Synthetic T4 to NDT conversion

How do I convert my T4 dose to NDT?

This is a question one sees often in the thyroid Facebook groups. There is a lot of confusion and insecurity around this. Which is not so strange, as there is very little good info on the topic. Here are my recommendations

The conversion tables the NDT (thyroid) producers themselves provide are ridiculously low. They are wrong, wrong, wrong. I don’t understand how they think at all. If they do. Think. One would be seriously under dosed if adhering to those guidelines. And if one’s doctor reads them, one could get serious problems. I don’t know how many doctors read these instructions. I hope they don’t. Here is a table from Nature Troid as a (bad) example.  

Everybody on NDT knows, this is way off. 100 mcg T4 equals 1 grain NDT?  Most NDT’s contain 38 mcg T4 and 9 mcg T3. (NB! There are exceptions. Erfa contains only 35 mcg T4 and 8 mcg T3, in Denmark we have Glostrup with 31mcg T4 and 8 mcg T3). But this should replace 100 mcg of T4? NOT. 

Thyroid patients Canada (TPA) also adress this issue. And that is positive. But then they highlight the conversion table from the Hoang 2013 study. They claim, that is better as it gives slightly higher doses NDT to T4. I disagree. I wish they hadn’t drawn attention to it. I have communicated with them on this. TPA and I agree on many things, but no on this. They say it is built on science. Might be, but it is bad science. Why? Because all the participants in the Hoang study were under dosed.  I know TPA goes deeper into this in their underlying article. But many never read the article, and the table might be taken out of context. 

We all refer to this Hoang study, it’s the one showing that 48% preferred NDT to 29% T4 medicine, Hoang et al. 2013.  And that is great, but it doesn’t change the fact that they were under dosed. They aimed for a TSH between 0.5 and 1.5. We all know that most people on T3 containing medicine are not optimal unless TSH is suppressed. They didn’t even test for FT3 in the study, reverse T3 yes, not FT3. In my opinion, if a scientist studying the effect of T3 containing meds doesn’t measure FT3, he or she does not know much about thyroid treatment. I will review this study at some later date.    

I don’t really want to publish  Hoang’s table. Things can be taken out of context and misunderstood.

Recommended Conversion Based on Results From This Studya

L-T4, μg 88 100 112 125 137 150 175 200 250 
DTE (mg) 60 68 76 85 93 102 119 136 170 


For conversion: 1 mg DTE = 1.47 μg L-T4.

Hoang et al., 2013

These doses are ridiculously low. No one gets optimal on these doses.  I have seen people in the US and Canada getting NDT as their first thyroid medicine. And that some of them can do with small doses, so small that they don’t even get suppressed TSH. They must still have some thyroid hormone production of their own. I don’t  think anyone here in Scandinavia at least, get NDT as their first medicine. It’s only after we no longer can maintain a decent FT3 level that we get that option. IF we are lucky! 

I think people should try T4 medicine first. If they convert well, as we often do in the beginning of our disease, there is no need of expensive NDT. The T3 we convert ourselves, will always be more comfortable than any thyroid meds.

If you can’t get NDT from your doctor, there are options. Have a look at this post, Our thyroid medicines


Thyroidblog's conversion table for T4 to NDT

My conversion table is meant for those with a too low FT3 on T4 medicine.  I believe it is mostly us who get NDT. I don’t see the point of taking T3 medicine as long as one is converting and maybe producing from the thyroid as well. There would be a point in taking an organic medicine though. There should be organic T4 and T3.  

How much NDT you will need, depends of course on your levels on the T4 meds. If you were underdosed, you will probably need the higher dose, or more. But I doubt many will need less than the lower dose. 

Everything thyroid is individual. One sees that in all studies on those without thyroid issues. And when we become thyroid sick, it continues to be that way. But these are the doses I see people end up on. 

If you are on synthetic T4/T3 before starting NDT, you cannot look solely at the amount of T3 you take at present. And then try to substitute the exact amount T3 in the NDT. You will need MORE T3 in the NDT. Because you will get less T4. And synthetic T3 and organic T3 are very diffent. So don’t think, I cannot handle more T3 than I get at present. T3 in NDT feels different, softer, more mellow.  

