affected. Your prescriber should be aware of all of these interactions and adjust doses accordingly.
Common Side Effects of Multaq
The most frequent side effects are gastrointestinal. In clinical trials involving over 3,000 patients, diarrhea occurred in 9% of people taking Multaq compared to 6% on placebo. Nausea affected 5% versus 3%, and abdominal pain occurred in 4% versus 3%. Fatigue and general weakness were reported by 7% of patients taking Multaq. Skin reactions including rashes, itching, and eczema appeared in about 5%, and a slowed heart rate (bradycardia) occurred in 3%.
About 12% of patients in clinical trials stopped taking Multaq due to side effects, most commonly because of digestive problems or a heart rhythm change called QT prolongation.
Who Should Not Take Multaq
Multaq carries a boxed warning, the FDA’s most serious safety label, regarding heart failure. In a clinical trial of patients with moderate to severe heart failure (the ANDROMEDA study), those taking Multaq had more than double the mortality rate compared to placebo: 8.1% versus 3.8%. The trial was stopped early because of this finding. Deaths were primarily caused by worsening heart failure.
A separate trial called PALLAS tested Multaq in patients with permanent atrial fibrillation and was also stopped early due to increased rates of death, stroke, and heart failure hospitalization in the Multaq group. Because of these results, Multaq is specifically approved only for patients with episodes of AFib or atrial flutter who return to normal rhythm, not for people whose AFib is permanent. It is also contraindicated in patients with severe heart failure or those recently hospitalized for worsening heart failure symptoms.
If you develop new shortness of breath, swelling in your legs, or unexplained weight gain while taking Multaq, these could be signs of heart failure and should be evaluated promptly.