Sustained Release T3 (SR T3): Should you use this thyroid medication?

Sustained Release T3 (SR T3): Should you use this thyroid medication?

What is Sustained Release T3?

You probably already know that T3 is the single most important thyroid hormone in your body

If you've spent any time researching then you probably ALSO know that you can take T3 as a medication and that MOST thyroid medications contain only T4

But what you may not be aware of is that there are several different TYPES of T3 medications. 

And the one we are going to focus on today is known as sustained release T3. 

If you have sluggish thyroid function, for any reason, you should be aware of this medication. 


Because using T3 (in any form) bypasses the normal thyroid conversion process and provides your body DIRECTLY with the T3 that it needs to function. 

Sustained release T3 (abbreviated as SR T3 in this post and elsewhere on the web) refers to a special type of thyroid medication. 

SR T3 is bound to a specific ingredient which delays its absorption in your intestinal tract and provides a slow and steady absorption of T3 throughout the day. 

And this delayed absorption matters quite a bit (for some) which is what we will be talking about today. 

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Sustained Release T3 vs Immediate Release T3

But first, you should understand the difference between immediate release T3 (referred to as IR T3) and sustained release T3 (SR T3). 

Believe it or not, we really don't have standard nomenclature for the various types of T3 which are available (probably because many doctors are afraid to use either). 

For purposes of this article, and just to set the record straight, I've split up the types of T3 available into 2 groups:

  • Immediate release T3 (includes Cytomel and liothyronine)
  • Sustained release T3 (includes sustained release T3 by a compounding pharmacy)

That's it! 

There are really only two groups and 3 types of T3 medications. 

Yes, there are other medications which contain T3 in them but here we are talking about PURE T3 or T3 only thyroid medications. 

For this discussion, we are going to focus primarily on sustained release T3 but I want you to at least be aware that there are other types of pure T3 medications. 

You can learn more about immediate release T3 (Cytomel and liothyronine) here. 

Multi Dosing T3 Throughout the Day

Many people have the belief that if you want to take T3, in any form, that you really need to be taking it multiple times throughout the day. 

Even though this idea makes logical sense, I completely disagree with it when it comes to practical application. 

The idea goes something like this:

T3 thyroid medications are rapidly absorbed and utilized by the body. 

T4, on the other hand, stays in your system for weeks and weeks whereas T3 stays in the body for only hours. 

If you want to keep your T3 levels high then you must take smaller doses more frequently throughout the day. 

This allows T3 levels to stay high. 

All of these statements are true but there's only one problem:

It doesn't really matter. 

The blood level of your T3 is not important. What we care about is whether or not that T3 is getting into your cells to activate nuclear receptors (1). 

And, it turns out, you don't really need to multi dose your medication throughout the day to get this stimulation. 

BUT... there is one reason you may want to multi dose throughout the day and that has to do with sensitivity to T3. 

Some people, for various reasons, are extremely sensitive to even small doses of T3. 

So if they take one large dose per day they may react with anxiety/tremors/jittery sensations, and so on. 

These people MAY benefit from multi dosing. 

How does SR T3 fit in?

SR T3 sort of takes this problem away by delaying the absorption of your T3 and normalizing it throughout the day. 

So even if you are taking one large dose in the morning, that dose isn't hitting your system all at once. 

Instead, you are getting a slow release throughout the day. 

I don't find it necessary in most cases to multi dose SR T3 though it may be necessary for IR T3. 

How do you get Sustained Release T3?

Sustained release T3 is unique among thyroid medications in that it can only be formulated and produced by a COMPOUNDING pharmacy. 

Compounding pharmacies are specialty pharmacies that can combine medications in specific ways, they can place medications in carriers that normal pharmacies can't, they can create cleaner versions of medications, they can adjust the dosing of medications, and so on. 

Basically, these pharmacies give you MUCH more control over the medications you are taking. 

And the only way to get SR T3 is through these types of pharmacies. 

natural thyroid supplements version 2

The reason is simple:

Immediate release formulations of T3 such as Cytomel (2) and liothyronine (3) come preprepared in terms of their inactive ingredients. 

