Thyroid Hormone Levels: T4, T3, T2, and T1

Your thyroid gland, which is situated in the lower front part of your neck, produces hormones that play a role in a variety of functions throughout the body, and impact many other hormones outside the thyroid. The two main states of dysfunction seen in thyroid conditions are called hyperthyroidism (too much hormone) and hypothyroidism (too little), and can be induced by a number of different individual thyroid disorders. There are many conditions involving this gland, each of which presents a unique pathology and characteristic clinical picture, usually seen when lab values for these hormones fall outside their normal ranges.

What hormones are made by the thyroid gland?

Of the several “thyroid hormones” produced by this gland, there are two that are clinically relevant. One is called thyroxine, also known as T4, while the other is named triiodothyronine, commonly referred to as T3. They are both heavily involved in energy management and a variety of biochemical and metabolic reactions and functions throughout the body. While T4 is more abundant in the bloodstream, it is T3 (which is derived from the conversion of T4 in the kidneys and liver) that possesses the most potency and is thus responsible for most metabolic activity. In the event that a patient requires supplementation because of low hormone levels, both forms are available therapeutically, and an endocrinologist will be able to explain which is needed and why.

What are the optimal levels of the main thyroid hormones?

The normal lab range of total T4 in adults is approximately 5-14 micrograms per deciliter (mcg/dL), while free (not bound to proteins) T4 is considered normal between 0.8–2.0 nanograms per deciliter (ng/dL). Total T3 should be between 80-200 ng/dL, and free T3 should remain within a range of 2.3–4.2 picograms per deciliter (pg/dL). However, optimal levels of any hormone are often debated and may differ from country to country, doctor to doctor, or institutionally.

What is the difference between “free” T3 and T4 and “total” T3 and T4?

Total T4 and T3 indicate the total amounts of these hormones produced by the thyroid gland, whereas free or “unbound” T4 and T3 measure the amounts of hormones that are bioactive, or actually available to your cells and tissues (typically less than 1% compared to the total produced). Looking at the free hormones usually gives a better clinical picture to the doctor, and is generally more helpful for diagnostic and treatment purposes.

What is TSH or thyroid-stimulating hormone?

TSH, also known as thyrotropin, is actually not a thyroid hormone; rather, it’s a pituitary hormone that stimulates the production of thyroid hormones. High levels of TSH may indicate that the body is hypothyroid, though there are other reasons for elevations, such as a primary pituitary tumor. The traditional reference range for TSH has been between 0.5 and 6.0 milli-international units per liter (mIU/L), although many endocrinologists now recommend that it remain between 0.3 and 3.0 mIU/L. However, if the upper portion of the normal range were lowered to just 3.0, approximately 20% of the population would be considered hypothyroid, instead of about 5% now. TSH levels outside the normal range may be associated with a number of disease states.

What are T2, T1 and calcitonin and why doesn’t my doctor measure those?

T2 and T1 are thought to play minor roles in the thyroid and rest of the body, primarily serving as precursors to and byproducts of T4/T3 formation. They may be more involved in thyroid function, but as far as we can tell right now, they have little impact beyond that noted. Calcitonin is a thyroid hormone that, along with parathyroid hormone (PTH), regulates calcium, and it is another measure that can be too low with hypothyroidism.

T2 and T1 aren’t measured because they have no demonstrated clinical value. Calcitonin is sometimes measured as part of an “extended thyroid panel”, when trying to settle on a definitive diagnosis where none is clear, especially in the cases of some suspected endocrine tumors. Values for the latter are considered normal below 10 pg/mL in men and 5 pg/mL in women. Unlike the standard medical treatments for hypothyroidism, desiccated thyroid supplements often contain T1, T2, T3, T4 and calcitonin.

Questions for your doctor:

  • Why do different doctors use different measurements for the “normal” ranges of thyroid hormones?
  • What are the benefits and are there any risks of taking desiccated thyroid products?
  • Is a TSH test diagnostic of hypothyroidism by itself?



This post contains opinions of the author. is not a medical practice and does not provide medical advice, diagnosis, or treatment.  It is your responsibility to seek diagnosis, treatment, and advice from qualified providers based on your condition and particular circumstances.  Camino Real Ventures, Inc., the company that makes available to you, does not endorse nor recommend any products, practices, treatment methods, tests, physicians, service providers, procedures, clinical trials, opinions or information available on this website.  Your use of the website is subject to our Terms of Use and Privacy Policy


  1. I have been diagnosed with over active thyroid. I was told that my T1 level was high. I generaly feel tired, losing my hair and so on. What is the best action to take? the doctor sugested raioactive iodine and meds for life. I feel lost and like doing nothing about my problem and just letting the thyroid run its course. If I take the doctors advise will I feel better? I don’t my symptoms to go away I want to be cured.

