Slow Release Versus Standard T3 for Thyroid Patient Treatment

From time to time a thyroid patient may ask me whether slow release T3 or standard T3 (pure T3) should be used for T3 replacement. Slow-release T3 is sometimes referred to as sustained-release T3.

There are really two parts to this question:

  1. Is standard T3 or slow-release T3 best in general for T3 replacement?

  2. Which is best for the circadian T3 method (CT3M)?

Let me answer this by dealing with the general use of T3 separately from that of CT3M.

General Use of T3: Using T3 in the Daytime on Its Own or In Combination With T4 or NDT.

If only a tiny amount of extra T3 is required, some people can do well with slow-release T3, and others do better with standard T3, i.e. it would be a matter of trying the slow-release T3 and seeing how it worked.

For those people who need much more added T3 (without without any T4 medication), there are two goals:

  1. To avoid causing hyperthyroidism in any of the different tissues of the body due to too much T3, i.e. tissue over-stimulation.

  2. To use enough T3 to overcome the cellular issues that have caused the problems in the first place. This requires enough T3 to reach the thyroid receptors in the cell nuclei so that the genomic effect of T3 lasts for a long enough time to correct any hypothyroidism but is not too much to cause any hyperthyroidism symptoms. It does not matter whether the blood levels of T3 fluctuate – what matters is getting our cells to work well.

To achieve these two goals, different amounts of T3 may be needed at different times of the day. A lot of people using standard T3, need different sized divided doses at different times of the day. This is so that they receive only as much T3 at any given time as is required to ensure that it lasts long enough until the next T3 dose, but without causing any signs of over-stimulation.

With slow-release T3 it can be difficult to provide enough T3 without either having too much or too little. It is difficult for most people to find a slow-release dosage that achieves these goals so that they remain euthyroid at most times with no evidence of hyperthyroidism.

Some patients do find that slow-release T3 works for them though. Others find that they have to have the slow-release T3 compounded differently a few times, in order to find the optimum release rate for them. This process can be quite expensive.

For the thyroid patient who simply wants to add a small amount of T3 to a mostly T4 based regime, slow-release T3 may work well though.

T3 for Use in The Circadian T3 Method (CT3M)

For the CT3M, there is no question that standard T3 swallowed in one go is the best way to implement it.

CT3M needs the entire circadian T3 dose to be absorbed as quickly as possible. We want the entire T3 dose to reach the pituitary gland, as fast as possible. We also want to be able to titrate the dose size and the timing of the CT3M dose in order to try to control cortisol levels with as much sensitivity as possible. Slow-release T3 would provide none of this. The CT3M requires standard T3.

I hope this clarifies things for those that may not have been certain.

Best wishes,


(Updated in February 2019)

Paul Robinson

Paul Robinson is a British author and thyroid patient advocate. The focus of his books and work is on helping patients recover from hypothyroidism. Paul has accumulated a wealth of knowledge on thyroid and adrenal dysfunction and their treatment. His three books cover all of this.

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  1. monsie pickles on 3rd August 2020 at 8:20 pm

    I have a pituitary microadenoma. I do not convert T4 to T3. My rt3 is very high. I started taking compound 2.5 mcg T3. I am 82 years old.

    • Paul Robinson on 4th August 2020 at 9:53 am

      I hope your doctor is carefully monitoring you Monsie. He or she should keep an eye on your ECG if you’ve only just started this given your age. However, 2.5 mcg is very low indeed so it should be very safe.
      Take care,

  2. sarah on 15th August 2022 at 7:39 pm

    I am on sustained release T3 only twice per day and it worked great for almost 5 years. My FT3 labs were just above the top of the range at 4.0-6.0. Last year they went to 7.0 and my doc lowered my dose by 20% and now I am at 4.o but feel totally hypo. Is it possible to have higher blood FT3 but still have malabsorption due to the sustained release compounds?

    • Paul Robinson on 15th August 2022 at 7:56 pm

      Hi Sarah,

      Any T3 medication is incredibly variable in terms of how it shows up in lab test results. Even slow release varies a lot.

      I usually advise people to go more on symptoms and signs than FT3 lab test results. But if you test FT3 then you should only test it when it is at trough levels – which means not within a few hours of a dose. Ideally, 12 – 18 hours would give you trough readings. This, combined with using symptoms and signs to guide you plus my Recovering with T3 book for its wealth of information should be good enough.

      I’ll give you two blog posts to read in detail – pick out the relevant bits:

      Hope this helps.

      Best wishes, Paul

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