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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. I have had Hashimoto’s for over 30 years, first diagnosed post partum after my first child. My antibodies have stayed in about the same high range despite the paleo autoimmune protocol. My TSH has been brought to the functionally optimum range of about 1, but I have always had borderline or low normal free T4 and low normal free T3. I struggle with weight despite a carb load usually 50 – 100 grams. I wonder if I may be making antibodies to the T3 and T4, as described by Chris in the article and that is the reason I can’t get my hormones up to an optimal level. Would that be a reason? Are there any tests to determine if this is the case or does one just need to try the synthetic hormones and see how it goes? Any information would be helpful.

  2. One of the greatest moments in this world is when you see your own wife put to bed, this awesome moments makes you a man and not just a man a real man. My wife suffered from Fibroid which made her unable to get pregnant and give us a child for almost 18 years with multiple surgeries done and none seemed to help the situation. I almost gave up but due to the love i had for her because i married her a virgin i had to find a way to help her. I told a member of my church who recommended Dr. martin to me, i contacted him and he sent me a medicine and this medicine shrieked it naturally in weeks it was like magic but it’s science. I am happy writing this because she delivered yesterday a baby girl. Do not loose hope too soon contact him. i am confident he will help you too.

  3. Hi Chris
    Thank you for your info
    I was doing fine on Erfa but with high levels of free T4 and t3, (no hyper symptoms) until my Endo took me off and halved my equivalent dose, putting me on levothyroxine. It’s been horrendous. I now have a diagnosis of fibromyalgia. I recognise I had this before the natural thyroid, so I know the natural stuff would sort me out again.
    SInce all the problems with NDT fillers, I don’t know which one to try. Do you know whether Erfa is now back to normal, DEC 2016, because I used to be ok on that, but I hear it had a formulation blip.
    Does cellulose filler bind to the hormone?
    I am gluten free, plus other insensitivities (many).
    My chiropractor says that non celiac gluten intolerance can be much more difficult than celiac, and that we should avoid even corn and refined rice, all the cereals, except wild black rice. It’s so hard!
    Summary, I want to know which NDT is closest to the old formulations that were soft, i.e. Not so much cellulose. However preferably not using dextrose made from wheat! Thank you

    • Very interesting comment and questions which I hope someone can answer! I’d be interested to find out myself…I have been taking Thai NDT for the past year, after having problems with Erfa back in late 2015, and my latests labs showed midrange FT4 levels and FT3 levels out of range 24 h after taking meds. Yet, no hyper symptoms, I feel good and have much more energy. But I am not sure what ideal FT3 and FT4 levels are supposed to look like when optimally dosed on NDT; if you go to the lab 24 h after taking latest dose, I imagine they would need to be lower than if you take meds the same day you have labs done…? I read somewhere that you can count on your FT3 levels to be +/-20% higher on the previous day if you have not taken your meds before having labs done, and that FT4 levels are basically meaningless once on drugs containing T3, as only FT3 levels count…can anyone corroborate that or does T4 have a role on its own?

    • You said your Dr took you off because you had high T4 and T3. Did you take your thyroid med before your labs? If so then it will cause falsely elevated levels, especially the T3 level. Because T3 is the active hormone it loads to your system right away, do taking your med before the lab draw will show a false high level. Most Drs who understand this have their patients fast from T3 containing meds for at least 12 hrs before labs for accurate results and advise to bring it with and take it after. Dr. Isabella Wentz, Thyroid Pharmacist also has an article about this.

  4. I have been following this blog for a while now and today i felt like i should share my story because i was a victim too. I had endometriosis for 18 years and i never thought i would ever get a cure due to the terrible symptoms i had and this made it impossible for me to get pregnant even after 12 years of marriage and it was a serious issue. I got to know about Dr. Aleta who treated someone and the person shared a story of how she got a cure and let her contact details, i contacted Dr. Aleta and she actually confirmed it and i decided to give a try too and use her herbal medicine that was how my burden ended completely. My son will be 2 this december and i am greatful to God and thankful to her for medicine too. If you have (Endometriosis, PCOS, Fibroid, Ovarian cyst, Ectopic Pregnancy or any infertility issues) just reach her on (aletedwin @ gmail. com) she has professional advise and a cure too.

  5. Thank you for sharing.

    Curious you say:
    “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.”

    Is there research to support this?

    My tpo keep going up or staying same on bio-identical and I am gluten free, no old fillings, good nutrient levels, have done many of the things I should do… wondering if I am one of these people and I how to figure that out.

