I just wondered why people changed from a combination of T4 and T3 to T3 only? Do you feel better or different? And how does it affect your blood tests doing this?
If you are hypothyroid and take T3 only - what in your body produces the T4 to show up in a blood test? As presumably your thyroid isn't working so cannot produce T4? Or does the thyroid partially work and so produces some T4?
Good question and I'll be following. I've just gone from NDT to t3 only three days ago. I want to improve the hypo symptoms I still have. But can't answer your question
Some people on T3 won't produce any T4 at all. Some will produce a little. It really depends on the cause of the hypothyroidism.
I've been on T3 only for just over a year, and my last results looked like this :
TSH 0.11 mU/L (0.27 - 4.2)
Free T4 1.94 pmol/L (12 - 22)
Free T3 4.1 pmol/L (3.1 - 6.8)
I had "ordinary" results for a mildly hypothyroid person before I had ever been medicated (over the range TSH, very low but in range FT4 and FT3), and yet I felt a thousand times worse.
I produced high levels of reverse T3, which was obviously a contributing factor to how I felt, but the NHS never measures rT3, and pays no attention to it if you get it done privately.
It was the high rT3 which made me switch to T3 only. I haven't regretted it yet. 
I was on T4 for 17 yrs.Reduced it and added T3 in 2015.Some symptoms improved(eg hair loss slowed right down) but other hypo symptoms remained.I believe prolonged adrenal fatigue due to prolonged stress was an issue for me.
Decided to try resolving my adrenal issues with Paul Robinson's T3-only protocol.Upped my iron,B12,folate,D3,magnsium,zinc(also by changing to more bio-active formulas)also take omega 3s,vit C.
Now feel I am improving slowly but remarkably,especially since going GF & starting LDN
Redhotchestnut, I believed I had a build up of unconverted T4 and T4+T3 wasn't relieving symptoms so I went T3 only for 3 months to clear the build up after which I was able to resume T4+T3.
I just recently started with only T3. I did tried that before while clearing my rT3 but then I felt much better than of both T4 and T3 so I recently decided that from now on I will take just T3. I really don't need T4 I am feeling so much better like this.
I would be very interested in the transition process from T4+T3 to T3 only.
I have gradually increased my T3 and always feel better for a relatively short time before what feels like some hypo symptoms return. I am currently taking 25mcg T3 and 75mcg T4. I found that 50mcg T4 felt too little, and maybe 75mcg is too much.
Although I do not have obvious Hyper symptoms (which I had in the past when I was on 125mcg T4 only), I am experiencing tremors, but this does not seem to change when I have tried lower doses.
I am beginning to wonder if rT3 is complicating things?
So, if I stop taking or reduce T4 for a while (how long?), I could feel better (if rT3 is clearing) or I could feel worse (if under-medicated).
Lots of different reasons so it seems? Thats interesting Clutter - a build up of unconverted T4 in the system - how did you work this out I wonder? As I've been on T4 for so long now with symptoms still here and questionable if I convert to T3 as well? So could I have some unconverted T4 in the system sort of clogging things up?
How do I check my Reverse Levels of T3 please humanbean, would that be on a Blue Horizon blood test I might have had done?
Magnesium time! What does everyone do? So many choices - how to decide?
Vegovy 
Changing beta blockers
Unraveling the molecular architecture of autoimmune thyroid diseases at spatial resolution
