I am taking bethanechol chloride for my bladder. Does this drug have any side effect?

Yes. All drugs, even aspirin, have potential side effects. Serious reactions that can occur with Bethanechol include: asthma, low blood pressure, rapid heart rate and seizures . Less serious but more common side effects include: abdominal pain or cramping, nausea, belching, diarrhea, need to urinate, excess saliva, headache, fatigue, flushing, sweating, and eyes tearing.