Beta blockers, T3, and T4
Propranolol is used to treat thyroid storm specifically because of its action in blocking conversion of prohormone thyroxine (T4) to triiodothyronine (T3) (“Do beta blockers cause depression?” Medicine in Brief, Current Psychiatry, May 2010). Because T3 is the basis of the basal metabolic rate, if T3 were decreased then the only other mechanism for energy is adrenaline. This would cause depression when adrenaline wasn’t in use and anxiety when it was. This sounds like a direct link to depression and anxiety to me. The thyroid function test would show no change in thyroid-stimulating hormone, but an increase in T4 to compensate for the decrease in T3. There are no medical standards to routinely look at T3 and the effect would not be seen anyway. I am not aware of research that explores this connection between beta blockers and depression.
John V. Billings, ARNP