Gemtesa (vibegron) causes relatively few side effects for most people who take it. In clinical trials lasting 12 weeks, the most common were headache (4%), nasal congestion or sore throat (2.8%), and diarrhea (2.2%). These rates were only slightly higher than what people taking a placebo experienced, which means many of these symptoms may not even be caused by the medication itself. Over longer use, urinary tract infections and high blood pressure become more notable.
Common Side Effects in the First Few Months
In the main 12-week clinical trial used for FDA approval, only three side effects occurred in at least 2% of patients taking Gemtesa and at a higher rate than placebo:
- Headache: 4.0% on Gemtesa vs. 2.4% on placebo
- Nasopharyngitis (cold-like symptoms): 2.8% vs. 1.7%
- Diarrhea: 2.2% vs. 1.1%
These are mild for most people and often resolve on their own as your body adjusts to the medication. The differences between Gemtesa and placebo are small enough that, for any individual, it can be hard to know whether the drug or something else is responsible.
Side Effects With Longer Use
A 52-week extension study paints a fuller picture of what to expect if you stay on Gemtesa. Urinary tract infections were reported in 6.6% of patients, making them the most commonly discussed longer-term concern. Bronchitis showed up in 2.9% of patients. Hypertension appeared in 8.8% of patients over the full year, a number worth paying attention to if you already have blood pressure concerns.
Headache (5.5%), nasopharyngitis (4.8%), and dry mouth (1.8%) also appeared in the long-term data. Despite these numbers, very few people stopped taking the drug because of side effects. Only 1.5% of patients in the extension study discontinued due to adverse events, which was lower than dropout rates seen with older overactive bladder medications like anticholinergics and mirabegron.
Blood Pressure and Heart Rate
Gemtesa works by activating a specific type of receptor on the bladder muscle that helps it relax during filling. Similar receptors exist in blood vessels and the heart, so cardiovascular effects are a reasonable concern. The good news: a dedicated blood pressure study using 24-hour monitoring found essentially no meaningful difference between Gemtesa and placebo. Daytime systolic blood pressure increased by less than 1 mmHg compared to placebo, and there was zero difference in diastolic blood pressure. Heart rate increased by about 1 beat per minute, which is clinically insignificant.
That said, the 8.8% hypertension rate in the long-term study suggests blood pressure can creep up for some people over months of use. This doesn’t necessarily mean the drug caused it, since hypertension is common in the older population that typically takes Gemtesa. Still, periodic blood pressure checks are a reasonable precaution.
Urinary Retention Risk
Urinary retention, where you have difficulty fully emptying your bladder, occurred in fewer than 2% of patients in trials. But it’s the side effect that carries the most practical risk. You’re more likely to experience it if you have a blockage at the bladder outlet (common in men with enlarged prostates) or if you’re also taking an anticholinergic medication for bladder symptoms. If you notice a weak urine stream, a feeling that your bladder isn’t emptying, or increasing difficulty starting urination, that warrants a prompt conversation with your prescriber.
Who Should Not Take Gemtesa
Gemtesa is not recommended for people with end-stage kidney disease (with or without dialysis) or severe liver impairment, because the drug isn’t cleared from the body effectively in those situations. It’s also contraindicated if you’ve had an allergic reaction to vibegron or any inactive ingredient in the tablet. Beyond these groups, there are no broad restrictions, which is part of why Gemtesa has become a popular option for overactive bladder.
How It Compares to Older Bladder Medications
The side effect profile of Gemtesa is notably different from older anticholinergic bladder drugs, which commonly cause dry mouth, constipation, and blurred vision. In the long-term study, dry mouth occurred in only 1.8% of Gemtesa patients. Constipation and blurred vision were rare enough that they didn’t reach reportable thresholds. This is a meaningful distinction if you’ve tried an anticholinergic and couldn’t tolerate it. Fewer people also dropped out of Gemtesa trials due to side effects compared to both anticholinergics and mirabegron, the other drug in its class.