t3 or t4 suppress TSH the most?

[lisan1]

Which of liothyronine or levothyroxine suppress TSH more or is it the same effect for say 25 t4 and 5 t3,

[diogenes Remembering]

It depends very much on the state of your thyroid. If some is active, this is a totally different situation from when none is. Put broadly, if any thyroid remnant is working, then T4 is produced, albeit at a reduced level. What T4 there is, is converted to T3 at the level of tissues and glands. But the thyroid in this situation desperately tries to keep the system going by producing T3 direct at the expense of T4. So in this case, local T4-T3 conversion still has a big part to play. If there is no thyroid whatsoever then of course the system is totally destroyed. So routinely T4 is given, in the belief that it will be converted to T3 adequately in all tissues. For the majority of people this works, but for a minority no amount of T4 will give adequate amounts of T3 - they simply cannot convert enough T4, without the help of the thyroid's T3 production (which of course doesn't exist with no thyroid at all). So the answer would be: if you have some thyroid working then T4 conversion + thyroid T3 will try to save you from a deficit. If you have no thyroid, this is a different situation. NB: for people on T3 only - there is no conversion of T4 obviously, but the only source is from taking the pill. The organs like local conversion principally to satisfy their needs but that isn't possible on T3 alone. So it takes more taken-in T3 to satisfy the organs, resulting in suppressed TSH. Thus, there isn't a quick answer to your question.

[lisan1 in reply to diogenes]

So, if I wanted to try to get TSH back in range what would you decrease levothyroxine or liothyronine? Results on 100 t4 10t3 isTSH<0.01

Ft3 5.1(3.6-6.3)

Ft4 19(12-22)

My TSH had been suppressed for 4 years.

[diogenes Remembering in reply to lisan1]

It's probable you may not get detectable TSH back, or at the best get it just detectable, after all the time it has been suppressed.

[lisan1 in reply to diogenes]

Thank you so much. Would it be ok to have it suppressed? Which of the 2 (levo or lio)would you decrease if I would like to try to get it within ref again?

[diogenes Remembering in reply to lisan1]

Don't go by the TSH. My wife has had undetectable TSH for 50 years on T4 only with no problems. It's only an anecdote but it shows that one can live perfectly well with no detectable TSH. I would say, look to your own well-being rather than numbers.

[Cat013]

I reacted massively to levothyroxine. My TSH practically vanished on 75mcg of it. I’m now on 25mcg of T3 as well as 100mcg of levo and my TSH remained the same (0.02) as on t4 only at my recent blood test. I guess we’re all so different. But so far for me personally t4 wiped it out way faster than t3.

[jimh111]

I'm asusming you mean in tablet form. It seems from patient experience that T3 has more effect on TSH. Possibly this is a result of single daily doses and splitting doses may reduce the effect (this is just speculation).

The evidence is that T3 is 3x as potent as T4 in supressing TSH ncbi.nlm.nih.gov/pmc/articl... . A further consideration is that levothyroxine monotherapy may just not work for some patients.

[Bearo]

My TSH dropped from 4.98 to 0.91 on 50mcg Levo and to 0.09 on 75mcg Levo. With T4 and T3 both 40% through range I wanted another increase and I’m now on 100mcg. But with such a low TSH it’s hard to get dose increases. I don’t understand why it’s dropped so much or what it means. I just read on here that it doesn’t matter.