I recently became curious about Myrbetriq (Mirabegron) after hearing a presentation where a researcher talked very positively about it. I haven't thought about it very much, although I did notice a few things:

The Mayo Clinic has a webpage up that has a list, under a headline "Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines". The list contained Orgovyx (Relugolix).

A research paper pointed to by the guy who first drew my attention to this drug stated that the drug is indicated for the symptoms of BPH, i.e. overactive bladder (OAB). Perhaps not necessarily OAB due to external beam therapy? The drug was said to have less side effects than whatever is traditionally used, for OAB associated with BPH. The paper examined how good this drug was when used in combination with tamsulosin compared to tamsulosin by itself.

"In conclusion, compared to tamsulosin monotherapy, combination therapy with mirabegron 50 mg and tamsulosin 0.4 mg significantly improves LUTS in patients with BPH, particularly storage symptoms, without increasing adverse events. This combination therapy represents a promising treatment option." https://pubmed.ncbi.nlm.nih.gov/40759594/

More than 10% of patients taking this experience higher blood pressure. The list of side effects that could cause someone to quit in disgust seemed long....