per UWorld question #4126: “Thyroid hormones cause an increase in beta-adrenergic receptor expression, which leads to an increase in sympathetic activity. Beta blockers (eg, propranolol, atenolol) are recommended as initial therapy to control heart rate and hyperadrenergic symptoms. In addition, propranolol decreases conversion of T4 to T3 in peripheral tissues. The beta blocker should be initiated as soon as hyperthyroidism is diagnosed and should be continued until the hyperthyroidism is adequately treated with thionamides, radioiodine, and/or surgery.”