    • Over active thyroid would involve more abnormal results than an elevated T1. You need to talk to your doc, or get a second opinion. If you can stand it wait a while, as long as your heart isn’t being affected by hyperthyroidism or graves disease. Sometimes, although it can take years of hell, things can settle down. But in the end, most people never feel well again, no matter which route they choose. All the best to you..!

  2. I just don’t want my symtoms to go away I want to be cured

    • Katie Cleary says:

      Hi Sam, I’m so sorry you are dealing with hyperthyroid. I know it is so frustrating. If you have Graves’ Disease, the doctor’s recommendations are usually standard treatments from what I know of hyperthyroid. It may also be the case that you will be hyperthyroid for a while and then switch to hypothyroid, which is common with Hashimoto’s (which is the condition I live with). From what I know symptoms can be treated, but thyroid disease cannot be cured as of today. But there is research ongoing, and fingers crossed there will one day be a cure. I know you wrote this a while back, but I just wanted to say that I sympathize with what you are going through and hope things are better today.

  3. There is no such thing as t1and t2. Your reference page mentions nothing bat these “hormones” please stop filling people heads with false information. If I am wrong and you have medical documents to support it please share.

  4. diagnosed with hypothyroidism. each month t3 t4 increased due to dry skin,
    hair and other symptoms, now t3 40mg & t4 105mg, still feel same, what
    should I ask my doctor? Also elevated homocyteine and leptin and inflam-mation. Any suggestions I would greatly appreciate.

    • Katie Cleary says:

      Hi Judi, I’m the founder of this site and I too have hypothyroidism (Hashimoto’s). One of the reasons we wrote this post is that natural thyroid medication, such as Armour and NatureThroid, includes all four thyroid hormones – T4, T3, T2, T1. If our body made enough thyroid hormone, it would be making all four, yet the synthetic hormones only replace T4 and T3. I’m not a doctor so please don’t take this as medical advice, but there are many advocates out there that believe natural hormone replacement will relieve symptoms better than synthetic. I think it varies person to person, but I have had much better luck on Armour than I did on Synthroid (see Stop The Thyroid Madness website for more info on this). I’m not sure about the other part of your question, but I would be happy to post it to the Facebook AutoimmuneMom page if you want and can report back – let me know! Thanks and take good care, Katie

      • Alan Inselberg, C.C.N. says:

        Hi Katie, I am a Certified Clinical Nutritionist who was mentored in the use of Iodine by Dr. David Brownstein, M.D. I specialize in the restoration of the Thyroid and the use of Iodine, which along with the Amino Acid Tyrosine is essential in producing Thyroid Hormone. I have reversed Hashimoto’s Disease in 4 patients. As time permits I offer my professional advice for free to help Mankind and keep them from the clutches of Big Pharma. I teach individuals how to heal themselves so they don’t become anyone’s patient for the rest of their life. I do this solely with a change in a person’s Nutrition profile that includes a lifestyle change in their food choices. I happened across your site quite by accident while researching where to purchase a bio-identical T2 Thyroid Hormone, which is the primary Thyroid Hormone to assist in weight loss. For your reference, a normally functioning Thyroid will produce 80% of T4, which is a storage hormone; 16% of T3, which is the energy Hormone; and 4% of T2 & T1, and less than 1/2% of Calcitonin, the Hormone used to help regulate Calcium. May I suggest that you become greater informed about the significance of Iodine and why you can not live without it from a video lecture by Dr. David Brownstein at this link “!” It was a lecture done at the American Nutrition Association in 2011. I would also suggest Dr. Jorge Flechas, M.D. videos “Iodine & Cancer” and “Iodine, Whole Body Sufficiency” Dr. Jorge Flechas, MD and Dr. Guy Abraham, MD were Dr. Brownstein’s mentors in the use of Iodine. Once you have seen these videos and desire more information I will be delighted to advise you how to get rid of your Hashimoto’s Disease and all of your Hypothroid symptoms for good. And then you can, from your own personal experience, help many hundreds if not thousands of others with the same or similar problems. Your site can grow like my friend Lynne Farrow who found Dr. Brownstein’s information and cured her Stage 3 Breast Cancer using Iodine, and created a site to empower other Women that they too have another choice. Her site is entitled “” Ms. Farrow also wrote a book called “The Iodine Crises” The forward of the book was written by Dr. Brownstein. As a general rule you should never need to supplement any Thyroid Hormone if you still have a Thyroid. Whether you have a Thyroid or not you still need to ingest Iodine because other tissue, such as the Ovarian Follicle also make Thyroid Hormone just like the Thyroid itself. You may email me for more info if you desire at “[email protected]