And the only way to delay the absorption of the T3 found in these medications is to put them in a filler which DELAYS the absorption of the medication in your GI tract. 

This is typically done with ingredients such as methylcellulose. 

Methylcellulose is difficult to break down (4) by your intestinal tract which means that your intestines have a harder time getting to the medication found in the capsules/tablets you are taking. 

Who should use Sustained Release T3

I should point out that while I am a fan of SR T3 I typically prefer to use the immediate release version of T3 because I think they are more powerful and easier absorbed. 

Having said that, there are still certain types of people who do much better on SR T3 compared to the immediate release versions. 

If you fit into any of these categories then you are likely someone who would benefit from SR T3: 

  • People who have heart palpitations when taking T3 medications
  • People who experience a jittery sensation or anxiety while using IR T3
  • People who experience an elevated heart rate or elevated blood pressure when taking IR T3
  • People who experience anxiety while using IR T3
  • Those people who don't have a schedule which permits multiple doses of T3 per day
  • Patients who do NOT have intestinal issues or absorption issues with other thyroid medications
  • People who are interested in weight loss (not specific to SR T3 but it's still an option)
  • People who have experienced abdominal PAIN (or ulcers) with IR T3
  • People who get headaches with IR T3
  • People who have tried and failed IR T3 for pretty much any reason

I can probably simplify this list by saying that if you have failed IR T3 for any reason you may want to try SR T3. 

You would be surprised at how many people tolerate SR T3 compared to those who do not tolerate IR T3. 

The reasons can be endless, but I've listed several above. 

Also, you don't always need to start with IR T3 before swapping over to SR T3. 

It's perfectly fine and safe to start with SR T3 if that is your preference. 

Downsides of using SR T3

There aren't many downsides to using SR T3 compared to more immediate release version. 

Perhaps the main downside is that in order to get a 'sustained release' version of T3 it must be bound to something that is somewhat hard for your intestines to break down. 

What this does is act to REDUCE or SLOW DOWN absorption in your intestinal tract. 

What ends up happening, though, is that certain individuals have a much more difficult time compared to others in breaking down the medication. 

The variability in breaking down the binding materials leads to variability in absorption. 

What does that mean to you?

It means that it can really be difficult to nail down your dose. 

It also means that you can't really switch from immediate release T3 to sustained release T3 in a milligram to milligram conversion. 

The absorption variability can be as much as 50% in some cases. 

Let's use an example to drive this home:

Let's say that you are currently using something like 10 mcg of Cytomel or liothyronine. 

It's working well for you but you are experiencing heart palpitations so you want to try and get SR T3. 

Can you just switch over from 10 mcg of Cytomel to 10 mcg of SR T3? 

Typically not. 

Instead, you may need as much as 20mcg of sustained release T3 to ensure that you are getting the same 10 mcg dose you were getting before. 

This is because your intestinal tract may not be able to break down the binding materials which hold onto the T3 ingredient. 

Ultimately, you may lose some of that T3 in your stool without it ever being absorbed. 

This is probably the single biggest downside. 

Another downside has to do with the cost of the medication and the fact that it can only be obtained from a compounding pharmacy. 

You will NOT be able to walk into a CVS or Walgreens to get sustained release T3. 

Instead, you will need to have the medication specially prepared by a compounding pharmacy which means you may have to do the legwork to FIND that pharmacy as well as a physician who is willing to prescribe SR T3. 

These are really only minor downsides, though, when you look at the bigger picture. 

SR T3 is far more beneficial than it is harmful and is typically easier to dose compared to immediate release version of T3. 

Final Thoughts

Sustained release T3 is a great T3 only thyroid medication which provides a ton of benefit for thyroid patients. 

I believe that MOST thyroid patients do better when they include some T3 in their thyroid medication regimen. 

This doesn't mean you need to take ONLY T3 (and leave out the T4), though that is an option, but instead that you may benefit by ADDING T3 to your existing medications. 

You can combine SR T3 with your existing levothyroxine/Synthroid dose to obtain the benefits that T3 thyroid hormone provides. 

Now I want to hear from you:

Are you currently using SR T3? 

If so, why are you using it? Did you experience problems with IR T3?

