Can somebody tell me how much 200 mcg of T4 sho... - Thyroid UK

Thyroid UK

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Can somebody tell me how much 200 mcg of T4 should be in T3?


Since I am on 200 mcg of T4 I am trying to find out how much is this in T3? I don't want to take it all in T3, I just want to know the measures so I can decide how much of T4 I can substitute with how much of T3. This information is very hard to find on the internet. I tried but with no success. I sourced T3 myself online last week without prescription (my GP does't know about it and I don't have any help from her) but until I find this info I can't start with it. Thanks

16 Replies

NTH comes with T4 and T3 in a 4:1 ratio.

A rough guide has T3 as being 4-5 times stronger acting than the T4. So 200 T4 could be equal to 40-50mcg T3.

Someone may say different, so don't take my word for it.

Dr Blanchard in his books says we do best on a 98:2 ratio of T4 to T3. This means we only really need really small amounts of T3 in relation to the T4.

There is not one size fits all because there are so many variables. So trial and error is the wy to find out what suits you. This means starting off with really small amounts of T3 and building up slowly if introducing T3 to the T4.

Hidden in reply to marsaday

Thank you, you've been very helpful. I know that it can't be precisely calculated but I needed to have at least some kind of guide where to start.

It's about 3:1, see . Remember T4 has a half life of 7 days as opposed to 1 day for T3. So either move across slowly or reduce your L-T4 for a few days before introducing the L-T3.

jgelliss in reply to jimh111

Adding T-3 to already high T-4 can cause many hyper issues . Lowering T-4 before adding T-3 or NDT is advisable . Know your FT-4 and FT-3 TSH values before switching .

Hidden in reply to jimh111

Thank you. I decided to follow your advice and cut on my T4 right away. So this morning I took 150 mcg instead of 200 mcg. Will be doing this for next few days and then I'll add T3. Thanks once more.

Everyone is different; I found such ratios to be useless for me. Since you haven't even got your TSH to one or under on 200 mcg levothyroxin I am not sure you will need to reduce the T4. My FT3 went down tho I added 25 mcg T3 by dropping my levothyroxin from 125 to 75 mcg, and am still trying to fine tune the dose with T3 at 37.5 mcg., and T4 restored to what it was. Whatever when adding T3 try tiny doses like 1/8 th of a pill for first few days, and only slowly add more... took me c. 5 weeks to get up to 25 mcg. You can also try T3 at different times of day/ night: one dose with levo, or split so you have some in the afternoon. Experiment, but be patient!

Hidden in reply to Judithdalston

Thank you. This morning I already took less T4. Maybe I didn't have to but I feel somehow that too much of T4 is making me even more sick so I really don't want to continue taking a lot of it. I will then introduce T3 slowly. I am so keen to get better. I can't function properly for years now.


The problem is that there is no simple formula which does this.

Imagine if you were a "poor converter" of T4, perhaps only converting 10%. Then your current 200 micrograms of T4 would only produce 20 micrograms of T3.

Imagine if you were a "normal converter" (hey, I don't like the normal word either, :-) ), at about 30%, then your 200 micrograms of T4 could produce 60 micrograms of T3.

So any number you did find - here or on the internet - might or might not apply to YOU.

Hidden in reply to helvella

Thank you. Yes, I understood that by now. I just wanted to get some idea where to start, although I am aware that it is impossible to calculate this thing precisely. I'm aware that I will have to go though a lot of different doses before I find the right one, if I ever find the right one, but fingers crossed I mustn't lose hope :)


If you have low vitamins then neither T3 or T4 will work well

Hidden in reply to SlowDragon

I take good multivitamin with high doses of B vitamin complex, vitamin D, etc. every day for years. I also try to eat lots of veggies, fruit, healthy grains, protein. I don't know what I can do more.

SilverAvocado in reply to Hidden

Fatima49, you'll really only know if you have good numbers by getting a blood test (and even that isn't completely fool-proof). If you do have deficiencies or levels below optimal eating food and the low levels in multi-vitsmins don't help. You'll need high dose supplements, in the most easily absorbed forms and maybe other measures depending on the nature of deficiencies.

Its very common to have vitamin deficiencies with Hashimotos, as they go hand in hand. The ones to start with are Ferritin, folate, vit B12 and vit D. You may be able to get some or all of them from your GP, or places like Medichecks and Blue Horizon do them as mailorder finger prick tests.

To answer your conversion question, I've seen papers assuming T3 is anywhere from 3x to 10x as potent as T4. In my own self medicating I've always assumed 4x, and anything from 3x to 6x is common in links recommended on the forum.

It doesn't matter too much which of those you use as a rule of thumb, you'll have to use trial and error anyway. In general I prefer to start on a dose at the low end of the estimate, and increase up later to try and find the sweet spot. If you suspect your dose is too low at present, you might as well estimate on the high side, and give your yourself a slight dose increase when you change. We're always limited by the tablet sizes when doing this, too, so you'll always be rounding up and down a bit.

PS: you sound v clued up already, and I think all the plans you've mentioned in the thread sound sensible.

It's hard to say as people react differently to T3, but between 50 and 65 mcg (probably)

Hidden in reply to Angel_of_the_North

Thank you.

I would find out how much T3 I was generating from each T4 dose level. When I was on Levo (T4 only) I felt lousy and was not generating hardly any T3. As I crept up in my Levo dose I hit a level where I suddenly began to generate T3 and I felt well.So, I advise getting a full thyroid panel as your baseline before you set out on this experiment. Each time you increase your dose of T4 do another measurement (just of free T3 and Free T4 this time - to keep costs down - oh and throw in TSH). If your own T3 generation flattens out then assess how you feel, if good, stop there, if still lousy consider adding a tiny amount of T3 (cytomel or some equivalent). When you start adding T3 externally watch your pulse and blood pressure levels, drop back to the previous dose if either gets too high. Sadly we have to give the heart precedence over the thyroid. For me I just get tired much earlier than I used to - so no more late parties - but at my age, that's OK. But other than that I am really well.

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