Propranolol withdrawal and thyroid hormones in patients with essential hypertension

The effect of abrupt withdrawal of propranolol on serum concentrations of triiodothyronine (T 3 ) and thyroxine (T 4 ) was investigated in 5 patients with uncomplicated essential hypertension. The patients had been treated from 2 to 18 mo before the study was begun. Doses varied from 160 to 480 mg propranolol daily. Four of the patients studied developed tachycardia, sweating, or tremor within 2 to 6 days after withdrawal of propranolol. In 1 patient reversible ischemic ECG changes were recorded. The serum concentrations of free T 3 increased in the 4 patients suffering from withdrawal symptoms. The mean increase on the day the symptoms started was 51% (range, 22 to 74, 2 p = 0.01). This increase in serum‐free T 3 correlated positively with the serum propranolol concentration on the last day propranolol was given (r = 0.91, 2 p = 0.03). In the one patient, who did not develop withdrawal symptoms, the serum concentration of propranolol was very low, and the free T 3 level remained unchanged. No significant changes in serum concentrations of free T 4 or total thyroid hormones were found in any of the patients. We suggest that the propranolol withdrawal symptoms are, at least partially, caused by an increase in the thyroid hormone, T 3 .