If you are using it, what benefits have you noticed? What side effects have you noticed?

If you are considering using it explain why!

Leave your comments or questions below! 

References (Click to Expand)

sustained release t3 vs immediate release t3
Dr. Westin Childs

Dr. Westin Childs is a Doctor of Osteopathic Medicine. He provides well-researched actionable information about hormone-related disorders and formulates supplements to treat these disorders. He is trained in Internal Medicine, Functional Medicine, and Integrative Medicine. His focus is on managing thyroid disorders, weight loss resistance, and other sex hormone imbalances. You can read more about his own personal journey here.

42 thoughts on “Sustained Release T3 (SR T3): Should you use this thyroid medication?”

  1. Dr Childs,

    Can you please do a dedicated post on Histamines and Estrogen/Progesterone/Testosterone imbalances? It was a big underlying issue for me and looks like very little information out there about what to do!


  2. i am on Synthroid 75mg and t3 5,she put me on the t3 because i was not focusing and not remembering much and just foggy.. all through the day. i am also having a lot of fluid retention ,and weight gain do you have any suggestions.

  3. Hi, Dr. Childs,

    I’m taking T3 SR 1.5 mcg twice per day and 25 mcg of Levoxyl once per day. Feel lots of hypo symptoms such as fatigue, hair loss, mild depression, and shortness of breath (not cardiac related, checked out OK). In addition I have heart palps. About 18 months ago I was on 1 grain of Naturethroid, but then that stopped working for me, so my doc is trying me on this regime (about one year now). He says my labs are OK, but they are all on the very low end of the range, except TSH, which is 3.65. Any thoughts? Thank you for doing what you do.

  4. Hello,
    I take a SRT3 from Wellness compounding pharmacy in addition to non generic synthroid 125mg and have done this for a good year. I had previously taken the SR T3 under the Wilson program, but had swelling and Achilles heel issues (that disappeared when I stopped)

    It has been working really well and I was gradually dropping some weight until this past Christmas- not sure what happened-I made some dietary changes (less sugars, GF) after putting on 4 pounds.
    And now my free,T4 and Free T3 are high according to your optimal math equations and TSH is non existent and no weight loss.
    So actually not sure–too much of everything?? I’ve got a great PC Dr. who listens and experiments with me but isn’t a thyroid expert.

  5. When taking both T4 and T3, does the T3 stop the conversion of the T4? I am on .125 of T4 and 15mcg of SR T3, and feel a bit hypo (I usually take .137 of T4). I was reading your article about SR T3 and that if a person was to convert from IR T3 to SR T3 that they would most likely need 20mcg of SR T3 if they were taking 10mcg of IR T3. So, in regards to your conversion chart, how much SR T3 would replace 12.5 of T4? I apologize for being a little all over the place, just trying to understand. Thank you

  6. Hello Dr. Childs,

    I started Cytomel 5 mcg along with my Synthroid. I want to take them all together early in the morning with plenty of time before breakfast. My question is, if I take the Cytomel that early will the effects last long enough throughout the day? I don’t want or need to multi-dose the Cytomel. I just want to crash later in the day because the T3 has worn off. Thank you!

  7. Why are doctors prescribing Armour more than anything else recently. Can I raise my Armour to get more T3

  8. Hello;
    Do you have recommendations since antibodies are the only thing that is high? I am on Armour Thyroid now.

  9. Hi Dr. Childs,
    I am taking Synthroid 125mcg one day and then I take Synthroid 112mcg the next day. I alternate these two doses per my Endroconoligist. I also ordered your Leptin and am taking 1/2 hour after my Synthroid. I see my Endroconoligist Thurs July 2nd for him to check my goiter (not big and has gone down). Should I suggest that he do any certian tests while I am there?

    Thank you.

