Very interesting information if any of you have been put on the above combination of drugs!
I looked up the manufacturer info about levothyroxine interactions and it says a) that levothyroxine increases uptake of propranalol (beta blocker) and b) MOST interestingly that beta blockers impair conversion of t4 to t3!! So that would explain high t4 and high tsh at the same time.
A bit of background - my GP overdosed me on levothyroxine after discovering my tsh too low. Then gave me beta blockers to treat hyperthyroid symptoms (30mg/day). Then increased dose to 80mg day. At this point I started blacking out, muscle cramps, pins and needles, numb face, couldn't walk down Street due to intense faintness, basically felt I was dying. And meanwhile tsh and t4 both too high on blood tests. Finally A&E noticed I shouldn't be on propranalol and levothyroxine at same time and been off them 7 days now and faintness etc has gone away. Would NOT want anyone else to go through this so wanted to warn you all - do not let doctors put you on high dose beta blockers without carefully monitoring effects including on your thyroid levels!!!