T3 References

For an introduction to T3, or triiodothyronine, see T3 Supplementation. Links to the T3 References pages are in the column at the right on this and every page in this section.

See also Desiccated Thyroid References and TSH References.

Highlights

• The most-referred-to study, published in the February 1999 issue of The New England Journal of Medicine, is listed on our Hypothyroidism, T3, Mental Function, and Depression page. Other studies in the Medical References section indicate similar results.
• T4-to-T3 Conversion and Hypothyroidism page: Read why in-range TSH and T4 levels may be present without adequate T3 levels.

A little background

The first treatment for hypothyroidism was with fried sheep thyroid, and with thyroid extract pills by the early 1900s. Although modern assay methods weren't available then, patients had long-term health improvement with this treatment. Thyroid extract, or desiccated thyroid, contains both T4 (thyroxine) and T3 (triiodothyronine) thyroid hormones.

In 1958, Synthroid became the first synthetic T4 medication, and others followed. Synthetic T4 was praised as being preferable to desiccated thyroid because it was easier at the time to assay its contents than the contents of desiccated thyroid, and because it was believed that thyroid patients need only T4, since T4 converts to T3 in people with normally-functioning thyroids.

Synthetic T3 came on the market later, and desiccated thyroid is still in use.

The need for these references

The buzz term for synthetic T4-only treatment for hypothyroidism is "the preferred treatment." It raises the unanswered question — preferred by whom? Certainly synthetic T4 is the preferred treatment for some patients with hypothyroidism, who do fine on it and sometimes do better than on the other options. Since patients have no difficulty getting treatment with synthetic T4 if they have a diagnosis of hypothyroidism, there is no need to compile medical references that support this treatment.

Synthetic T4 appears to be the preferred treatment of the majority of doctors. They can prescribe one pill instead of two, and most of what they've read tells them that it's enough for hypothyroid patients.

However, it is not the preferred treatment for the many thyroid patients who need supplemental T3 for real health improvement. Patients are increasingly researching their health conditions. Our "T3 Supplementation: Patients' Experiences" compilations (see the links at the right) show how hypothyroid patients got better when T3 was added to their medication.

Typically, patients who don't find synthetic T4 adequate first have to educate themselves about T3, and then find a doctor who will prescribe it. The doctor may already be knowledgeable about the use of T3, or may be willing to try it after reading about this treatment.

Medical articles and factors to consider

In virtually every study on the use of T3 combination therapy, some of the subjects found improvement with T4/T3 treatment versus T4 alone. (T4/T3 is not the preferred treatment for all hypothyroid patients, but unfortunately, it is often not even an option to try.) At the same time, other medical articles proclaim that T3 combination therapy is not necessary or preferred. Typical reasons given:

• Patients may have in-range lab results when on T4 only (but some other lab results point to the need for T3 — see T4-to-T3 Conversion and Hypothyroidism: References from Medical Journals).
• Long-term benefits of combination therapy have not yet been established (but desiccated thyroid is combination therapy, and it has been used successfully for over a hundred years).
• The short half-life of T3 can result in fluctuating T3 levels (but timed-release T3 is available, or patients can take pills two to three times a day, and the need for T3 is less at night anyway; also, some T3 may convert from the T4).

In some studies, the same doses are used for all the subjects, which doesn't take into account individual needs. A patient who may do well on 10 mcg of T3 in addition to T4, for example, will probably not do well on only 5 mcg, or on 20 mcg.

Only laboratory findings are considered in some studies, and patients' symptoms or lack of them while in the study aren't given weight. Since the purpose of the medical system is to help patients return to health and not just have in-range laboratory results, these studies are seriously flawed. Hypothyroid patients on T4 only whose lab numbers are in range (or often only the TSH level is checked) are repeatedly told that their symptoms can't be thyroid related. The patients who get well are those who find doctors willing to try thyroid medications containing T3.

The long-term shortcomings of T4-only therapy have been documented. Large numbers of patients still have symptoms of hypothyroidism after years on synthetic T4 only, even with low TSH levels. When T3 is added to their treatment, these symptoms usually disappear.

Increasingly, doctors are paying more attention to T3, as can be seen by the number of recent medical articles on the topic. As Dr. Anthony Toft (UK) wrote in 2002 about T3 therapy: "It would appear that the treatment of hypothyroidism is about to come full circle."

Lois Summers
with Kevin G. Rhoads, PhD