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3 Steps to Choosing the Right Thyroid Hormone


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This article is part of a special report on Thyroid Disorders. To see the other articles in this series, click here.

I often get comments and emails from people asking me which thyroid hormone I think is best. My answer is always the same: “It depends.” As much as some practitioners would like to make us believe, there is simply no “one size fits all” approach to thyroid hormone replacement.

Statements like “Synthroid is best” or “I prefer to use synthetic T4 with my patients” or “I only use bio-identical hormones” demonstrate a lack of understanding of thyroid pathology. Why? Because, as I’ve explained in this series, the underlying causes of thyroid dysfunction are diverse.

Giving all patients the same thyroid medication without understanding the mechanisms involved is analogous to not checking a patient’s blood type before doing a transfusion. Granted, the consequences may not be as severe, but the underlying principle is the same.

Before we continue, let me remind you that I’m not a doctor and I’m not offering you medical advice. My intent is to educate you about the various considerations that should be made when choosing a thyroid medication, so you can discuss them with your doctor. Understood? Great. Let’s move on.

Choosing the right thyroid medication requires answering the following three questions:

  1. What’s the mechanism that led to the need for medication in the first place?
  2. Are there any mechanisms that may interfere with the actions of the medication?
  3. Does the patient have sensitivities to the fillers used in the medications?

Let’s look at each of these in turn.

What’s the Mechanism That Led to the Need for Medication in the First Place?

If you’ve been following this series, you know that there’s no single cause for low thyroid function. Do you have an autoimmune disease (Hashimoto’s) causing destruction of your thyroid gland? Do you have high levels of estrogen causing an increase in thyroid binding proteins and a decrease in free thyroid hormone? Do you have a systemic inflammatory condition affecting your ability to convert T4 to T3, or decreasing the sensitivity of the cells in your body to thyroid hormone?

In order to choose the right hormone, you have to know what the underlying mechanism causing the dysfunction is. Let’s look at an example.

Say you have a problem converting T4 to T3. In this situation, your TSH may or may not be slightly elevated, but let’s say it is, and your doctor prescribes Synthroid. Synthroid is a synthetic T4 hormone. Will this help you?

No. It won’t help because your problem in this example isn’t a lack of T4, it’s an inability to convert T4 to the active T3 form. You could take T4 all day long, and it won’t do a thing unless your body can convert it.

The first step in this case would be to address the causes of the conversion problem (i.e. inflammation), in the hopes that you may not need replacement hormone. If that doesn’t work, though, what you’d need in this situation is either a so-called bio-identical hormone that has a combination of T4 and T3, or a synthetic T3 hormone (like Cytomel). These will deliver the T3 you need directly, bypassing the conversion problem.

Are There Any Mechanisms That May Interfere with the Actions of the Medication?

The vast majority of long-term hypothyroid patients that haven’t been properly managed find that they constantly need to increase the dose of their medication, or switch to new medications, to get the same effect.

There are several reasons for this. First, inflammation (which is characteristic of all autoimmune diseases, and Hashimoto’s is no exception) causes a decrease in thyroid receptor site sensitivity. This means that even though you may be taking a substantial dose of replacement hormone, your cells aren’t able to utilize it properly.

Second, elevations in either testosterone or estrogen (extremely common in hypothyroid patients) affect the levels of circulating free thyroid hormone. For example, high levels of estrogen will increase levels of thyroid binding protein. Thyroid hormone is inactive as long as it’s bound to this protein. If you take thyroid replacement, but you have too much binding protein, there won’t be enough of the active form to produce the desired effect.

Third, there are several medications that alter the absorption or activity of T4. These include commonly prescribed drugs like antibiotics & antifungals (i.e. sulfonamides, rifampin, keoconazole), anti-diabetics (Orinase, Diabinese), diuretics (Lasix), stimulants (amphetamines), cholesterol lowering medications (Colestid, Atromid, LoCholest, Questran, etc.), anti-arrhythmia medications (Cordarone, Inderal, Propanolol, Regitine, etc.), hormone replacement (Premarin, anabolic steroids, growth hormone, etc.), pain medication (morphine, Kadian, MS Contin, etc.), antacids (aluminum hydroxides like Mylanta, etc.) and psychoactive medications (Lithium, Thorazine, etc.).

All of these factors must be considered if a particular medication isn’t having the desired effect.

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Does the Patient Have Sensitivities to the Fillers Used in the Medications?