  10. Hello! I was diagnosed with Hashimoto’s in 1990 and put on Synthroid which never worked for me. After some time a very small amount of Cytomel was added without much affect. After 12 years I was diagnosed with Papillary Thyroid Cancer and had a total thyroidectomy in 2002. I developed neuropathy in my feet after my thyroid was removed but when I had to transition off of Synthroid and on Cytomel to get a radioactive test, my feet stopped hurting so I realized it was Synthroid that was hurting me. At this time I sought out the help of a naturopath and shifted away from an endocrinologist. Armour caused neuropathy in my feet again but SR T3 worked like a charm. I have been on it for about 17 years. The problem for me is that if my dose is a little too low, in time (say 3 months) I will be too low and will have trouble with having a BM. On the other hand if my dose is a little too high, again in about 3 months I may experience some heart palpitations. In other words SR T3 seems to act like a ‘runaway train’ and eventually it’ll become too low or too high. Is there a way to stabilize it? I also have had naturopaths tell me how our bodies also benefit from having T4 (I believe I was told the brain benefits from T3 and the stomach or GI tract benefit from T4). But when I have tried to decrease SR T3 and add in T4 (also compounded) I cannot tolerate T4 at all. Do you have any suggestions or comments?

  11. I take 75 mg of np thyroid which has the T3 in it. How do you know if it is enough, I get such muscle weak ness after I tried a t3 booster I had to stop. But I had so much energy, Just not sure what to take anymore, plus started on Zoloft for the depression. Can you just take t3 alone with out the T4 been on this roller coaster for over 20 years, would like some help.

  12. Dear Dr. Childs, I am using T3 – Thybon Hennning from Sanofi, Germany. I dont know if its SR og IR, but this is the only T3 I can use. Liothyronine was no good for me! I use 20 mcg Thybon together with only 45 mg Armour Thyroid. I have used this combination this last year – and I have got my life back! I have celiac disease and other digestion challenges, but this combination got me back on track! But now my doctor will no longer prescribe T3, so I have to get another doctor – again.
    I dont know if this new doctor will help me -yet.
    In Norway it is sooo difficult to find a good thyroid doctor!
    I have said it before; I wish we had doctors like you!!!

  13. I’m a little confused about the article itself. If we want this, what exactly are we supposed to ask for from a doctor? I have a doctor that would likely prescribe me it but she’s no thyroid specialist so she’s unlikely to know exactly what it is. So it seems like you’d need to have a doctor who knows how to prescribe it?

    I’m currently on Armour Thyroid, no Hashimoto’s, and my insurance doesn’t cover it so I haven’t had it in a week, and they only cover NP Thyroid. I’m starting to question on if I need medication anyway. Plus, I had been getting really high heart rates so my PCP started lowering my dose anyway. In my case, no one knows why I need it but my genetics do show a lot of potential for interference with my thyroid. I had been taking it since probably 2011 or so off and in but haven’t been able to keep a steady doctor that I feel really knows how to treat me. Labs are easy enough for me to get, now but interpreting them is still difficult even with all my research.

    This ended up being a venting comment, but feeling a little frustrated with not knowing where to go in terms of medication, or even if my thyroid is even a problem.

    • Hi Jeanine,

      Yes, you would probably need to have a doctor who has prescribed it before. This has to be made in a compounding pharmacy which is not a regular pharmacy like a CVS or Walgreens. Most regular doctors do not use these types of pharmacies or even know they exist.

  14. Dr. Childs, been following you for many years and appreciate your information and love the podcasts. Do you do any telephone “appointments” where I could ask you the many questions I have. I am a 65 year old woman, diagnosed at age 18 hypothyroid. I have always struggled with symptoms. I am small, light, and very active, with a solid nutrition plan. I have questions about my labs, and medications which rite now are Synthroid 112, and Liothyronine 25. You may answer here or email me. thanks

  15. Was taking 20mg of Cytomel in regular T3 and after much research and reading, I heard that SR T3 would be in my body and released throughout the day and help with my energy level. I have a doctor and a compound pharmacy that had no problem with prescribing it or making it. I do have a question though. I was on 20mg of regular T3 and went to 20mg of SR T3, should that SR T3 been 40mg based on what I just read? If you think so I would like to discuss with my doctor.

