The effect of propranolol withdrawal on thyroid hormones in normal and hyperthyroid subjects

Blood thyroid hormone levels were measured during, and for 6 days after, treatment with propranolol (160 mg/day, 4-8 weeks) in five hyperthyroid patients and six normal volunteers. In hyperthyroid patients triiodothyronine (T3) and free triiodothyronine index (FT3I) rose to peak levels 60 h after propranolol withdrawal without significant change in thyroxine (T4) or Thyopac-3 test. In normal subjects no significant change in thyroid hormone levels was seen during propranolol treatment or withdrawal. The rise in T3 and FT3I coincides with, and may contribute to, the rebound increase in adrenergic activity after propranolol withdrawal in hyperthyroidism.