Another important consideration in choosing the right hormone is the fillers contained in each medication. Many popular thyroid medications contain common allergens such as cornstarch, lactose and even gluten. As I explained in a previous post, most hypothyroid patients have sensitivities to gluten, and many of them also react to corn and dairy (which contains lactose).

Synthroid, which is one of the most popular medications prescribed for hypothyroidism, has both cornstarch and lactose as a filler. Cytomel, which is a popular synthetic T3 hormone, has modified food starch – which contains gluten – as a filler.

Even the natural porcine products like Armour suffer from issues with fillers. In 2008, the manufacturers of Armour reformulated the product, reducing the amount of dextrose & increasing the amount of methylcellulose in the filler. This may explain the explosion of reports by patients on internet forums and in doctor’s offices that the new form of Armour was either “miraculous” or “horrible”. Those that had sensitivities to dextrose were reacting less to the new form, and experiencing better results, while those that had sensitivities to methylcellulose were reacting more, and experiencing worse results.

The best choice in these situations is to ask your doctor to have a compounding pharmacy fill the prescription using fillers you aren’t sensitive to. Unfortunately, insurance companies sometimes refuse to cover this.

Other Considerations

Another common question that is hotly debated is whether bio-identical or synthetic hormones are best. Once again, the answer is: “It depends.” In general I think bio-identical hormones are the best choice. A frequently perpetuated myth (in Synthroid marketing, for example) is that the dosages and ratio of T4:T3 in Armour aren’t consistent. Studies have shown this to be false. Armour contains a consistent dose of 38 mcg T4 and 9 mcg T3 in a ratio of 4.22:1.

However, in some cases patients do feel better with synthetic hormones. One reason for this is that a small subset of people with Hashimoto’s produce antibodies not only to their thyroid tissue (TPO and TG), but also to their own thyroid hormones (T4 and T3). These patients do worse with bio-identical sources because they increased the source of the autoimmune attack.

Another issue is the use of T3 hormones. As we’ve discussed, T3 is the active form and has the greatest metabolic effects. The flip side of this, however, is that it’s far easier to “overdose” on T3 than on T4. Patients with trouble converting T4 to T3 do well on synthetic T3 or bio-identical combination T4:T3 products. But for many patients with Hashimoto’s, which is can present with alternating hypo- and hyperthyroid symptoms, T3 can push them over the edge. They are generally better off with T4 based drugs.

As you can see, the best thyroid hormone for each patient can only be determined by a full thyroid work-up and exam, followed by trial and error of different types of replacement medications. Such a work-up would include not just an isolated TSH test, but also a more complete thyroid panel (including antibodies), other important blood markers (glucose, lipids, CBC with diff, urinary DPD, etc.) and possibly a hormone panel.

A history must be taken with particular attention paid to the patient’s subjective response to replacement hormones they may have tried in the past.

Unfortunately, this rarely happens in the conventional model, where the standard of care is to test only for TSH. If it’s elevated, the patient will get whatever hormone that particular practitioner is fond of using without any further investigation. And all too often, as many of you can attest, this simplified and incomplete approach is doomed to failure.

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Join the conversation

  1. Hi. I really like your articles – very informative. I’m combing through the one about the gut and hypothyroid. I was diagnosed with hypothyroid after the birth of my second child in October 2011. I’ve been told by two doctors (a GP and a homeopathic doc) that I have Hashimoto’s. I’ve never been sure of this. How can I find out the ‘source’ of my hypothyroid? Should I see an endocrinologist? My docs just give me medicine and send me on my way with a ‘well, it won’t kill you’ attitude and don’t want to go any further.

  2. Love this article. It is so great that I included it in my post at Hypothyroid Mom this week “Which Is The Best Thyroid Drug For Hypothyroidism”. I was so curious about what you wrote about Cytomel having modified food starch that contains gluten. I am very curious about this because I’ve tried different brands and feel my best on natural desiccated thyroid. When I tried a combination of Levothyroxine and Cytomel, I just didn’t feel as good as on natural desiccated thyroid. I know we are all individual in how we respond to these drugs but I had no idea that Cytomel had a modified food starch that contains gluten. This would explain why some hypothyroidism sufferers report not feeling great on Cytomel.

  3. Chris – I was just diagnosed with Hashimoto’s on Saturday. I love your site – but I honestly don’t know where to go from here. I know you have info on gut dysbiosis etc. – but everything is so detailed I don’t even know how to start! I can’t imagine trying to figure out the Omega 3 vs. 6 issue today…but I know I need to get this all right. What is my next step?

