Thyroid UK
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Conversion problem


How (and how quickly) can you tell if you have a conversion problem of T4 to T3. I have been put back on Levo plus a little T3 but I had bad problems with Levo earlier this year when I became toxic and am very worried this might happen again.

I Have also been told (by P Robinson et al ) that my iron is going into storage..whatever that that may be what made my recent T3 mono trial fail . And will this affect me on T4 and T3 ? I can get an private blood iron panel done but dont think my doc will pay any attention as usual.


5 Replies

Daffers, conversion issue usually shows up as low TSH, high in range FT4 and low FT3. I think you'll need to give it 3 months once resuming thyroid meds to tell as TSH reacts quickly but FT4 and FT3 lag behind.

I had a hideous time on T4 montotherapy, was a little, but not much better on T3 only but I'm well on T4+T3 combination. I hope it works for you.


Thanks CLutter.

When you started the combination, what ratio did you use of each please ? I was struggling on T3 alone and unable to raise beyond 18.5 (Cynomel) per day, but didnt feel well and was constantly anxious and on edge.

I asked the Endo if I could try some T4 with it and he has dropped me straight down to 1/4 of Cynomel plus 50 of Levo a day, which he says is the natural ratio. I had hoped it might be more gradual decrease of T3 or just adding say 25 Levo in to the mix.

Prior to all this, in May, I was quite unwell on Levo alone, and am frightened of the problems recurring. II have got palps now and no idea why - low thyroid hormones, or anxiety. I have also lost my appetite again - which happened last time my hormones got low.

Grateful for any comments



Andrea, I'm thyroidless so my dosing isn't likely to be helpful to you. It may be better to take a little more T3 until the Levo has built up in 7/10 days. I didn't feel my endo was helping me so self medicated until I found a dose on which I felt well and then he agreed to prescribe at the dose I felt good on.

Post surgery I was prescribed 60mcg T3 and was okish. Post RAI I was prescribed 200mcg T4 which made me feel poisoned. FT4 and FT3 remained very high above range for 7 months by which time dose had been reduced to 125mcg and I still felt poisoned. On 100mcg FT3 dropped below range and I felt worse. I added 20mcg and felt a little improvement. 6 weeks later I stopped T4 and over the next couple of months tried 60mcg-120mcg T3 but still felt terrible. Stopped all meds for 4 weeks to detox and felt better after a week. Resumed 100mcg T4 and felt dreadful within 3 days so added 20mcg T3 and felt well. Raised T3 to 40mcg when I ran out of steam when I became more active. Reduced T4 to 75mcg + 40mcg T3 when I felt too hot in June.

TSH is 0, FT4 dropped to 14.9 and FT3 elevated 8.4 so I'm dropping T3 to 10mcg and increasing T4 to 100mcg. Endo suggested sticking with 75+40 but I felt better with higher FT4 and lower FT3 plus I've just been diagnosed with mild osteopenia so I figured reducing T3 may be a better option.


Blimey sounds like you've really been through it and learnt a lot on the way. Thanks for sharing with me. I felt I might need a little extra T3 in for the first week or so so its reassuring to get your views. I must be braver about self adjusting my meds a little. I really felt I missed the T4, altho lots of others just love T3 only.

Can I just ask, did you have any conversion problems ?

Also did you ever try any of the NDTs


Daffers, I was converting on 125mcg-200mcg T4 but T4 only made me feel very ill. On 100mcg I wasn't converting and needed T3. 20mcg T3 calmed the adverse side effects of T4 and improved my FT3 level.


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