If you take 100 mcg T4 +10 mcg T3 today, you will probably need at least 150 mg NDT. If you take 100 mcg T4 and 20 mcg T3, you will probably need at least 180 mg NDT.

HOW should I start NDT?

There is as much talk and confusion around HOW to start NDT, as there is about converting T4 dose to NDT. People do it in various ways. In Sweden and Finland, they phase NDT slowly in as they phase the synthetic out. It seems to take weeks, and even months. That is not the way I would advice doing it.

I advice quitting the synthetic one day, and starting NDT the next. But  you cannot jump to a large dose right away. For one thing, the half time for T4 medicine is 1 week. That means, after one week you still have a lot of T4 medicine in your body. The half time for T3 is 24 hours. So you must take that into account. Plus, if you have been on T4 mono therapy , you need to adjust to the T3.

I recommend quitting the synthetic one day, and starting NDT the next. But how?


Stop your T4 medicine.  Take 60 mg NDT on day 1, if you have been taking 100 mcg T4 or more. Have you been taking less than 100 mcg, start on 30 mg.

After 1 to 2 weeks, increase with 30 mg if you have been on 100 mcg T4 or more. Increase with 15 mg if you have been on under 100 mcg T4.  

After 1 to 2 weeks, increase again. 30 mg for the high dose, 15 for the low. Now you are on 120 mg  or 60 for low dose. 

I write 1 or 2 weeks, because you will need to feel as you go along. If you feel too high, palpitations, sleeplessness, loose stools. Reduse with 15 mg. It’s good to take one’s temperature. Take it under your arm for 10 minutes before you get up in the morning. If it is under 97.9 F / 36.5 C, you are too low. If it is over 98.6 F / 37 C in the afternoon, you are too high.  An old fashioned thermometer is best.

Stay on this dose for 3 weeks, then do a test. TSH, FT4, FT3. Then regulate the dose according to that. When you take T3 contaning medicine, it’s best to take a bloodtest app. 12 hours after last dose. That gives the most correct FT3 level, as FT3 stays pretty level the first 12 hours after intake. After that it starts to go down.  

Remember to take the test befor 9AM. And relax, this is not that difficult. If you become a little high, the half time of T3 is only 24 hours, so it will not last very long. You need to check your iron levels before starting up. If you are low on your iron, you can get palpitations. Natural progesterone creme, Vitamin K and magnesium also calms the heart for women.  I believe we suffer more from palpitations than the men. Low cortisol can also influence how well we do on T3.

You find info on optimal thyroid levels here 



This is much easier, of course. You are used to the T3. You can switch over pretty much 1:1.  BUT you need to start a little lower than what you think you will end up on.  As you will now get less T4 in the NDT. But the first 2 weeks at least, you will have a high level of synthetic T4 still in your body. Here in Denmark, many get so low doses of T3, so it is almost like not taking it. Then your switching over will be more like for those who have been on T4 mono teraphy.  Have you only taken 2.5 to 5 mcg T3 before, you will get much more T3 now. Then it would be prudent to increase more slowly. For those who have taken 10 to 20 mcg T3, they will most likely end up on doses containing more T3 than that. 

The same goes for body temperature, palpitations and optimal values as  for switching from T4 mono. So look there.  


When to take your dose

People like to take their dose at different times. Many take their T3 congaing meds only during day time. In Norway, many take their dose, or part of their dose, at night. This is because, in healthy people, FT3 increases at night. It begins rising around 9 PM, reaches a plateau at Midnight and stays there all night. 

I take 1/3 of my dose at bedtime. And no, one doesn’t become awake. T3 takes a couple of hours before kicking in.  I take some NDT in the morning and some around 5 PM .You must figure out, what is best for you. Some set the alarm 2 hours before they are getting up, and take some T3 there. This is to have T3 for the cortisol production taking place in the early morning. I tried that a few years back. But didn’t like it. I could not fall asleep again.  I like taking it at bedtime much better. 

