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Thyroid UK
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Taking NDT and FT4 has dropped - Dr puzzled

My GP would never put me on thyroid meds because my blood tests were always in the 'normal' range; however, I felt absolutely horrible and with my family history of hypothyroidism, I new something was up. I went to 3 different GPs and was told I had fibromyalgia, it was just menopause, it was arthritis, it was chronic fatigue syndrome etc. So I took things into my own hands - I sourced NDT and within 2 weeks was no longer falling asleep at my desk and in 4 weeks, muscle and joint pain was gone, my hair stopped falling out, I slept better, was getting up earlier - all good!

I'm always concerned that one day I will not be able to source my NDT, so I have a new GP that is wonderful and listens, but before he will prescribe me anything he wanted to take blood while on NDT and then after being off of it for 3 weeks. So here is what happened:

Before ever going on it: TSH 2.7 (0.27-4.2); Free T4 13.0 (11.0-25.0), Free T3 3.8 (3.1-6.8)

On NDT: TSH 1.21; Free T4 11.3; Free T3 (lab refused to test)

After Being off NDT for 3 weeks: TSH 1.72; Free T4 13.2 ; Free T3 4.6; Thyroid Peroxidase IgG Ab 9.6 (<34.0)

As a result of being off the meds for 3+ weeks, my fatigue returned as well as muscle/joint pain and my hair started thinning again. He is consulting with an endocrynologist and I'm to see him today. he believes that something is going on, but needs to explain it scientifically. He said if it was just between him and I he would prescribe me meds, but if I were to move or another doctor take over he wants to make sure that he can justify the prescription. I have since gone back to self medicating and feel 100% times better. My question in the long drawn out message is why would my T4 drop while on NDT?

Thank you in advance for your responses :)

6 Replies

Its pretty common for t4 to be low when on NDT

t4 is storage hormone that converts to t3 and as you are getting t3 direct from ndt your body doesn't need to store as much. the ft3 is the important test when on NDT, as long as that is top third if range, even top of range, then low ft4 doesn't matter.

hopefully someone will be along to explain properly :


I have many health issues Thyroid,pernicious anemia etc always no energy nausea unable to feel well on levo..Well am now trying something new check out Iodine and Thyroid health..I have been supplementing this for 2 weeks now and most of my symptoms have gone and my brain fog has lifted.But my doc is concerned as my blood test spike ..But I feel better so will continue this for time being. Iodine along with magnesium oil and selenium are all lacking in our modern diet


The answer is probably the changed balance between T4 and T3 taken in as opposed to T4 alone, to get the appropriate FT3 for health. With NDT a given dose will achieve a good FT3 level with lower T4 because you are both getting T3 direct and converting a little T4 into more T3 as well. With T4 alone, you'll need more to achieve the same FT3 because conversion is the only thing going on to produce T3 and there's no direct supply to help out.


Go with you gut , the NHS is useless . If you feel better on it , you need it.


Free t4 often drops when you are taking something containing t3. Don't know why dr is puzzled as it is to be expected.


Thank you everyone for all of your replies.


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