Myrbetriq Drug Interactions: What to Avoid and What to Tell Your Doctor

Myrbetriq (mirabegron) has several clinically important drug interactions that every patient and prescriber should know about. The most significant involve mirabegron's role as a moderate inhibitor of a key liver enzyme called CYP2D6 — which affects how the body processes many other common medications. Here's what you need to know before starting Myrbetriq.

Why Myrbetriq Causes Drug Interactions: The CYP2D6 Enzyme

The liver uses enzymes to break down medications so they can be cleared from the body. CYP2D6 is one of the most important of these enzymes, responsible for metabolizing a large number of commonly used drugs. Myrbetriq is a moderate inhibitor of CYP2D6 — meaning it slows down this enzyme.

When CYP2D6 is inhibited, drugs that depend on it for metabolism accumulate at higher levels in the blood than intended. For most drugs, this is a minor concern. But for drugs with a narrow therapeutic index — where even a small increase in blood level can cause toxicity — it becomes clinically significant. When you start Myrbetriq, your doctor should review all your other medications to check for CYP2D6 interactions.

Major Interaction: Ozanimod — Avoid This Combination

Ozanimod (Zeposia), used to treat multiple sclerosis and ulcerative colitis, should not be taken with Myrbetriq. An active metabolite of ozanimod inhibits MAO-B in vitro, and combining it with drugs that increase norepinephrine or serotonin — which includes drugs that inhibit CYP2D6 — can cause a potentially dangerous hypertensive crisis (a sudden, severe rise in blood pressure). This combination should be avoided entirely.

Major Interaction: Metoclopramide Nasal Spray

Metoclopramide intranasal spray (used for acute migraines) is metabolized by CYP2D6, and the nasal spray dosage cannot be adjusted. Concurrent use with strong CYP2D6 inhibitors is not recommended by the FDA. While Myrbetriq is a moderate (not strong) inhibitor, avoid this combination or consult your doctor if both are needed.

Moderate Interactions: CYP2D6 Substrates Requiring Monitoring

These drugs are metabolized by CYP2D6 and may reach higher blood levels when taken with Myrbetriq. Your doctor should monitor you for signs of increased drug effects or side effects:

• Metoprolol (Lopressor, Toprol): A common beta-blocker for high blood pressure and heart conditions. Myrbetriq may increase metoprolol levels, potentially causing excessive slowing of heart rate or blood pressure drop. Monitor heart rate and BP.
• Carvedilol: Another beta-blocker used for heart failure and hypertension. Similar interaction risk as metoprolol — monitor.
• Flecainide (Tambocor) and Propafenone (Rythmol): Antiarrhythmic drugs for heart rhythm problems. Narrow therapeutic index — elevated levels can trigger new arrhythmias. Monitor carefully.
• Thioridazine: An older antipsychotic with a narrow therapeutic index. Myrbetriq can significantly increase thioridazine levels. Caution advised.
• Desipramine and Amitriptyline: Tricyclic antidepressants metabolized by CYP2D6. Elevated levels can cause sedation, dry mouth, and cardiac effects.
• Aripiprazole (Abilify): An antipsychotic metabolized by CYP2D6. Myrbetriq may increase levels — monitor for increased sedation or side effects.
• Atomoxetine (Strattera): A non-stimulant ADHD medication metabolized by CYP2D6. Monitor for increased cardiovascular and CNS effects.

Digoxin: Separate Interaction Mechanism

Digoxin is used for heart failure and atrial fibrillation. It has a very narrow therapeutic index — small changes in blood levels can cause toxicity or ineffectiveness. Myrbetriq interacts with digoxin through a different mechanism (P-glycoprotein transport), and the FDA prescribing information specifically advises:

• When starting Myrbetriq in a patient on digoxin, use the LOWEST dose of digoxin initially
• Monitor serum digoxin concentrations regularly
• Titrate digoxin dose to the desired clinical effect, not just the target range

Blood Thinners (Warfarin)

There have been postmarketing reports of increased INR (blood thinning effect) in patients taking warfarin with mirabegron. While the interaction is considered minor, it's prudent to monitor INR after starting or stopping Myrbetriq if you take warfarin.

What to Tell Your Doctor and Pharmacist

Before starting Myrbetriq, make sure your prescriber knows about ALL medications you take, including:

• All prescription medications — especially heart drugs, antidepressants, antipsychotics, ADHD medications
• Over-the-counter medications — including pain relievers and antihistamines
• Supplements and herbal products
• Blood thinners (warfarin, Eliquis, Xarelto)
• Heart rate and blood pressure medications

Also see Myrbetriq Side Effects and What Is Myrbetriq? for related guides.