Common side effects include nausea, abdominal pain, and constipation. It should not be used in those with an already slow heart rate and most of those with heart failure. Quickly stopping the medication in those with coronary artery disease may worsen symptoms. It may worsen the symptoms of asthma. Greater care is recommended in those with liver or kidney problems. Propranolol may possibly cause harmful effects in the baby if taken during pregnancy. Its use during breastfeeding is likely okay but the baby should be monitored for side effects. It is a nonselective beta blocker which works by blocking β-adrenergic receptors.