Myrbetriq (mirabegron) is not an anticholinergic. It belongs to a completely different drug class called beta-3 adrenergic agonists, and it works through a separate mechanism in the bladder. This distinction matters because anticholinergic medications carry a well-documented set of side effects, particularly for older adults, that mirabegron largely avoids.
How Myrbetriq Works
Myrbetriq relaxes the bladder muscle by activating beta-3 adrenergic receptors, the same type of receptor that responds to your body’s sympathetic nervous system. When these receptors are stimulated, the bladder muscle loosens, allowing it to hold more urine and reducing the sudden urgency that defines overactive bladder (OAB).
Anticholinergic OAB drugs, such as oxybutynin, tolterodine, and solifenacin, take a different approach. They block muscarinic receptors, which are the receptors that trigger the bladder muscle to contract. The problem is that muscarinic receptors exist throughout the body, including in the brain, salivary glands, and gut. Blocking them produces a predictable pattern of side effects: dry mouth, constipation, blurred vision, and in some cases cognitive impairment. Because Myrbetriq doesn’t touch these receptors, it doesn’t carry what pharmacists call “anticholinergic burden.”
Why the Distinction Matters
Anticholinergic side effects aren’t just uncomfortable. In older adults, cumulative anticholinergic exposure has been linked to delirium, confusion, cognitive decline, falls, and fractures. Pharmacists track this exposure using tools like the Anticholinergic Cognitive Burden (ACB) scale, which scores drugs from 1 (mild anticholinergic activity) to 3 (strong anticholinergic effects). Traditional OAB medications typically score high on this scale. Mirabegron does not appear on it because it is not an anticholinergic.
For anyone already taking other medications with anticholinergic properties (certain antidepressants, antihistamines, or sleep aids), adding yet another anticholinergic for bladder symptoms can push the total burden into a range associated with real cognitive risk. Mirabegron offers a way to treat OAB without stacking that burden higher.
Side Effect Differences in Practice
Clinical comparisons back up the pharmacology. In head-to-head analyses, every anticholinergic OAB drug produced significantly more dry mouth than mirabegron at its standard 50 mg dose. Several anticholinergics also caused significantly more constipation. When mirabegron was compared directly to placebo, there was no statistically significant difference in the rates of dry mouth, constipation, or blurred vision.
In a network meta-analysis published in Drugs & Aging, anticholinergic OAB medications increased the odds of dry mouth by roughly 4 to 8 times compared with placebo, and constipation by about 2 to 5 times. Mirabegron showed no meaningful increase in either.
Mirabegron does have its own side effect profile, though. It can raise blood pressure, and it is contraindicated in people with severe uncontrolled hypertension (systolic 180 or above, diastolic 110 or above). Blood pressure should be checked before starting the medication and monitored periodically while taking it, especially if you already have high blood pressure.
Cognitive Effects in Older Adults
A phase 4 clinical trial called PILLAR specifically tested whether mirabegron affected cognitive function in patients aged 65 and older. Nearly 900 patients were randomized to mirabegron or placebo, and about 27% of participants in each group already had some degree of cognitive impairment at the start. After 12 weeks, cognitive scores changed by the same negligible amount in both groups (a 0.2-point decline with mirabegron versus 0.1-point decline with placebo, neither statistically significant). The study concluded that mirabegron did not contribute to drug-related cognitive side effects in this population.
This is a meaningful contrast with anticholinergic OAB drugs, where cognitive concerns are one of the primary reasons clinicians look for alternatives, particularly in older patients.
Where Myrbetriq Fits in OAB Treatment
The American Urological Association’s 2024 guidelines list both anticholinergic medications and beta-3 agonists like mirabegron as options for OAB, with a strong recommendation and the highest evidence grade for both. Notably, the updated guideline moves away from a rigid step-therapy approach. Rather than requiring patients to try anticholinergics first and fail before moving to mirabegron, the guideline emphasizes shared decision-making based on a patient’s needs, preferences, and tolerance for side effects.
For people who want to avoid anticholinergic side effects, or who are already on other medications that contribute to anticholinergic burden, mirabegron can be a reasonable first choice rather than a backup plan.
Combining Myrbetriq With an Anticholinergic
Because mirabegron and anticholinergics work through different receptors, they can sometimes be used together when a single medication isn’t enough. A phase 2 trial tested various dose combinations of mirabegron and solifenacin (an anticholinergic) in over 1,300 patients. The combinations significantly improved bladder capacity, reduced urination frequency, and decreased urgency episodes compared with solifenacin alone. The combinations were generally well tolerated, though constipation rates were slightly higher than with either drug by itself.
If your current OAB medication isn’t providing adequate relief, combination therapy is something to discuss with your prescriber. It’s worth noting that adding an anticholinergic back into the picture reintroduces those anticholinergic side effects, so the decision involves weighing symptom control against tolerability.