Confused about the many thyroid hormones? Which is right for you?


A question that is frequently asked by women, “What is the best thyroid hormone?” and the answer is, “It depends!”

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No one magic thyroid hormone medication exists—instead a variety of factors must be considered. For instance, many people on thyroid hormones have a normal TSH but still suffer from hypothyroid symptoms. Others have a history of trying different thyroid hormones and getting different responses with each. Some do better with bio-identical (Armour), others with synthetic (Synthroid®). And for some, certain brands in either category make them considerably worse or better.



Do you even need thyroid hormone replacement?  When the autoimmune disease is successfully managed, thyroid hormones may not be necessary…However not taking them when you truly need them can have disastrous consequences for your health and well-being.

Choosing the right thyroid hormone

When choosing the appropriate thyroid hormone, three factors must be considered:

Sensitivity to fillers

Some people, especially those with autoimmune diseases such as Hashimoto’s, are sensitive to the dyes and fillers in thyroid hormone medications. Cornstarch, found in many brands, is a common trigger. Synthroid®, Westhroid, and Thyrolar contain cornstarch. A good example of how fillers can affect people occurred recently when Armour was reformulated with increased cellulose, decreased dextrose, and added cornstarch, which caused problems for many users.  Nature-Thyroid appears to be the most hypoallergenic brand.

Bio-identical versus synthetic hormones

I personally prefer my patients use a bio-identical thyroid hormone such as Armour. Lab tests can measure bio-identical hormones in your system, whereas they cannot measure synthetic hormones (only TSH is an effective marker when synthetic hormones are used). However, some people clearly do better with synthetic hormones, such as Synthroid®.

Why is that? This is common in people with an autoimmune thyroid disease, especially Graves’, who have developed an autoimmune attack against T3 and T4. In other words, their immune system is attacking their thyroid hormones. Because bio-identical hormones contain both T3 and T4, this stimulates the autoimmune attack and makes the person feel worse. In these cases, a synthetic T4 may be a better option. Currently there are no lab tests to test for antibodies against T3 and T4, however one is in development.

The function of T3 hormones

T3 is the active form of thyroid hormone, having the greatest impact on metabolism, but also carries the greatest risk of overdosing. People who have difficulty converting T4 to T3, or whose cells have become resistant to thyroid hormones, do better with thyroid hormones that include T3.

However some people develop hyperthyroid symptoms with T3 support — feeling wired, nervousness, insomnia, heart palpitations, etc. This scenario is most common in Hashimoto’s patients who have constant immune attacks against their thyroid gland, which releases excess thyroid hormone into the bloodstream. These people typically do better with a T4-only medication.

Assessing responses to thyroid hormones

Many thyroid hormone users have a history of trying various meds. Some thyroid hormones make people feel wired, jittery or nervous. Others bring TSH into a normal range but do not alleviate symptoms. Some worked really well. All of these reactions provide insight into the mechanisms involved in the hypothyroidism.

No significant response, but normal TSH

This is very common with those who have Hashimoto’s. Chronic inflammation, whether it is from unmanaged Hashimoto’s or other sources (injury, surgery, infection, cancer, overtraining), can cause three scenarios:

  • Prevents the conversion of T4 to T3
  • Hampers communication between the pituitary gland in the brain and the thyroid gland.
  • Inhibits thyroid receptors on cells from responding to thyroid hormones

In these cases, the response to T4-only medications will be poor. Another factor to consider is that the person may have many other conditions affecting thyroid health, such as insulin resistance, hormonal imbalances, gut infections, food intolerances, and more.

