An individual patient is always advised to consult their own physician. My problems began while taking Claritan-D for sinus congestion. It has continued for over a month after I have stopped taking the Claritan and I can't seem to stop the Toprol without it racing again. Antihistamines are notorious for causing irregular heart beats in some patients. If you have irregularities, you should avoid all antihistamines, caffeine, etc.
Beta blockers seem very safe with pregnancy.
As of yesterday I am using Toprol XL 50mg. I am extremely tired, but I am not sure if this is from Toprol or from being in the hospital 3 days ago with a heart rate of 210 bpm. Most patients will experience fatigue with beta blockers. The pulse slowing is individual and the dosage would need to be increased until the pulse is slow enough. This may cause further fatigue.