Low T3 and treatment of hypothyroidism


Hypothyroidism is when your body doesn’t have enough thyroid hormone, a crucial substance that helps regulate how your body uses energy.

This condition can be due to a problem with the thyroid gland or other parts of the body that control the thyroid gland.

There can be many reasons why someone’s thyroid isn’t working correctly, including problems with how the hormone is transported around the body, how it’s used inside cells, or how it connects to places where it’s needed.

Interestingly, some people with severe hormone deficiency might have few or no symptoms at all, while others with only a slight deficiency might have a lot of symptoms.

But remember, the symptoms that make you think of an underactive thyroid can be vague and could be due to other health issues that have nothing to do with your thyroid.

Endocrinologists often recommend a medication called levothyroxine for people with an underactive thyroid because it works well, it’s been used safely for many years, it doesn’t usually cause side effects, it’s easy to take, and it is affordable.

Thyroxine (also known as T4), the hormone that’s low in people with hypothyroidism, doesn’t get into the body well on its own when taken as a pill.

Rationale for levothyroxine therapy

So, how did we achieve safe oral versions of natural thyroid hormone?

Scientists have figured out that by substituting one hydrogen ion on natural thyroxine (also known as T4) with sodium, a more stable form of T4 is produced that the body can use better.

This manufactured version of T4, known as levothyroxine, is the same as the natural hormone, except for this tiny change.

Once you take levothyroxine, it gets into your bloodstream quickly from the upper part of your small intestine and lasts for quite a while – about 5 to 7 days. We refer to this as the half-life.

So, if you start taking levothyroxine or if a physician changes your dose, it takes about 5 to 6 weeks for the levels in your blood to get stable.

This is because a fundamental principle of pharmacology is that it takes about 4 to 5 half-lives for a drug to reach a study state.

Since the half-life of levothyroxine is about a week, waiting approximately 5-6 weeks to assess a biochemical response to treatment is scientifically sound. In essence, checking your thyroid labs earlier than this may not provide very reliable test results.

Forms of thyroid hormone

Liquid thyroid medicine is often absorbed by the body more reliably than pill forms, especially for people with thyroid issues who also have digestive problems or are taking certain stomach acid-lowering medications.

Like a synthetic version of the thyroid hormone, T4, there is also an artificial form of another thyroid hormone called T3.

The synthetic version of T3, liothyronine, is just like the T3 that your own thyroid makes.

Next, there is a compound called desiccated thyroid extract, which graphically is made by drying and grinding up pig thyroid glands.

Desiccated thyroid extract has both of the thyroid hormones in it.

Mostly T4 and a little less T3 – kind of like having four scoops of T4 to every one scoop of T3.

But, the exact mix can change a bit between different brands or batches (within the same brand).

Some alternate healthcare practitioners recommend using desiccated thyroid extract as a “natural” way to treat thyroid problems because it comes from animal glands and is not made in a lab.

But there’s a catch: pig thyroids, which are usually used to make desiccated thyroid extract, don’t work exactly like human thyroids do.

For instance, our thyroid produces a lot more T4 compared to T3—like 14 parts of T4 to every part of T3.

Well, pig thyroids, on the other hand, have a lot more T3—about 4 parts of T4 for every part of T3.

So when you take desiccated thyroid extract, you get a much bigger dose of T3 than your body is used to, which can make the T3 level in your blood shoot up quickly, sometimes even more than what is considered normal.

And even though this spike in active thyroid hormone might not last very long, this sudden surge of T3 could potentially be harmful, either right away or over time, just like any situation where you have too much thyroid hormone in your system.

This can increase your risk for an abnormal heart rhythm and bone loss.

Next, Custom-mixed thyroid medications from special compounding pharmacies offer a mix of two types of thyroid hormones (T4 and T3) for those who prefer them.

But because these mixtures can vary a lot and aren’t standardized, it’s generally not advised to use them.

So how about using only liothyronine (also known as T3)

Using only active thyroid hormone, that is, T3 as sole treatment for hypothyroidism, is not advisable because it doesn’t mimic the body’s natural processes.

Indeed, taking T3 just once a day can lead to wide swings in the levels of the hormone in the blood.

There are special slow-release forms of T3 being developed that don’t cause these fluctuations, but these aren’t yet approved by the FDA in the United States.

These may become potential options for research into treatments that combine T3 with T4.

Endocrinologists follow expert advice from leading health organizations based on the available robust evidence.

When can combination T3 and T4 be considered?

It is best to stick with the standard treatment, which is levothyroxine. Some have suggested adding another thyroid medicine called liothyronine, but the experts, including the American Thyroid Association (ATA), the American Association of Clinical Endocrinologists (AACE), and the European Thyroid Association, don’t recommend this combination for everyone.

Based on the evidence gathered from detailed studies and reviews, there needs to be stronger proof that taking both T3 and T4 works better than just T4 alone.

Furthermore, we are not so sure if using both T4 and T3 together is safe in the long run.

So is there a time when we can consider combination treatment of even dessicated thyroid extract?

This is a delicate question.

There are indeed special cases where it makes sense to try dissicated thyroid extracts or other combination T4 with T3.

This could be for people who still feel the symptoms of an underactive thyroid even though they’re taking the standard T4 medication at the right dose with normal thyroid labs.

Normal thyroid labs refer to an assessment of TSH with or without T4.

Reverse T3, thyroid peroxidase antibody, and free T3 levels are not recommended for monitoring hypothyroidism treatment. We will discuss the rationale for this in a future video.

If you decide to attempt either desiccated thyroid extract or combination treatment, careful monitoring will be important because too much thyroid hormone can be harmful to the human body.

I hope you found today’s topic informative. 



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The MyEndoconsult Team. A group of physicians dedicated to endocrinology and internal medicine education.

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