    • I just wanted to add that I fall into this category- I was on synthetic t4/t3 and had much better/stable numbers- when I switched to NDT, no matter how much we tried to increase the dose, my numbers just tanked! I have a large clustering of autoimmune diseases- have to get most medications compounded due to filler issues and my immune system just destroyed the NDT! It is rare, but does happen! I am now taking Tirosint with compounded t3 with better success!

  6. Hi all, 31yo M, 5’9 135lb. I was just diagnosed with hypothyroid by my ND. Low T3 (.6!), high LDL, low alkaline phosphatase, low HCT, low RBC/WBC. What my ND told me is basically border-line anemic (but my iron levels are great) and need to take Cytomel. This is after a 10year battle trying to figure out my IBS, with IBS-A and constipation. The thing is I’ve been losing weight, have enormous stools (lots of undigested food), but otherwise feel fine. Stool tests also reveal complete lack of ANY good bacteria (no SIBO). So I’m wondering if Cytomel to fix thyroid is enough, or if I need to supplement with selenium, iodine, etc. Unlike typical hypothyroidism, I don’t have weight gain (in fact WEIGHT LOSS) but have mild coldness and mild brain fog/tired. This all started with trying to regulate digestion so I wasn’t spending 1.5hr in bathroom daily, and now it’s progressed to thyroid! Thoughts?

    • Hola soy de guanajuato habrá alguna otra manera de poderme comunicar con ustedes

    • Yes get a LYME & Babesia panel done at IGENIX or MDlabs.com . Insurance won’t pay so don’t ask. Lyme attacks white cells, Babesia attacks red cells. They usually are in same insect & act synergistically to make you ill. Fibro, cfs, allergies, gastro problems, thyroid etc.

  7. Hi Chris,

    I had a thyroidectomy in April 2015 due to cancer. I was first on Levothyroxine 100 but my menstrual cycles were very heavy and nonstop. I then developed anemia. My tsh was over 50. The doc then put me on Synthroid 125 which was ok, but my tsh was 22. The dr increased the Synthroid to 137mcg but it gave me joint pain and fatigue. I had to quit tennis and hiking. My knee blew out and feet swelled, but tsh was 9. My joints are a mess. I tried switching to NatureThroid 150, but the dose was too hard on my heart and felt like I was having heart attack. Now I am back to Synthroid. Any advise? I feel like these doctors don’t care (I have been to 3 endos). I wish someone would have told me what the aftermath was like because I wouldn’t have had the surgery. Another 10 years of a good life is far better than 20-30 of being miserable.

    The best I felt was on Synthroid 125 but the docs wont let me go back down on dosage. Doesn’t quality of life count for something?

    I keep wondering if there is a good way to convert to Naturethroid that doesn’t hurt your heart such as starting on a low dose and moving upward slowly? I think 150 was way too high. Any thoughts?

      • Tirosint caused me severe problems – I developed Parkinsons type symptoms and severe brain fog within three weeks of Tirosint usage. It made me severely dizzy, off balance, shaky with severe tremors.

        EEI would stay far away from it for me. Each of our bodies are sooooo different and it does not mean that it will work for all of us. Best to allow your body to tell you what it is that works for it.

    • Im sitting here in awwwwe, Ive had my thyroids removed 12/13 and each year feels worse than the first. My hair is so brittle, breaking. My knees started popping and cracking about 7 months or so ago. Im sluggish & depressed. I weigh the most I’ve Ever. The only thing my endocronoligist is doing is “regulating” my medicine. Well after reading and researching im going to see Hormone Dr.

      • Kate,

        You should try Levothyroxine, the generic hormone replacement. It is not comparable in dosage to Synthroid and it may work for you.

        Good luck!


        Have you thought about changing your diet and going gluten free? Here are some books that provide lots of information about diet and autoimmune diseases. THE GLUTEN FREE EDGE; IT STARTS WITH FOOD; THE WHOLE 30; just a few. It will help with controlling your cholesterol also.

        • Tirosint is the only thyroid hormone I could take. It is not generic. I too had a thyroidectomy due to a huge goiter. They tried me on Levothyroxide and it was a disaster. So my endo suggested I use Tirosint. It has been a blessing!!! I feel like a normal person now. Ask your doctor about it… Also google it! 🙂 Hope this helps!

    • You were started on too high a dose of ndt. It contains T3 and this can be a shock to the system. You have to work up slowly. Look at the Stop the Thyroid Madness website for advice.

    • You always start low on synthetic or armour thyroid. Read the Book by 14 M.D.s called “Stop the Thyroid Madness” – they are proponents of Armour thyroid. You can check out the website as well.

  8. My thyroid doctor just retired and I am looking for a good thyroid in Phoenix Arizona area.
    Thank you!