    • S, I would suggest contacting NUTRI-SPEC.NET to find s Dr. near you….searching their site about thyroid would also make you more informed than most endo docs

  4. I have been in and out of the hospital for three years now after first having a botched pituitary tumor removal that resulted in coma and damage to the pituitary, then follow up brain radiation to shrink it (damaging the pituitary further) and one month after that I was diagnosed with an aggressive thyroid cancer and had a complete thyroidectomy. Since then, I have had cortisol readings all over the place, prolactin levels at 150+, stroke events that cause complete left side paralysis which eventually just go away, massive migraines that supposedly cause these migraines, and constantly fluctuating thyroid levels regardless of the brand or dose of medication. My cortisol level is very low as well, and my endocrinologist wants me to take hydrocortisone as well now. I feel like crap, can barely function, and now I am suffering from extreme panic attacks which I have never had before – they are very frightening and feel like full blown heart attacks. Nobody can quite figure out what is wrong with me despite test after test and doctor after doctor. I also have gluten intolerance and arthritis, nobody has ever told me if I have Hashimotos or if that can even be possible once the entire thyroid is removed, I am at my wits end and I don’t know what to do anymore. I am about to be tested for ACTH cortisol corsytropin stimulation next week, my doctor suspects adrenal insufficiency. Regardless of that, why is it so difficult to get my thyroid levels regulated since I don’t have a thyroid to compete or throw off the medication? I am confused, faced with only ONE endocrinologist within 50 miles, and he and his partners are rude (literally yell at me sometimes when the meds don’t work the way they say they will) and they do not seem interested in getting to the bottom of things…they just spend 10 minutes or less and don’t listen. I have no health insurance and cannot work from the issues my health causes, and I can’t afford to keep seeing doctors without getting some solutions. I hate taking so many meds, and I prefer more natural solutions when possible. Anybody have any ideas? I would literally travel hundreds of miles if I thought I could see a doctor who would look at all the information and really treat ME, not just a few numbers on a lab report.

    • Is it true that hypothyroidism can cause low progesterone? If low progesterone is fixed, does that mean you don’t have a thyroid issue aNy longer??

      • Kristin,
        Ray Peat has a lot of information about progesterone issues/thyroidism. Google Ray Peat – progesterone to see his articles on his website.

  5. I have been on Levoxol 50-75 mcg since 2001. What a nightmare. I feel exhausted
    ALL the time. My once thick long nails are
    tissue thin as is my hair. there are no specialists where I live that address just thyroid tx. When 1st put on meds I was only
    borderline hypo…any suggestions?

  6. Chris,
    This is a very helpful article. I wondered if you could answer the question about Cytomel being or not being gluten-free. I have a letter from the manufacturer (to me) stating that it is gluten-free. If there is any evidence that it is not, I should not be taking it as I have Celiac Disease.

  7. T3-only is also best for those with reverse T3 issues because as long as there’s T4 available, the body will continue to convert T4 -> rT3 and the person will never get better. Doesn’t matter if it’s natural, unnatural, or your own T4, when your body gets into the “mode” of making rT3, it ekeps doing it.

    I do not have Hashi’s and as far as I know have a perfectly normal thyroid gland. However, due to diabetes and adrenal insufficiency, I wound up literally bedridden with severely elevated rT3. Hydrocortisone fixed up the AI, and very large doses of T3 (enough to suppress both TSH and FT4 entirely) cleared the rT3.

    I now maintain on a very low dose of T3, just enough to keep the rT3 at bay and have “normal” bloodwork.

  8. Debbie,

    Yes, if you can achieve the results you want with licorice or other natural adrenal tonics that would be best. As I’m sure you’re aware, corticosteroids have adverse effects on the immune system, bone health, weight regulation and cardiovascular function – among other things. Taking them over the long-term should be avoided if possible.

  9. Chris,
    I’m hoping you answer my question from 9/23, but in the meantime I’ve dropped down to 25 mg. Cortef and 1 or 2 Isocort pellets before bedtime.

  10. They can be, but to get the most benefit the underlying mechanisms have to be addressed.

    • Hello Chris, I have been taking Armour Thyroid all of my life since I was 3 and I am going on 57 and when I take the other like Levothyroid and Synthroid it is like I am not taking nothing at all and my got up and left me I will not take anything else I was on 90 mg . 1 1/2 grain and now they are decreasing they found a cyst on each side of my Thyroid Gland and they said the 90 was suppressing the TSH and I want to know more about the RT3 I was adviced to go with sites that ended in endu and gov that I needed to be careful with the other information given out !!!!!!!!!!!!!

