Thyroid UK
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Advice for adding T4 back in to T3 only?


I'm going to run out of Grossman Cynomel in about three months and I don't seem to be tolerating any of the other brands of T3 I can get hold of - they're giving me adrenaline surges.

I am contemplating adding some T4 back in - something I've been thinking about doing for a while anyway, as I suspect my conversion problem was nutritional (low magnesium) and is now fixed.

My reasoning is that if I add a bit of T4 back in I can stretch out my supply of T3 tablets for longer, until hopefully I can obtain a brand I do tolerate or Grossman start up production again.

I wonder if any of you have swapped from T3 only to T3/T4 combination and have any advice for making the change?

6 Replies

VitaminKgirl, How much T3 are you taking and how much T4 were you taking before you switched?

I've switched from T3 to T4 and back again several times and have been comfortable on T4+T3 combination for >18 months.


I'm taking 18.75mcg (3/4ths of a 25mcg tablet) of Grossman Cynomel.

When I was on T4 I was taking 87.5mcg and my TSH was as low as it could go.


VitaminKgirl, 18.75mcg T3 is equivalent to 56.25mcg T4. Try 62.5mcg T4 + 6.25mcg T3 which is equivalent to 81.25mg T4. You'll need to continue taking 18.75mcg for 6-7 days while the T4 is absorbed.


Have you thought of taking NDT instead


Hi vitaminKgirl, selenium is the main nutrient needed to convert T4 to T3, along with a little iodine/iodides and zinc. Magnesium, as you say also helps but make sure you have the required amounts of the other minerals otherwise if you're low or deficient your body won't be able to make this valuable conversion.

Getting the right type of selenium is also important. I'm presently trialling some 'selenium phosphate' because the selenium methionine I was using wasn't helping much. Don't rely soley on daily Brazil nuts either, as these haven't sorted my low selenium out. It depends on where the Brazil nuts are grown to the amount of selenium they contain. Unfortunately it doesn't state on the nut packaging the selenium content, so we don't know how much we are consuming.

Plenty of good organic cold pressed oils and no or little hydrogenated and trans fats, for cellular membrane function and cells to work properly. We so want to get that T3 into the mitochondria! :-)


Thanks for the thoughts everyone.

I was tested for selenium deficiency and was taking quite a bit with no change. I'm pretty sure the problem was magnesium, as it's also involved in T4 to T3 conversion and I later identified a clear deficiency. I was pushing vitamin D quite hard when I was taken ill, and increasing vitamin D can cause you to lose your magnesium.

It's reassuring to know others have successfully swapped between T3, T4 and a combination.

I have ordered some NDT to try. I have used it before but became intolerant of it at the same time as I became intolerant of T4, undoubtedly because it contains T4.

I know that my body does produce some T4 and that I can convert it to T3 based on recent experiences, so hopefully I can tolerate it again.


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