Slow-Release versus Pure T3 (Standard T3)

From time to time a thyroid patient may ask 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 and 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

If only a tiny amount of extra T3 is required, then 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 meds), there are two goals:

a) to avoid causing hyperthyroidism in any of the different tissues of the body due to too much T3


b) to use enough T3 to overcome the cellular issues which have caused the problems in the first place.

To achieve these  two goals different amounts of T3 will be needed at different times of the day. Most people using standard T3 need different sized divided doses to provide only as much T3 at any given time as is required. 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.

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.

T3 for CT3M Use

For the circadian T3 method (CT3M) there is no question that standard T3 swallowed in one go is the only sensible way to implement it. CT3M needs the entire circadian T3 dose to be absorbed in one go and as quickly as possible. We want the entire T3 dose to reach the pituitary gland as fast as possible, and we want to be able to titrate the dose size and timing and 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)