I'm hypothyroid (Hashimoto's) and currently experimenting with 15 mcg of Slow Release T3 (SR T3) together with 150 mcg T4. Note that my absorption is not the best, so 150 mcg T4 puts me around midrange of FT4.
I know on this forum it is recommended to wait 24 hours between the last dose of T4 and blood test i.e. take it one morning, then the next morning do the blood test on empty stomach and no hormones. With normal/pure T3 8-12 hours is recommended, which would mean taking it in the evening if the test is in the morning (2 hours after last meal and 1 hour before the next).
Slow Release T3 is different as the dose does not get absorbed at once, it keeps releasing small doses of T3 throughout the day. My theory is that I should wait 24 hours (just like with T4) between the last dose and blood test. This is to make sure the slow continuous releases have stopped as much as possible. If I test after 8-12 hours, FT3 is likely to be elevated as more T3 is coming in still.
My question to those with experience with Slow Release T3, what is the most correct thing to do here?
Written by
ak_83
To view profiles and participate in discussions please or .
I have not taken slow release T3 and hopefully someone else has but...
Do you know if it takes 24 hours for complete dissolution? If it takes 24 hours the amount at any given time should be the same, shouldn't it? It might be sensible to take it 12 hours before.... as after 24 hours there may be nothing to test.
I don't know about complete dissolution. I believe it is highly dependent on absorption, food type, transmission time etc.
T3 has a 24 hour half life, so every one of those small doses throughout the day will have that. Logically there is something to test.
Besides, as I understand it, even if it was pure T3, it does need to accummulate. You take one dose on day 1, the next day (day 2) you have 0.5 of it left in your body. You take another dose, so the day after that (day 3) you have 1.5 / 2 = 0.75 left. On day 4 you have 1.75/2 = 0.875. So what I'm saying is that even if you test pure T3 after 24 hours it still would show a reasonable result, albeit without today's dose degraded by 1/4 half life.
Unfortunately, slow release is just that - for most medicines. The release is slowed down but it isn't made even. They might try very hard. It might get quite a long way towards that. It might be good enough for the purpose. But it will still have some peaks and troughs - even if much less pronounced than otherwise.
Unlike with immediate release, we might not even know when those peaks and troughs occur.
Plus, when T4 is taken, there would usually be a T3 peak around 48 hours after taking it.
I do NOT know what would be best when taking slow release T3 - with or without T4.
This is very interesting as my doctor when I lived in London ordered my ST3 from Germany and thought that the ST3 lasted between 4-6 hours. My current thyroid doctor gets my ST3 from a lab in Israel and also reckons on it lasting about 4-6 hours. Neither lab would answer a question regarding the time that the ST3 was active. I have currently been prescribed 3 ST3 of 5mcg each to be spaced over the day. Have you or any of your other readers have any other recent published papers on ST3??
I don't know how long it will last in you, nor how evenly it will be released. And it might well be adequately smooth. But how to measure Free T3 in someone taking such products? I really don't think we have sufficient information to be clear.
Possibly the best answer would be multiple tests? (Yes, I know, the cost...)
Kinetic Analysis of Drug Release from Compounded Slow-release Capsules of Liothyronine Sodium (T3).
I meant to include the thought that slow release T3 might very well not be equivalent, dose-wise, to immediate release T3.
The slow release agents used might reduce how much T3 can be absorbed - let us imagine that immediate release is well absorbed and you get 90%, whereas with slow release, some simply doesn't get separated from the slow release agent meaning only 70% gets absorbed. (These numbers are just for illustration and don't represent any real products.)
Yes, the dose that I calculated (as a part of my NDT) of T3 and that I now take as SR T3 definitely seems quite low as well as possibly not releasing when I want. I'm pretty sure I'll try to last enough weeks for the blood test (along with symptoms) to be meaningful. After that I'll shift towards pure T3, all of it in the morning. But as it is, been 3 weeks and I'm pretty miserable on SR T3. Difficult to get up in the morning, difficult to get to sleep. No energy etc. Much worse than NDT was (and that was far from great already).
I thought on this forum I kept seeing 24 hours. helvella , what is the word amongst admins on this? 12 hours would be a drastically shorter half life indeed!
Wait, I'm confused. I thought T4's half life was 5-7 days and T3's half life was 24 hours (1 day). How can it depend if T3 comes from T4 as opposed to taking pure T3?
In my sitation it is a combination of T4 + SR T3, later switching to T4 + pure T3,
And the half-life of levothyroxine is around a week.
I take T4 only. When I take my tablet, I should expect to see a small peak of my T3 around 48 hours later. Of course, as I take my T4 every 4 hours, there is a complex overlapping of my dose yesterday, and the day before.
You take one dose on day 1, the next day (day 2) you have 0.5 of it left in your body.
Not 'in your body', no. The 24 hour half-life is in the blood. The T3 that gets into the cells lasts about 3 days. So, the maths is a lot more complicated than that, if you count both what is in the blood + what is in the cells = in the body.
The T3 that gets into the cells lasts about 3 days.
I haven't heard about this before hearing it from you on this forum. Is this something recent doctors have found out? My doc (I know she wasn't perfect) never mentioned anything like this nor did my elemental googling has ever unearthed it. So I'm curious about this leap in research - tell me more, please!
I have no idea if it's a recent discovery. It's something that diogenes told me in answer to a question. I can't tell you any more than that. But, I would think diogenes would be the one to know, if anyone would. I certainly wouldn't expect your GP to know a thing like that.
This is a bit of a red herring. You cannot say that a given number of molecules of T3 stay in a cell for n days. The whole body system is fluid, with T3 moving in and out of cells and into and out of the circulation. So in fact the T3 is always there, but you can't describe it in terms of a given bag of molecules held within the cell. It doesn't work like that - think of the body as a huge dynamic exchange between all the tissues and circulation.
I'm afraid it is trial and error. There is no way of advising a patient in detail, and expecting instant success. The only way is to gently change dose and see what happens.
I take only slow release T3 and the only advice I got from my doctor was to take it consistently at the same time every day, which gave him a point for comparison over time.
I was hoping to see a similar post as I take thyroid S which is said to be slow release. I take 1.75 on two days and 1.5 on the third but when tested I do the same as what I did just taking T4. So my readings are goo and I feel very well and for that reason I’ve never even tried splitting my dose. When I first stated my thyroid journey I was put on NDT by the NHS and again followed the same etc but never tested back then as was told my body only took what it needed so when one grain started to bring back symptoms I was moved up to 2 grains. I can’t do that with Thyroid S as it doesn’t work like that and I feel the same whatever the time of day or night it is. I don’t get any signs of being over or under medicated and I and the hospital are happy with my results.
So if anyone else takes Thyroid S and has comments I should be interested to hear from them. I started my present regime of Thyroid S over 5 years ago now so it’s not a recent change. My only issue is my consultant is still telling my GP we must raise my TSH! I just ignore her!
Content on HealthUnlocked does not replace the relationship between you and doctors or other healthcare professionals nor the advice you receive from them.
Never delay seeking advice or dialling emergency services because of something that you have read on HealthUnlocked.
Is anyone else taking slow release T3?
Update in sustained release T3 and new paper
blood test and T3 dose
