I take metoprolol to control a ventricular tachycardia (50mg 2x/day). I feel extremely fatigued, diarreah, abdominal pain, disturbed sleep, racing heart. I have been on it for nearly a year but my dose was doubled from 50 to 100 last month. The side effects seem to have gotten worse in the last 2 weeks. Does anyone know if it builds up in the system? and how long it takes to reach "therapeutic levels"?