Help with NDT dosing - is my FT3 too high? - Thyroid UK

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Help with NDT dosing - is my FT3 too high?


Hi all,

I started taking NDT (NP Thyroid) two months ago, after taking Levothyroxine (120mg) for 10 years for diagnosed Hashimoto's Thyroiditis. I've been on a two grain dose for six weeks now although I still have some of the symptoms that have been plaguing me: insomnia, anxiety, brain fog, very cold feet, dramatic hairloss (alopecia areata) etc

My NHS GP is supportive and focused on symptoms although doesn't really know much about NDT so although I had a blood test including FT3 last week he didn't really know what to say...

Serum free T4 level 14 pmol/L [9.0 - 25.0]

Serum TSH level 0.17 miu/L [0.3 - 5.0] - Outside reference range

Serum free triiodothyronine level 11.1 pmol/L [3.5 - 6.5] - Outside reference range

Note: I took my meds at about 7.30am and the test was at 9.30am. I'm also taking the full two grain in the morning as taking even a half grain in the afternoon seems to make it hard for me to fall asleep.

I guess the question is whether to increase and see whether that helps the symptoms or decrease to address the high FT3 levels?

Other things to note:

Also, although my Vit B12 and D levels were fine, I've been taking supplements for about six months: magnesium (for sleep), B-complex, Vit D, Iron. I been having palpitations so that could be the FT3 or the magnesium. I've come off all these supplements for now to see and the palpitations seem to have stopped so it might be that was the problem.

I've also been off gluten since November (after reading Izabella Wentz's book). I did a full hormone panel in March (DUTCH urine test) which indicated that my adrenal function was normal although I was very estrogen dominant - so I'm using a progesterone cream. Another test showed below range glutathione, so I'm also supplementing that.

Hopefully all of this will help but advise on NDT dosing would be very welcome!

Thank you!


9 Replies


You have a false high FT3 due to the fact that you took your NDT before the blood draw.

When testing we should leave off NDT (and T3) for 12 hours. The T3 in the NDT will peak in the blood 2-6 hours after taking it.

Even allowing for the fact that you took your NDT close to the blood draw, I think you may be overmedicated.

Even allowing for the fact that you took your hormone before the test - you should leave 12 hours between the last dose and the blood draw - your FT3 is too high. I think we take away 20% from the result, which still makes it 8.88, and that is well above the top of the range. So, I think you need to reduce your dose.

Someone correct me if I'm wrong? Does the 20% rule still work for NDT?

I agree with Seaside Susie and Greygoose. Going from 120 mg. levothyroxine to 2 grains of NDT is a big jump, particularly due to the sudden addition of T3. If I ever switched dosing like that, I'd be totally wired, hyper and not sleeping.

For the switch I would have started off on one grain NDT for awhile, split into 2 doses, which based on conversion charts is approx. equal to 100 mg. levothyroxine. (These charts are not exactly accurate, but at least you won't dangerously overmedicate if you check them.) The addition of some T3 may have made you feel good for awhile.

If I eventually felt tired on that dose, I would have moved to one and a quarter grains and then one and a half grains of NDT. Two grains sounds like you are overmedicated.

Some, like myself, take some levo and some NDT. That is another option to try to keep your T3 from getting too high, while still replacing T4.

I get my labs done 20-24 hours after my last dose. Much of my T3 from NDT has declined by then anyway. I then know what it measures at my lowest point vs. my highest point.

Thanks for these replies. I think the brain fog helped me forget that I was not supposed to take the medication before the draw!

Based on what you say, I should definitely reduce my dose. I suspect that everything else I've been doing may have also helped my overall thyroid function too. Plus I usually find I can reduce my dose in the Summer months.

Should I drop my dose incrementally i.e. by just 1/2 grain now? And a full grain if that doesn't help?

I'll also think about taking some Levothyroxine with some NDT as well, as another option. I didn't realise that people did that!

I wouldn't bother adding levo to NDT - doesn't seem to be any point, just reduce NDT by 1/4 to 1/2 a grain and retest in 6 weeks. 1 grain NDT is actually "equivalent" to 65 to 75mcg of levo (if you do the maths), but may affect you like a higher dose if you are specially sensitive to the T3 and convert well.

It's not going to be easy juggling with two different things. Better to get the NDT dose fine tuned. I went from 100/125 Levo to 1.75 though at the monent on 1.50/1.75 trying to see what I am like on 1.50 as my reading had gone up a little probably as other things have kicked in.

Optimal, if it were me, I would probably start by dropping my dose of NDT by 1/2 grain now. And I would take my 1 and 1/2 grain daily total dose of NDT split into two daily doses, one morning and one afternoon, at least at first.

If you are still a bit wired after a short trial of this, try going down to one grain per day and stay on that for awhile and see how you feel.

I find when I'm on NDT only with no levo, one grain per day is all I need. Everyone is different though, and this depends on a variety of factors.

Optimal in reply to Gates

Hi Gates, I really appreciate your advice on this. I've dropped to 1.5 grains and will split the does. I assumed that I needed to 'match' my Levo dose with NDT but as you say, I'm may actually be fine on less.

Hi Optimal, I recall you said your doctor doesn't know much about NDT. It appears he was right in that regard. He should have checked conversion charts.

He replaced your 120 mg. levothyroxine that you were taking with 120 mg, (i.e., 2 grains) of NDT. An even exchange. The problem is that the natural thyroid hormone is much stronger. 60 mg. NDT (Armour, for instance) is approximately equal to 100 mg. levothyroxine.

In fact, I feel a lot more peppy on 60 mg. Armour NDT than I do dragging around on 100 mg. levothyroxine, due to the T3 in Armour NDT.

So in my opinion, to be safe, he should have started you on one grain of NDT since you are adding T3 suddenly, which you are not used to. (Some people react very strongly to it.) An equivalent dose to 120 mg. levothyroxine would be one and one quarter grain of Armour NDT, or 75 mg.

Some argue that conversion charts are not exactly accurate. But I always consult them to be safe. You do not want to overdose on T3; not a fun experience, and dangerous.

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