This article is part of a special report on Thyroid Disorders. To see the other articles in this series, click here ^[1].

In this final article in the series on Low T3 Syndrome ^[2], we’ll discuss whether thyroid hormone replacement therapy is an appropriate treatment in these cases.

Unfortunately, there are few studies that have examined this question specifically, and even fewer that have explored the question of whether T4 or T3 (and which type of each) would be the best choice.

As a clinician, my primary concern is always primum non nocere, or “first, do no harm.” From this perspective it’s important to recognize that the changes seen in Low T3 Syndrome may represent a restorative physiological adaptation by the body to chronic illness. In other words, T3 levels are low because the body is attempting to conserve energy and resources to better cope with the challenges it is facing. Increasing thyroid hormone levels in this situation could conceivably have adverse effects.

For example, the changes observed in the thyroid axis in acute illness are similar to those observed in fasting, which can be interpreted as an attempt to reduce energy expenditure and protein wasting. (1 ^[3]) Giving fasting subjects thyroid hormone results in increased catabolism (breakdown). (2 ^[4])

In cases of chronic illness, however, it is less clear what effect thyroid hormone replacement has. The few studies that have been done produced mixed results. (3 ^[5])

Some studies show that treatment causes harm, others show no change, and still others show an improvement. After reviewing the literature on this, I’ve come to the following tentative conclusions:

• T4 is rarely, if ever, effective in Low T3 Syndrome and may even cause harm. This is probably due to the decreased conversion of T4 to T3 that is seen in chronic illness.
• T3 replacement has been shown to be consistently beneficial only in cardiac patients who’ve recently had surgery, heart failure or a transplant.

That said, I’ve heard anecdotal reports of improvement from people who have taken replacement T3 hormone for a condition called “Wilson’s Syndrome” (which does not exist ^[6] in the scientific literature or according to any mainstream medical organizations). Wilson’s Syndrome refers to low basal body temperature and other nonspecific symptoms occurring in the presence of normal thyroid hormones.

I’ll be the first to admit that “lack of evidence is not evidence against”, and as I mentioned earlier, there’s not a lot of research on the effectiveness of T4 and T3 replacement therapy in Low T3 Syndrome. It may be that as we look into this further, we’ll discover a role for thyroid hormone replacement in these conditions.

That said, I think caution is warranted. Taking T3 when you don’t need it is potentially dangerous. It can significantly upregulate the metabolic rate and lead to cardiovascular complications in some patients. And, if the changes seen in Low T3 Syndrome are a compensatory adaptation of the body in response to chronic illness, increasing T3 levels artificially may have undesirable effects.

In the majority of cases of Low T3 Syndrome, I think it’s preferable to identify the underlying cause and treat that. As I discussed in articles #3 ^[7] and #4 ^[8] in this series, those causes most often include infections, autoimmunity and inflammation.

Have any of you tried thyroid replacement for Low T3 Syndrome? If so, what was your experience? Please let us know in the comments section.

Articles in this series:

• Low T3 Syndrome I: It’s Not About The Thyroid! ^[2]
• Low T3 Syndrome II: Myths and Misconceptions ^[9]
• Low T3 syndrome III: Inflammation Strikes Again ^[7]
• Low T3 Syndrome IV: An Autoimmune Disease You’ve Never Heard Of? ^[8]
• Low T3 syndrome V: Should It Be Treated With Thyroid Hormone? ^[10]