  5. Marcia Parr says:

    I was diagnosed with polymyalgia in 2000. I was on prednisone for 4 1/2 years. My hair started falling out slowly. now I have lost over half of my hair. It falls out on floor and I can feel it falling on my shoulders. I have been on T3 for over a year. Not any better. I have had blood work a couple of weeks ago , Came back normal. I have requested a printout of results. Do I need to have T1 T2 checked? I am at a loss. Thank you,

    • Katie Cleary says:

      Hi Marcia, thanks so much for your comment – I am sort of at a loss as to how to answer you though. As far as I know, doctors do not track T2 and T1 and as you can read above, part of the reason for the post was to point out that our bodies make all four hormones but we thyroid patients who take synthetic hormone are only getting T3 and T4 (where as natural hormone replacement, such as Armour and NatureThroid, will have all four). When you say your blood work came back normal, were they checking Free T4 and Free T3, or just your TSH? It should have been all three, with an emphasis on FT4 and FT3. I’m sorry you’re going through this and am hoping things get better — and if your doctor is not listening, it might be time to find a new one if you’re losing hair and the doctor is not helping you deal with symptoms. Fingers crossed for you!!

      • Actually, the majority of Hyp-O patients are only receiving T4 supplements…as in Synthroid or Levothyroxine. The body converts T4 to T3……IF it is able to convert properly. But a doc can give the patient an RX for T3, most don’t though. Holistic docs are better for it.

  6. I read what you wrote about T1 and T2, and I want to let you know that what you said is WRONG!
    How dare you tell people that T1 and T2 don’t do anything to speak of.

    T1 and T2 when they are low in patients, causes sever depression.
    Hypothyroid patients that are on T4 therapy, and find themselves depressed, need to change to Armor thyroid, or equivalent, meaning thyroid medication that has T1,2,3,4, and Calcitonin.
    Once a patient that changes to this kind of treatment, their depression magically goes away after some time, it takes a couple of months, because the levels of the T1,2 are so low.

    • I don’t think that’s what the site is saying. They are saying that the medical industry does not regard T1 and T2 as important. That’s why our doctors only prescribe T4 and T3. From reading Katie’s comments, I believe the site is advocating natural hormone replacement drugs, like Armour, because they do find T1,T2, and Calcitonin to be important. If they are produced naturally, then they are important to our health and well-being and should not be ignored.

    • John:
      How dare you make such claims as T1 and T2 doing nothing…! Without providing links to credible scientific studies. For one thing there aren’t any studies proving it. Secondly, the body wouldn’t be making these hormones just because it has nothing better to do. So, to make the uneducated, undocumented claim that they have no function and jump on someone the way you did is incredulous. It wasn’t that long ago they didn’t even know T3 and 4 existed and how to measure and still they don’t really know all the details of how they work. Smart doctors are the first to admit it. An old saying…..”Absence of proof is not proof of absence”. Show the study buddy….that’s all I have to say in the end.

  7. Hello, Katie. I wanted to know how to go about finding a good open-minded, knowledgeable, progressive endocrinologist that would prescribe natural hormones to me. I have seen 5 doctors in the last 2 years and they’re all uncomfortable prescribing Armour or Naturethroid. I live in California (Los Angeles) so you think it would be easy, but it hasn’t been. Every doctor wants to give me synthetic Synthroid only. I’m finally on a combo t4/t3, but I really want to try Naturethroid. I have no thyroid and a horrible weight problem. My email: [email protected] if you want to respond this way. I am open to suggestions and will not jump on you for having opinions. I know you are not a doctor and I realize that I am responsible for my own health. I hope to hear from you soon.

  8. Katie Cleary says:

    Hi Natalie, thanks for the kind words and I am so sorry for all you are going through. I have a friend on NatureThroid who swears by it. I was never able to get a traditional endocrinologist to prescribe Armour for me, so I had to go to an integrative medicine practice. I believe naturopaths and functional MDs will also prescribe NatureThroid or Armour. Not living in LA area, I don’t know who to send you to, but there is this website that I found that lists holistic doctors:

    I can also post this question on the AutoimmuneMom facebook wall if you would like to see if others in the LA area could recommend someone. If you want to reply here or go to the facebook page and message me, I would be glad to post there for you. Take care and don’t give up until you get the right doctor – it is worth it to go on natural thyroid hormone replacement in my opinion – so glad you are pursuing this treatment path!