Only felt better with bio-identical hormones

This scenario can occur for several reasons:

  • Unable to convert T4 to T3 when using T4-only medication
  • Sensitivities to dyes or fillers in synthetic compounds that are not in bio-identical compounds
  • May need T3 due to problems with the thyroid hormone receptors on cells
  • Receptor sites on cells simply respond better to bio-identical than synthetic hormones

Only felt better with T3 combination hormones

If a person consistently does better with isolated T3 hormones, whether synthetic or bio-identical, a couple of factors are possible. One is difficulty converting T4 to T3. The other is that receptor sites on cells are resistant to thyroid hormones due to high cortisol, low progesterone, inflammation, high homocysteine, vitamin A deficiencies, and more.

Only felt better with synthetic hormones

This may occur in individuals who have an overactive metabolism and can’t tolerate additional T3. As mentioned earlier, this is common in those with Hashimoto’s who experience repeat immune attacks against the thyroid, or when the immune system is attacking T4 and T3, such as with Graves’ disease or multiple autoimmune diseases.

Felt over-stimulated with T3 or bio-identical hormones

Again, this may occur in the person with Hashimoto’s whose immune system is constantly attacking the thyroid gland, releasing excess thyroid hormone into the bloodstream. It also occurs in those with high epinephrine, an adrenal hormone, due to excess caffeine or nicotine, severe psychological stress, constant overtraining, or genetic mechanisms.

Felt fatigued and run down with thyroid hormones

This is almost always related to sensitivities to dyes or fillers in the thyroid hormone medication. It may also occur if the person is having an autoimmune response against their thyroid hormones, such as in Graves’ or in those with multiple autoimmune diseases.

Do you even need thyroid hormones?

Another factor to consider is whether you even need thyroid hormone replacement. Hashimoto’s, an autoimmune attack against the thyroid, accounts for 90 percent of hypothyroidism cases in the United States. When the autoimmune disease is successfully managed, thyroid hormones may not be needed at all, and taking them unnecessarily can do more harm than good. Another consideration is poor thyroid function caused by breakdowns in thyroid  pathways that need addressing, instead of true hypothyroidism (this is discussed in Chapter Four of the book).

However if damage to the gland is substantial enough, then thyroid hormones are necessary. Not taking thyroid hormone replacement when you truly need it can have disastrous consequences on your total health and well-being. If a person shows repeated and continuous elevations of TSH, thyroid hormones should be considered.

Even when thyroid hormone replacement is used, it is still vitally important to manage the autoimmune condition. This will enhance the effectiveness of the medication, preserve the integrity of the thyroid gland, and prevent the progression of the autoimmune condition into attacks on other areas of the body.

Thyroid replacement hormones

Brand Name Thyroid Hormones

  • Synthroid – synthetic T4 only
  • Levothroid – synthetic T4 only
  • Levoxyl – synthetic T4 only
  • Unithroid – synthetic T4 only
  • Cytomel – synthetic T3 only
  • Thyrolar – synthetic fixed ratio of T3 and T4
  • Armour – bio-identical fixed ratio of T3 and T4 combination
  • Westhroid – bio-identical fixed ratio of T3 and T4 combination
  • Nature-Throid – bio-identical fixed ratio of T3 and T4 combination

Generic Thyroid Hormones


  • Levothyroxine – synthetic T4 only
  • L-Thyroxine – synthetic T4 only
  • Liothyronine – synthetic T3 only
  • Liotrix – synthetic fixed ratio of T3 and T4 combination
  • Dessicated Thyroid – bio-identical T3 and T4 combination

Synthetic Thyroxine (T4) Hormones

  • Synthroid – Brand Name
  • Levothroid – Brand Name
  • Levoxyl – Brand Name
  • Unithroid – Brand Name
  • Levothyroxine – Generic
  • L-Thyroxine – Generic

Synthetic Triiodothyronine (T3) Hormone

  • Cytomel – Brand Name
  • Liothyronine – Generic

Synthetic T3 and T4 Combination

  • Thyrolar – Brand Name
  • Liotrix – Generic

Bio-Identical T3 and T4 Combination

  • Armour –Brand Name
  • Westhroid – Brand Name
  • Nature-Throid – Brand Name
  • Dessicated Thyroid – Generic


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