      • I have been on Armour for 5 years and have been feeling much better.
        Recently my 21 year old daughter was diagnosed with hyperthyroidism and the doctor said that Armour was going to be discontinued and that it is not good for you. I was looking for information on this, I have not found any? Also, I was interested in what other meds address both T3 and T4?

        • Wow. So wrong. The company making Armour changed again not too long ago; they may change the fillers, but they will continue to produce it.

          There are lots of NDTs (Natural Desiccated Thyroid meds), most of them have a generic, and some are available over the internet and in health food stores. Prescription NDTs are all FDA-approved and legally available, just like synthetic T4 (Synthroid is the brand, Levothyroxine is the generic) and T3 (Cytomel is the brand, Liothyronine is the generic). Each med has different fillers.

          21st century medical science has proven that the T3 converted from T4 is not enough. Prescription NDTs are made from pigs’ thyroids, and they also have T2, T1, and calcitonin, just like human thyroids.

  11. Chris,
    Your comment:  I don’t recommend people take hydrocortisone in general. It’s preferable to take natural compound like licorice extract to boost endogenous cortisol production than to take cortisol directly.
    I had several tests that determined I have secondary adrenal insufficiency and am currently on 35mg Cortef since my body doesn’t produce enough. Are you saying that licorice would still be preferred to supplemental hydrocortisone?
    Really great post (and blog).  Thanks!

  12. Thanks so much, this sheds a lot of light on some things for me. I tried bioidentical thyroid medication for over a year, and it did nothing to help my thyroid symptoms. So I went back onto synthetics (both T3 and T4) and saw an immediate improvement. My doctor prefers the bioidentical, but said to use what works. He wasn’t really sure why synthetics worked better for me. This is the first time I have read anything that gives a clue to why!

  13. Spectacular stuff. It’s amazing what kind of disorders improve with good nutrition, good eicosanoid balance, gut flora, and eliminating stuff like wheat. I’ll share this series like I do all your other ones.

  14. Chris,
    Something to think about before taking the conventional way (synthetic T4):
    Hypothyroid persons using conventional treatment (synthetic T4) usually have higher levels of free T4 and lower levels of free T3 than normal persons (see Pubmed 20693806 for a comparation in pregnant women).
    Hypothyroids taking thyroid medications progressed more rapidly to a diagnose of Alzheimer’s than hypo not taking thyroid medications (Pubmed 19666883).
    Higher total and free T4 levels are associated with increased risk of dementia and Alzheimer’s (Pubmed 17870208, 17136019, 17132968, 16636121).

    • Very interesting comment, and would like to see more conversations on this concern! Thank you for sharing.

  15. Wow Chris,

    a truly penetrating look into an issue that proves so frustrating for so many patients AND M.D.s   Thyroid disease is rampant,  thyroid misdiagnosis is rampant, and thyroid mis managment is rampant. 

    As illustrated in your article there is a reason for all this……it is a very complex issue that needs careful testing, managment and observation. 

    I am going to bookmark this and send it to many patients.

    Thank You

  16. Read the comments to one of your previous posts where you mentioned panax ginseng treatment for adrenal fatigue. That sounded interesting, but I have already been recommended to take hydrocortisone tablets for those problems. How do these two substances work toghether, is it possible to combine them?

    • I don’t recommend people take hydrocortisone in general. It’s preferable to take natural compound like licorice extract to boost endogenous cortisol production than to take cortisol directly.

      • Licorice has more of a mineralcorticoid effect than a corticosteroid effect, so should not be taken by those with high bp.

        Also, whether it’s effective is going to depend non how low cortisol someone is. For example, if you have high cortisol in the morning, and low at noon, licorice in the morning is very effective as it extends the life of cortisol in your body.

        However, if your body flatout can’t make enough cortisol, you need hydrocortisone (or another steroid, though I think HC is best as it can be dosed in a diurnal pattern).

        Really, you can’t determine the best treatment for someone without a 4x diurnal saliva test to see the specific pattern of dysfunction.

