Patients with acute psychosis are often physically exhausted due to severe psychotic excitement, incessant wandering, delusions of poisoning, or stupor. In such conditions, the most important etiology of exhaustion may be excessive sympathetic activity. Physical agitation and psychological distress increase the circulation of epinephrine, which induces three physiological changes. First, muscle enzyme synthesis is increased, and enzymes in the cytoplasmic compartment, such as creatine phosphokinese (CPK) and lactate dehydrogenase, are readily soluble. Marked serum CPK elevation of more than 1000 IU/L is common. Second, increased circulation of epinephrine causes a decrease in plasma potassium levels. A significant correlation between serum potassium concentrations and acute agitation symptoms has been described along with the observation that sedation improves acute agitation-induced hypokalemia. In addition, prolongation of the QT interval has been described in psychiatric emergency patients, with a negative correlation noted between serum potassium concentrations and QT interval. Third, epinephrine-induced neutrophilic reactions and glucocorticoids-induced acute neutrophilia cause a slight but significant elevation of white blood cell levels. In addition to excessive sympathetic activity, dehydration may occur. These under-recognized findings in psychiatric emergency patients may be clinically important in preventing comorbid medical disorders that occur secondary to treatment for acute psychosis. © 2008 Bentham Science Publishers Ltd.