Thyroid UK
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How should I phase out T4 to T3 only?!

Hi all, I'm on T4 100 mcg and 10 mcg T3 and have been for nearly 18 months. I used to be on 125mcg T4 and 20/24 mcg T3 before that but my NHS doctor removed T3 completely and my health did a u-turn. I felt much better on the higher amount but can't say I have ever felt totally 'well'. Since being back on T3 alongside T4, I have been better but am very up and down and am feeling awful at the moment. I was diagnosed 15 years ago from symptoms by the wonderful Dr Skinner who saw I had a conversion problem even then - T4 on its own did nothing. I have just this year found out why - I have the defective DI02 gene.

Because of this, I am interested in trying T3 only to see if it helps. How should I do this? Do I need to come down incrementally on T4 first and if so, how much by and for how long? Or can I just remove T4 straight away and raise my T3 doses until I feel good? How long should I leave it to judge if it's working?

I am trying to get time to talk to my doctor too but his surgery is closing soon so am at my wit's end and need advice. Sorry for all the questions - please help!!

10 Replies


DIO2 gene can impair T4 to T3 conversion but adding T3 to T4 overcomes it. There's no need to switch to T3 only.

Can you post your TSH, FT4 and FT3 results and ranges on 100mcg T4 and 10mcg T3? It may be sufficient to reduce T4 a little and increase T3.

If you are determined to switch to T3 only you can switch straight over. 100mcg T4 is equivalent to 30mcg T3. You should have a FT3 test 6-8 weeks later to ensure FT3 remains within range.


Thanks Clutter. Last test results in June as follows - although NB done in the afternoon (around 2pm) and I had taken medication that day also:

TSH: 1.19

Free T4: 18.91

Total T4: 105

Free T3: 7.06

RT3: 28

Prior to that, test results in Oct 2016 (again I had taken medication but these were earlier in day around 12.30pm):

TSH: 1.06

FT4: 21.07

FT3: 5.7

RT3 not taken

My symptoms at moment are tiredness, depression, cold and tingling feet and hands, hair falling out in shower more than it should, lack of energy and enthusiasm.

I feel that T3 is key for me, more than T4 (when on T4 only, I reacted very badly and felt over and under at once - jittery, exhausted, palpitations, shortness of breath etc)... But will try your recommendation of bringing down T4 and upping T3 first. And am also trialling taking T3 incrementally through day as had never done that before.

Thanks for help - Any more tips gratefully received.



Can you edit your post by clicking on the v down arrow underneath and add the lab ref ranges to your FT4 and FT3 results? How long before your blood draw had you taken T3?


Hi Clutter,

I tried editing but couldn't post so here are results with ranges against them. I would have taken medication at around 7/8am on both occasions (although can't say that exactly but it would usually be when I woke up - I've only just started splitting T3 through the day so took all at once before).

Thanks for your help - really appreciate you looking for me.

June tests - taken in the afternoon (around 2pm) and I had taken medication that day also:

TSH: 1.19 (range 0.27 - 4.20)

Free T4: 18.91 (range 12-22)

Total T4: 105 (range 59-154)

Free T3: 7.06 (range 3.10 - 6.80)

RT3: 28 (range 10-24)

Prior to that, test results in Oct 2016 (again I had taken medication but these were earlier in day around 12.30pm):

TSH: 1.06 (range 0.27 - 4.2)

FT4: 21.07 (range 12-22)

FT3: 5.7 (range 3.1 - 6.8)

RT3 not taken



Levothyroxine and T3 can peak in the blood for up to 6 hours so it is possible they were still peaking when you had your blood draw at 2pm. TSH would have been higher had you tested early in the morning.

rT3 is over range so it might be helpful to reduce your Levothyroxine dose to 75mcg and increase T3 to 20mcg. If you are determined on switching to T3 only 100mcg T4 is equivalent to 30mcg T3. I would split 40mcg into 2 doses, morning and bedtime.


Hi Clutter, sorry - One more thing. If I did decide to do T3 only, should I gradually reduce T4 and by how much each day / week? Or just switch straight to T3 only (will trial your suggestion of 75/20 first). Thanks!



It's really up to you but IMO T4+T3 is a smoother ride than T3 only so I would reduce T4 and increase T3 dose every couple of weeks until you hit a sweet spot.


I really believe that we should begin T3 very slowly. 5mcgms twice a day to begin with then gradually increasing by 5mcgms each time with a week in between.


Thank you!


Thanks all.

Clutter - I had thought T4 75mcg / T3 20mcg in two doses was probably the best place to start too so appreciate your advice on that. I'll try that first.

Kathleen-1 - many thanks for your advice too. I've been on 10mcg for over a year (alongside 100mcg T4) so already acclimatised to that amount (I was on it at a higher dose for over 10 years before that before being taken off it by a doctor who didn't understand it and I felt awful)... But if you mean when taking it on its own, I will definitely keep your advice in mind.

Thanks so much!


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