Why T4-only Medications Often Make Hypothyroidism Worse, and the Problem With TSH Tests

Hashimoto’s Article Series

Hypothyroidism used to be diagnosed by evaluating symptoms and using basic diagnostic tests, all of which centered around the metabolism – it was understood that hypothyroidism and a lack of energy went hand-in-hand.

Doctors would note symptoms, such as fatigue, and measure the patient’s metabolic rate, temperature, pulse rate, and reflexes. If these measures suggested hypothyroidism, patients were given small doses of animal thyroid hormones until their symptoms and measures improved, which they often did. At the time, it was also known that hypothyroidism was extremely common, including as much as 40% of the population.

Since then, it has been discovered that your thyroid gland produces several hormones, the primary ones being T3 and T4.

  • T3 is active and short-lived – it tells your cells to increase their metabolism, or energy production, and is then quickly broken down.
  • T4 is inactive and long-lived – it doesn’t have much of an effect on its own. Instead, it waits around until it’s converted into T3, the active thyroid hormone.

Both the amount of T3 and T4 produced, as well as the conversion from T4 to T3, are key aspects of metabolic function. And, both are heavily influenced by the energetic status of the body.

If the body has a high energy supply and low energy demand, it doesn’t need to conserve energy. So, it runs at full speed, kind of like “high-performance mode.” The thyroid churns out lots of thyroid hormones and the conversion from T4 to T3 works efficiently, allowing for a high metabolism.

But as you read about in part 1 of this series, having a low energy supply and a high energy demand turns on “low-battery mode” to conserve energy. This blocks the release of thyroid hormones and shuts off the conversion from T4 to T3, resulting in a low metabolism.

The relationships between the thyroid, its hormones, and energy balance are integral to the understanding of hypothyroidism. But, the more recently discovered TSH, a hormone produced by the pituitary, has completely changed the way we think about hypothyroidism, for the worse.

TSH, or thyroid stimulating hormone, is produced by the pituitary gland and tells the thyroid to produce more T3 and T4. It does this through a negative feedback mechanism: when T3 and T4 are high in the body, less TSH is produced, and when T3 and T4 are low in the body, more TSH is produced.

So, when T3 and T4 are low, as in the low-energy state, or “low-battery mode,” TSH is generally higher. The opposite is generally true in the high-energy state, or “high-performance mode.”

TSH levels seemed like a good indicator of hypothyroidism based on the above process. So, once it could be easily measured with a blood test, it became the standard diagnostic measure for hypothyroidism. In the meantime, the other symptoms and diagnostic tests became more or less forgotten.

However, TSH is a much less direct measure of thyroid and metabolic status, so it is not as well correlated with thyroid function. For example, infections, caffeine, and chronic stress can all lower TSH, even if the thyroid hormones are low. In other words, your TSH can be within the “normal range,” and you can still be in a hypothyroid state.

This oversight has allowed for two dangerous outcomes:

  1. Many people with hypothyroidism remain undiagnosed because their TSH is within the “normal range”
  2. Hormone replacement medications that contain only T4 (such as Synthroid or levothyroxine) have replaced medications that contained both T3 and T4

How has this reliance on TSH levels led to a change in medications?

The thyroid hormone T4 decreases TSH (remember the negative feedback mechanism). So, taking hormone replacement medications that contain only T4 cause the TSH to go down, which makes it look like the hypothyroidism is improving. But, as you already know, T4 is the inactive thyroid hormone.

So, even though the thyroid may not be producing enough hormones, T4 may not be converted efficiently to T3, and the metabolism may not have increased, it’s still assumed that the T4 medication is working!

But not only is it not working, medications containing only T4 often decrease the metabolism even further by reducing the production of T3. T4 lowers TSH levels, which reduces the amount of T3 and T4 that the thyroid produces. Plus, having a high T4 relative to T3 acts as a signal of low energy, so it inhibits the conversion of T4 to T3 in order to conserve energy.

So, if T4 alone can lower the metabolism even further, causing your symptoms to get even worse, then T4 plus T3 would be the perfect treatment for hypothyroidism, right?

Yes and no. T4 with T3 is much better than T4 on its own. T3 stimulates the metabolism, which increases energy production. This can then allow T4 to convert properly to T3, which will further improve the metabolism and energy supply.

But, here’s the issue: it takes more than just thyroid hormones for energy production to occur, and an increased energy supply is only one part of improving energy balance and hypothyroidism.

Energy imbalance has two components: a relatively high energy demand and a relatively low energy supply.

Energy demands are made up of everything our bodies do that requires energy – digesting food, running on a treadmill, or even just thinking. Energy supply is made up of the energy we produce from food with the help of vitamins, minerals, and other compounds.

Understanding how to increase your energy supply and decrease your energy demand is essential to improving, and even reversing, hypothyroidism. To learn more about how you can improve your energy balance, sign up below for a free 6-part email series on Hypothyroidism, Health, and Energy Balance.


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