  16. I switched from .125 mcg Synthroid to Armour a bit more than 2 years ago. My doctor started me on 60mg a day but I was so tired I could hardly move. She then upped it to 75 mg but as I was still tired she upped it again to 90 mg. I felt somewhat better on 90 but still tended to feel tired and to have a body temp of around 96 to 97.4. My doctor referred me to another more experienced doctor and she agreed to increase my Armour doseage to 125 mg and I have been on that dose for about a year. While I generally feel good and run a body temp between 97.5 to 98.6F I am down to 134 pounds from the 144 lbs I weighed when I switched to Armour. As a Type 1 diabetic I follow a fairly strict low carb diet and if anything am more inactive today than when I switched to Armour. Could it be that taking an excessive amount of Armour is causing the weight loss?

  17. Hi Dr. Childs,
    I’ve been on Armour Thyroid for ten years. I was taking it in the morning, now I take it at night. Feel pretty good, but sometimes I wake up at night with shortness of breath. I would like to lose ten pounds, I’m 5’ 5” and weigh 136., And that’s in the past year, normally I weigh 124. I thought this is why I have shortness of breath. My PCP checked me out, no heart issues. Any suggestions? I had a biopsy on my thyroid because I have goiter at my check up in Feb. all good. Also is Armour Thyroid T3 and T4? I take 60 mgs. and have the entire ten years.
    Thank you!

  18. Greetings Dr Childs,

    My doctor has prescribed both T4 and T3 medication and I am happy with the added benefit of the Cytomel. My question is this….. is the ratio of the two medications of importance? I know that I feel much better after my recent t3 Medication increase but are there limits to the amount of t3 medication one can use daily?


  19. Dr. Childs,

    Since I’m euthyroid (but symptomatic with high antibodies) my endocrinologist has only given me 15mg. of levothyroxine and remarked it probably won’t make much of a difference. Well, it hasn’t made a difference and so I asked if I might have a conversion problem and what about some T3?

    She said she couldn’t give me any T3 because my levothyroxine dose was too small. I did eventually get her to switch to NP Thyroid because I know there is a small amount of T3 in glandulars. (At 15mg. of NP it still isn’t making much of a difference).

    Is this really true that one cannot give someone T3 when they are on such a small dose of T4, because as she says, it will mess up the ratios? I know you can’t read her mind, but what rationale might she have for saying this?

    You will probably say that I need to get a full range of testing, but since I’m already taking medicine, she will only get TSH. Do I need to get T3 and RT3 tests? (Really, should I try to find a different endocrinologist?)

    Thank you,

    P.S. If you cannot answer the above questions, I got the results of a nighttime saliva cortisol test, on two successive nights. One was 30 and the other 60 with ‘normal’ being less than 100. Are my results high normal or low normal? What is optimal? Thank you again.

  20. Hi
    I have subclinical hypothyroidism. I’m currently in 20 mg IR Cytomel which seems to balance out my levels. I do have restlessness and some anxiety. I am 70 years old. I see a DO who seems very thorough with thyroid. Am wondering if I should try SR Cytomel? Also I have very low hormone levels including progesterone, estrogen and testosterone. Doc thinks I should try pregnenolone and progesterone. What do you think? I sleep pretty good now but s am taking some homeopathic relaxant which helps with sleep. Thanks for your input. Char

  21. I started on Armour in 1993 with decent success. In 2002 I read about Wilson Syndrome, and shared the book with my D.O. so we could try cycling T3. I don’t know why I was never able to get my thyroid to work on its own again. I’ve always tested negative for Hoshimotos’s. Since I had IBS back then, SR-T3 dosing was all over the place until 2003 when I eliminated gluten and offending foods. I was fine on 15mcg BID for a few years, and then we decided to add a bit of T4 to balance things out (like getting cold and sleepy when the T3 ran out). Over the years, only the T4 has been tweaked as my weight changed or I’ve had symptoms: 50mcg, 75mcg, 100mcg, 125mcg, and now 112mcg. Last year, however, I started keto and dropped 24 pounds. I had to adjust the SR-T3 up to 20mcg BID. I’ve since just been doing LCHF with about 45-70grams of carbs a day (not real keto). My most recent labs were flagged as low in thyroixine (bound I assume since free was low normal), but this was the first time I ever avoided biotin for a few days before testing. My RT3 is only 12.1. (Back in 2002 it was 80.) It has been a constant battle with doctors to get this stuff prescribed, as no one seems to definitely know what tests to order, how to interpret these tests, and to prescribe combos of medications. I’m just a squeaky wheel, so they humor me and order what I ask for. I am curious as to what a normal physiological dose might be for T3 and T4 in a 125 pound female as my thyroid has pretty much been retired for years.