  9. Hi Katie,
    Thanks for your responses, I appreciate them, I find them very helpful and informative. My endocrinologist told me to repeat my blood test in 3 months and then she decides if selenium that she had prescribed would be enough or I should start thyroid hormone replacement. I will be following your new posts. Best regards

  10. hi my dr just told me that my t3 level is good but my t4 level is elevated so she wants to lower my syntyhroid . This upset me me & I am questioning her knowledge on throid because I am having serious issues of hypothyroidism yet she wants to lower my medication . It doesn’t make sense to me please help me out here

    • Katie Cleary says:

      Hi Pamela, I am not a doctor so please take this reply with that in mind. I also have Hashimoto’s hypothyroidism and agree that T3 is very important and so I would also question the dosage change. How you feel should also be taken into account – if you are still tired and having other hypo symptoms, I would not think a dosage change would be good for you. My best advice is to look for a second opinion, and I have has the best luck with integrative or functional medicine providers. You should be able to search for one on google, only problem is that some of them do not take insurance so make sure you know their insurance policy going in. Good luck and trust your instincts! Take care, Katie

  11. Dear All
    I have just been diagnosed with an underactive thyroid after being ill for 16 years and putting on over 4 stone in weight, despite telling Doctors over 12 years ago that I thought there was something wrong with my thyroid. I have been put on 5 mg a day of thyroxine. It has made me feel better and I have started to lose weight but I have also been very sick at times. I have very little understaning of the disease & my Doctor doesn’t seem to say much about it other than it is to do with the ‘brain function’, I note that the next blood test I have is to measure my ‘T2′ levels but there does not appear to be much info on these levels – most websites appear to mention T3 & T4. Also, my Doctor has not given a partcular name to the thyroid problem that I have – it appears to me that they are advised not to give out too much info!. Does anyone have any idea from the scant info I have given as to what my problem is in particular and is there anyone else out there with the same problem?. I had a throbbing in the back of my head everytime I laid down at night for years & it is such a relief that that feeling had now gone since taking the thyroxine,

    • Katie Cleary says:

      Hi Carol, thanks for your note – did you end up getting tested for T2? That is very uncommon and you are the first I have heard who is to be tested for that hormone. Usually doctors are testing Free T3 and Free T4, sometimes Reverse T3.

      I hope you are not still sick as that is not a typical reaction to going on thyroid medication from my understanding. Perhaps that was just odd timing. It does take a few weeks for your body to adjust to the thyroid hormone coming into your body, so don’t worry if you feel sort of “weird” for a bit – that is normal. Fingers crossed you have gotten some answers since you posted. Take care, Katie

      • Hi Katie

        Thank you for your reply . Yes, it appears that T2 must be unusual as it is rarely mentioned on these sites – I also believe that it the reason why it took so long to be diagnosed. My sickness has subsided a bit now and I am feeling much better.

        Kind Regards

  12. My Wife is hyperthyroid, she’s pregnant(First week of the 2nd Trimester) and taking Carbimazole (Like Methimazole) 15 mg/day (three doses), She’s measured the TH Levels, and the Total T4 was in normal range about 10 mcg/dl (normal 6-12), but the Total T3 was high 325ng/dl(normal 80-233), Should she increases the Carbimazole doze or not, and why the T4 level is within normal while the T3 is high????

    • Katie Cleary says:

      Hi Mohab,
      I did a quick google search and it could be that the T3 is high because she is pregnant – see this article: Hope that helps and hope she is feeling all right – know pregnancy throws off thyroid conditions and so it’s good you are keeping a close eye on things. All the best for both of you! Sending good thoughts.


  13. kanakapushanam says:

    what is the optimum level of t4..Why do different doctors use different measurements for the “normal” ranges of thyroid hormones?

    • Katie Cleary says:

      I too am unsure why there are so many different measures. Part of it has to do with the lab which is reporting the blood work and the ranges they use as in-range and out-of-range.

      Another complication is whether the doctor ordered Total T4 or Free T4.

      On my most recent blood work, the ‘normal’ range for Free T4 was .8-1.8 ng/dL.

      Stop the Thyroid Madness and Mary Shoman also have good info on thyroid lab tests.

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