Common side effects of Betmiga (mirabegron) include increased heart rate (tachycardia), urinary tract infections, and increased blood pressure[1][3][5][7]. Other mild side effects can include headache, cold-like symptoms, constipation (especially in children), joint pain, dizziness, and fatigue[7].
Uncommon side effects (may affect up to 1 in 100 people) include bladder infection (cystitis), feeling your heartbeat (palpitations), vaginal infection, indigestion (dyspepsia), infection of the stomach (gastritis), swelling of the joints, vulvovaginal itching (pruritus), mild increase in liver enzymes, itching, various types of rash, and hives (urticaria)[1].
Rare but serious side effects may include irregular heartbeat (atrial fibrillation), very high blood pressure, difficulty urinating, severe swelling of the face, mouth, or throat (angioedema), and bladder pain[1][7]. If you experience symptoms of severe allergic reaction or abnormal heart rhythm, you should stop taking the medication and seek urgent medical advice.