3 steps to choosing the right thyroid hormone


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.

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.