I hope this will be helpful. Don’t be afraid or worried about switching. NDT is the best thyroid medicine in my opinion. I don’t think mixing it with synthetic T4 medicine is a very good idea. They do that a lot in Norway and Sweden. To keep TSH up. I believe many have side effects from the synthetic T4 without being aware of it. I think everybody should at least try NDT only.

If your FT3 doesn’t get up where you need it to be, in upper quarter of reference, together with a FT4 not over mid reference, then it might be better to add a little synthetic T3 than increasing the NDT further. It’s best to avoid a high FT4 when one takes T3 containing meds. We don’t need all that T4. But I have seen a few people, saying, I need a higher FT4 on NDT. We don’t do that much in Scandinavia, adding T3 to NDT. But I see they do it in North-America. I have tried it. But I don’t like synthetic T3. It makes me nervous.

I hope these ridiculously low conversion tables soon will be a thing of the past. No one in their right mind would dose according to them. The producers don’t know anything about dosing. I see some of them even advice, taking one’s whole NDT dose in the morning. So they know nothing about the half life of T3, or the need for good T3 levels during the night.


  1. Judy Bruce

    I live in Canada and was diagnosed in 2007. My doctor put me on Synthroid and kept me on it. When I had some problems last year she refused to prescribe T3. I am not sure where you heard that NDT is the first drug that we get, but it is not true according to my history and the Facebook groups that I am on. I am just starting NDT now and I had to go to a naturopath for it. Yes, we are also kept under-medicated all the time and they have no ears for our symptoms.

    • L S-L


      I am sorry to hear that, and I hope the NDT will change things for you. It has for me, as long as I take enough of course. I hope you have a look at this post, if you are unsure, what are good thyroid levels, Optimal thyroid levels.

      I didn’t mean to imply, everybody in Canada start on NDT. I will word that differently. I have seen people in Canadian thyroid groups, starting directly on NDT. And even more, in the US. Maybe they are people who go to naturopaths and have been diagnosed by them. I know that thyroid disease treatment is not good in Canada. That it can be difficult to get the proper tests and so on.

      Best of luck, Liv


    Hi. Thanks for the great article. What is your conversion for pure T3 to NDT and pure T3 to T4?

    • L S-L

      Hi Michael!

      I am sorry, I don’t have any for T3 mono. The conversion rates I give, are based on my own experience with T4 and NDT, AND what I have observed over the years in thyroid FB groups. There is no science behind it, as science in this area is useless. And the NDT manufacturer’s is even more useless. We would be seriously under dosed.

      There aren’t that many people on T3 mono in the groups. I know that 40 mcg is considered a minimum dose. Which makes sense, seeing as we produce app 30 mgs ourselves in 24 hours. And our uptake is far from 100%. I believe the highest dose I have seen, is 85 mcg. I would join a T3 FB group, and also have a look at Paul Robinson’s site. And take my pulse several times during the day in the beginning. For me, pulse is the most reliable indicator of my thyroid levels.

      All the best, Liv

  3. Julia Sarah Weiss

    Hello this is super helpful! Thank you so so much.

    I was wondering if you have any tips on how to switch from NDT T3,4 to Synthetic T3,4?

    Thank you so much again!

    • L S-L

      Hi Julia!

      So glad to hear it. What you need to keep in mind, is that the synthetic is more potent than the NDT. So most people need to reduce their dose a little. If you take 180 mg Armour i.e., which contains 38 mcg T4 and 9 mcg T3. That would be 114 mcg T4 and 27 mcg T3. I would start out with 100 mcg T4 and 20 mcg T3. Of course, it all depends if you are optimal on your current NDT dose. I write about optimal thyroid levels here. Other NDTs may contain less hormone, so have a look at the content of your NDT.

      If you do like me, and follow your body temperature and pulse, you can easily adjust your dose. You find info on that on the same post.

      All the best, Liv

      • J Weiss

        That’s great tips, I’m just getting my free‘s checked and will get a thermometer now!

        Thank you again for all your help!

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