• Uncontrolled hypertension
• Cardiac arrhythmias: Ventricular tachycardia or fibrillation
• Myocardial ischemia
• Ephedrine-resistant hypotension with neuraxial blockade: A direct-acting drug should be used
• Acute use may increase the MAC of volatile drugs
• Chronic use may decrease the dosage of anesthetic drugs
• The patient may exhibit increased sensitivity to the arrhythmogenic effects of volatile drugs

MAC = minimum alveolar concentration.