Mirabegron XR Side Effects: What to Expect and When to Call Your Doctor

One of the biggest reasons doctors choose Mirabegron XR (Myrbetriq) over older overactive bladder medications is its favorable side effect profile. Unlike anticholinergic OAB drugs — which cause dry mouth, constipation, and cognitive effects — Mirabegron XR works through a different mechanism and generally causes fewer of these problems. That said, it is not free of side effects. Here is a clear, honest guide to what patients commonly experience and what requires medical attention.

Why Mirabegron XR Has Fewer Side Effects Than Older OAB Drugs

Older OAB medications like oxybutynin and tolterodine work by blocking muscarinic receptors throughout the body — including in the salivary glands (causing dry mouth), the colon (causing constipation), the eyes (causing blurred vision), and the brain (causing memory problems). Mirabegron XR, by contrast, works by activating beta-3 adrenergic receptors specifically in the bladder muscle, causing it to relax and hold more urine. This targeted mechanism is why Mirabegron XR causes fewer systemic anticholinergic effects.

Common Side Effects of Mirabegron XR

In clinical trials with over 4,000 patients, these side effects occurred in more than 2% of patients taking Mirabegron XR and more often than in patients taking placebo:

High blood pressure (hypertension): The most clinically significant common side effect. Mirabegron XR can raise blood pressure, particularly at higher doses. Your doctor will monitor your blood pressure periodically. If you have uncontrolled high blood pressure (systolic ≥180 mmHg or diastolic ≥110 mmHg), mirabegron is not recommended.

Nasopharyngitis (cold-like symptoms): Runny nose, sore throat, or cold symptoms. Usually mild and self-limiting.

Urinary tract infection (UTI): UTI symptoms were slightly more common in mirabegron users than placebo in trials. If you experience burning urination or new fever, report it to your doctor.

Headache: Mild to moderate headache occurs in some patients, especially when starting treatment. Usually resolves with continued use.

When used in combination with the anticholinergic solifenacin (Vesicare), additional common side effects include dry mouth, constipation, and tachycardia (fast heartbeat). These arise from the solifenacin component, not mirabegron itself.

Serious Side Effects: When to Seek Immediate Medical Help

Stop taking Mirabegron XR and seek emergency medical attention immediately if you experience:

Angioedema: Swelling of the face, lips, tongue, throat, or larynx. This is a potentially life-threatening allergic reaction that can block the airway. It can occur after the first dose or after multiple doses. If you have difficulty breathing or upper airway swelling, call 911 immediately.

Severe allergic reaction: Rash, hives, itching, swelling, or difficulty breathing may indicate hypersensitivity.

Important Side Effects to Monitor With Your Doctor

Blood pressure increase: Schedule regular blood pressure checks, especially in the first months of treatment. If your blood pressure rises significantly, contact your provider.

Urinary retention: If you have trouble emptying your bladder completely or notice a very weak urine stream, tell your doctor. This is more likely if you also have bladder outlet obstruction or take antimuscarinic drugs.

Atrial fibrillation: Post-marketing reports have included atrial fibrillation (irregular heartbeat) associated with mirabegron use. If you develop palpitations, chest discomfort, or shortness of breath, seek prompt medical evaluation.

Stevens-Johnson syndrome (extremely rare): A rare but severe skin reaction involving blistering and skin peeling. If you develop a severe rash with blistering, fever, or eye inflammation, stop the medication and seek emergency care.

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Side Effects Mirabegron XR Does NOT Typically Cause

One reason providers prefer Mirabegron XR — especially in older patients — is that it does not cause the anticholinergic effects common with older OAB drugs. Specifically, Mirabegron XR does not typically cause:

Dry mouth

Constipation (when used as monotherapy)

Blurred vision

Memory problems or cognitive decline

Weight gain

Special Populations: Extra Precautions

Patients with high blood pressure: Monitor BP regularly. Not recommended if your BP is severely uncontrolled.

Patients with kidney or liver disease: Dose adjustments may be needed. Not recommended for end-stage renal disease or severe liver impairment.

Pregnant or breastfeeding patients: Discuss risks with your provider. Adequate studies in pregnant humans are not available.

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Summary: Key Side Effects to Know

Most patients tolerate Mirabegron XR well. The side effects to watch most closely are blood pressure elevation (routine monitoring), angioedema (stop immediately and call 911), and urinary retention (especially with other OAB drugs). For information on drug interactions that can compound these risks, see our guide on Mirabegron XR drug interactions.