        For example, many folks who are low all day wind up high at night with insomnia. This is because the pit keeps putting out ACTH in response to the low all day and the adrenals can’t keep up, but they can produce enough to go over range at night. So… a person with this pattern may need doses of HC at 7AM, 11AM and 3PM but then need PS at night to lover cortisol to allow sleep. (Though usually when on enough HC during the day, the sleep problems will dissipate).

        Lots of info here: http://adrenalsweb.org

      • Hello
        I have been taking 25 of synthroid for the past couple months my hair has fallen out really bad. I have seen so many doctors and they say that the synthroid would not cause my hair to fall out, but it’s a side effect on the label. Have you ever heard of synthroid causing hair to fall out? My hormone levels are:
        TSH 3.51
        T3 free 2.9
        T3 UPTAKE 29
        T4 6.4
        Thank you 🙂
        T3 TOTAL 91

        • Rigorously screened, healthy volunteers tested between .4-2.5 for TSH results. Your result is too high (meaning, you deserve some help). 25 mcg T4-only is not much help. Unfortunately for you and millions of others, it IS the “acceptable” standard of “care”. I suggest you learn how a healthy thyroid works, then self-treat, if you can’t find a doctor who runs appropriate tests. Appropriate tests are TSH (if you still have a thyroid with which your PITUITARY can communicate), Free T4, Free T3, Reverse T3, and antibodies (plural). There are four antibodies. Antibodies are evidence of autoimmune disease, not thyroid disease. Ingesting thyroid hormones isn’t treatment for antibodies. 🙁

          • How can we self-treat? Don’t I have to get the prescription from the doctor? Mine tests only for tsh and keeps saying I’m too high even though his low dose sent me into a deep depression that was “miraculously” cured when I upped my own dose. After ten days the depression lifted. But when I went to get a refill, he tested me again, again said I was too high even though I had low-thyroid symptoms all over the place, and I’m having trouble finding a doctor in my area who will prescribe according to how I feel. If I just take extra, this doctor will know I’ve run out too early.

            • Google Thyroid-S, ThyroGold. These are over the counter NDTs like Armour. They contain T4, T3, T2, T1, calcitonin and fillers. Joining one of the “FTPO (For Thyroid Patients Only) groups on Facebook will connect you with someone who can help you self treat.

              You noticed a difference after ten days because your T4-only med takes 7-10 days to get to your liver, get converted and back out to your cells. The T4 you ingest today isn’t used by your body until sometime next week. The T3 in an NDT works the same as the T3-only meds: it gets to work within 30-45 minutes of dissolving it in your mouth, and wears off 3-6 hours later. Women need more T3 than men; our TSH and Free T3 fluctuates during the day; and our T3 needs to fluctuate during our cycle with our other hormones’ fluctuations. If you don’t know your body and you don’t understand how a healthy thyroid works, I don’t suggest self-treating.

              To try to find a doctor who “deviates” from the “acceptable” standard of “care”, you call ahead and ask, does he/she prescribe T3 and/or an NDT. Sometimes, ob/gyns are more willing; sometimes your primary care doc will help if you copy articles for them, present your case with your documentation of symptoms. If neither of those options exist, try a DC’s office or a naturopath, or an integrative physician.

              Thyroidchange.org has a list of doctors who support their efforts….

              • Thankyou, that helps a lot. I didn’t realize the difference of dispersal between the T3 and T4. I know my body pretty well but have had trouble understanding how the replacement hormones work. So many books written about it, I read them and it seems so complicated, but maybe I’m just seeing it that way.
                Thank you for taking the time to explain a bit to me. Will look for a new doctor for sure.

                • Karen,
                  I’ve found a great doctor that takes full panels and treats based on symptoms. I found her by going to worldhealth.net and searching in my state. Then I picked the one with the most accreditations in integrative medicine. I live in MS.

                • Thankyou, Leigh, I will check that site. I don’t guess the doctor you found is in south MS? I’m in the FL panhandle.

            • Karen,
              Forward Health Solutions in Hattiesburg, MS. I’m still in the early stages, but they are already trying adjustments. Best wishes.

        • Hello. My hair fell out before i was medicated and once i was put on synthroid it got even worse. It is from the synthroid!!!! Not sure if it is the meds itself or just not being at an optimal level and that is why it happens. I have been on Levo, then synthroid brand name, then combo of Synthroid and generic cytomel, then armour and then back to synthroid only and now armour again…..all different doses too. NDT i have found is best for most people because it is the closest to what our own body secretes, however there are a small % that do better on T4/T3 combo of synthetics. My hair stopped falling out once i got on NDT.