Why stay on Levo when changing to T3? - Thyroid UK

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Why stay on Levo when changing to T3?


What are the benefits of taking Levo and also T3? My GP took me off my 150/175 Levo 3 weeks ago, and I am now on 40mcg T3 daily. He said he didn't know why people would stay on Levo when transferring to T3. He and I wonder if I have a conversion problem. Though he did say he hadn't used it much, so didn't know a huge amount about it. I definitely feel a lot better, now feel able to actually do things I see that need doing.

But why do people use a mixture of both?

15 Replies

Because of some vague terror that if the t3 runs out, the stored t4 will miraculously convert?

I Have never understood it either, not if you can't convert. I have seen claims that there are t4 receptors in the brain, and also that t3 cannot cross into the brain.... But people seem to survive just fine on t3 only.


Conversion doesn't work well in any case if your minerals etc are low as they offer are in thyroid sufferers. Have you had your folate Vit B12 and Vit D3 tested? They need to be optimal which is usually high I. The range. Folate and D I was under the ranges!


I'm a poor converter but T3 added to T4 overcomes that and may stimulate better conversion. I prefer T4+T3 combination to T3 only. It's a smoother ride with less peaks and troughs than on T3 only and I do like the security of having some T4 in my system should I be unable to get or take T3 for a few days.

Naomi8 in reply to Clutter

Clutter-I believe I am also a poor converter,not a non-converter.Got rid of all the T4,which I believe had built up to a toxic level,& was T3-only for 8 months.Now adding some T4 back in with some NDT.

Mixed results!Weight(water)loss,feeling a smoother ride but mild ectopic beats return & 2 episodes of my old pal supraventricular tachy(heart rate doubled from 5pm yesterday til 3am today).Loathe to give up on the NDT,not planning to drop T3.

As everyone on this thread says,we have to try to find what suits us.Heart consultant said-don't come back to A&E if you get an episode,don't bother with betablockers,sit it out.I did!

We need courage!I couldn't do this without this forum.

Clutter in reply to Naomi8


If NDT means a return to ectopics and tachy I wouldn't persist if I had been well on T3 only. 10 hours is a long time to sit out a tachy episode. You must have courage in spades!

Naomi8 in reply to Clutter

Thank you Clutter.I think you are right.I have also noticed a slight increase in morning "unease"& a mild dip in mood.Just need feedback like yours to help me make a decision!

faith63 in reply to Naomi8

t3 has no peaks and valleys and is very smooth..Dr. Lowe studied t3 for years and it is better,superior to t4.

Some people feel better when they are taking both. Some feel better on T3 only. We're all individuals, and all need different things, and the name of the game is finding what suits each individual patient. So, try a little T4, see how you feel. If you feel less good than on T3 only, just stop the T4. But, if you Don't try the different combinations, how will you ever know what's best for you?

It isn't difficult for your doctor - or you! - to find out if you are converting correctly. You just test the FT4 and the FT3 at the same time. If you are converting correctly, your FT3 will be higher than the FT4 in their respective ranges. If you are not converting, then the FT4 will be higher. :)

Naomi8 in reply to greygoose

greygoose,does this apply to blood testing FT3 & FT4 when on T3 & NDT?

greygoose in reply to Naomi8

When you are taking T3 in any form, TSH is usually going to be low/suppressed. FT4 is going to be low because the body doesn't hang on to so much. The only helpful test when taking T3 is the FT3. So, no you cannot tell how well you convert when taking T3 because you no longer have to convert so much.

People use a mixture because that is the way the body "normally/naturally" functions. However, I have run into people who cannot do conversion, at all; for them the only solution is T3-only. Personally, I have done well on T3-only, but I am pretty sure now that concentration swings of T3 in the blood, are less when on T3+T4.

The bottom line here is: medicine is an experimental science! That is something that many doctors just don't get. You have to experiment, experiment, experiment to find the combination (T3-only, T3+T4 or NDT, NDT+T3, T4-only) that works best for you.

faith63 in reply to Eddie83

the blood fluctuates, maybe, the cellular level is steady. i have had my blood concentration of t3, look fine 24 hours after the last dose. t3 lasts between 1 and 3 days.

I totally agree that we are all different, and I also think that we all need to get as close to normal functioning as we can. So, as I had my thyroid gland removed, and T4 only left me undermedicated for many years, I now add T3.

Our bodies would normally produce mostly T4, but also 10-20% T3, so I am not surprised that I am now feeling improved, taking the same amount of T4 as I took for about 15 years (always a little above range when tested). I now add just 12.5mcg T3, which seems to be stimulating better conversion, as my T4 is now only just above mid-range, and my T3 level is improving.

Trial and error is the only way forward. It's sad that most doctors are not brave enough to work with us to do it, but we have this website to help. Thanks very much to the website and all who contribute and support!!!

you do not have to stay on levo. if you don't convert well, the levo will block the action of the t3 or you will not be able to take a large enough doe of t3, to see improvements.

I think I have just proved that,faith 63.Six weeks of T4 in the form of NDT,added to my T3 & reducing my T3,saw a return of ectopic beats & supraventricular tachycardia,plus a return of mild anxiety in the morning.I am glad I experimented,but its back to 50-55mcgs T3 for me,in split doses.I would love to take it in one dose,but my heart pounds,without speeding up.

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