My Husband Has IBS And Was Prescribed Bethanechol For Acid

My husband has IBS and was prescribed bethanechol for acid reflux a couple of years ago. When picking up the prescription this time, the pharmacist asked if he had IBS. She said this medication should not be used if you have IBS. He has been taking it for 2 years. They called his doctor and he said it was ok. Could taking this have caused him to have problems? He has severe issues with IBS and acid reflux still.