Acute effect of atenolol on serum thyroid hormones in hyperthyroid patients

The effect of atenolol on serum thyroid hormones levels is controversial. To get more information on this problem we studied the effect of propranolol and atenolol on plasma thyroid hormone concentrations in 20 thyrotoxic patients. Propranolol but not atenolol caused a significant decrease in T3 levels whereas no significant changes wee observed in T4 levels after both propranolol and atenolol administration.