  22. Hi Dr. Childs,
    This is Mari Trejo. I have been taking 50 MCG tablet of Levothyroxine for the past 7-10 years, but have not been successful with it. Am taking some supplements to enhance the thyroid medicine with some luck. Now my practitioner order NP Thyroid 15 MG. Could you give me more less an approximate good dose for NP Thyroid. Some years ago, I was taking the original Armour Thyroid, but had very bad experience. Thank you so much.

  23. I am 52 and on HRT. I’ve had crushing, debilitating fatigue and brain fog for a few years. No weight gain. I eat a varied, healthy diet. I exercise, but not too vigorously. I sleep 7-8 hours, generally. I started 5mcg of Liothyronine in Oct 2019. Tried both SR and IR and couldn’t decide which I preferred. Ended up doing SR twice a week and IR the rest of the time (is that okay?). Felt a little better for a few months, but then was just as tired as ever. When I got my labs done 8 months later my Free T3 was even lower and my Free/Rvs ratio worse. So I went up to 10 mcg. That didn’t cut through my fatigue so now I’m up to 15 mcg IR in divided doses. Having dizziness, elevated heart rate and shakiness, so tried a morning dose of 15 mcg SR which felt much better but then I couldn’t sleep because I wasn’t tired enough. Might I be better off with just a thyroid supporting supplement? I’ve been tested for all kinds of things and can’t find an underlying condition.

    July 2019
    TSH – .69
    T3 Total – 84 NG/DL
    T4 (thyroxine) – 6.9 UG/DL
    Free T4 – 1.04 NG/DL

    ESR (sed rate) – 6 mm/Hr.
    Ferritin – 71 ng/mL

    October 2019

    TP antibodies – <1
    Free T3/Rvs T3 ratio 1.98
    Free T3 250
    Reverse T3 126

    October 2019 – Began 5mcg Liothyronine


    TSH – 0.77
    Free T4 – 0.8
    Free T3/Rvs T3 ratio 1.88
    Free T3 – 220

    June 2020 – Began 15mcg Liothyronine

  24. Hello! Thank you for all the information. I want T3…. can you please help me? I live in Canada…
    I had a Thyroid removal at 25 yrs old and since then all I do is gain weight…. I used to be an athlete… the worst thing I ever did in my life was agree to have it removed.
    Anyways I’m on synthroids 175 mcg…. According to all your explanations, T3 could really help me. A prescription is mandatory? Can we order it from you?

  25. Hi there,
    I have had every combination of thyroid meds! Originally, my TSH was normal, and my thyroid was always fine, but my T3 numbers were well under range (T4 slightly). We recently cut out all t4 (have done that before) and went back to all t3. I was taking all Cytomel, but am slowly transitioning to the SRT3 and adjusting. I didn’t want to completely switch over at once, as I’ve read about needing more of the slow release, and my doctor is very conservative in starting at low amounts and adding every 6-8 weeks.
    My question is – what is the half-life of the SRT3? Does it release over 24 hours? 12 hours? I’ve read mixed opinions on if it should be taken once a day or twice a day (ever 12 hours) and my doctor doesn’t appear to know for sure.

  26. Nature throid is on recall once again leaving me in a panic as it is the only thyroid med that worked for me. After reading about sustained release T3 from another of Dr. Westin’s blogs, I called my doctor and asked if we could go the compound route. He was very supportive and said that it should work well for me and that it would be wonderful if I got off the recall issues we were having with the Nature throid.
    I feel amazing since the switch. No more heart palps or jitters. It was strange at first not having the T3 dump in the morning but it is so nice to just go along on an even keel all day. Only issue I’m having is about 6 pm I start to feel the low thyroid symptoms so after having a blood test done at 6 pm to see where my levels are- we are going to add a low dose around 6:30.


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