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Illustration highlighting the thyroid gland.

The most commonly used medication in Thyroid Hormone Replacement Therapy is Levothyroxine (T4).

For many people with hypothyroidism (underactive thyroid), supplementing with T4 is enough to boost thyroid hormone levels. This is because the body converts T4 to its more active counterpart, T3.

However, some patients have difficulty metabolizing T4 into T3.

In this case, hypothyroid symptoms will persist, because the body can’t fully utilize the supplemented T4.

When this occurs, patients may need to include Liothyronine (T3), or use a desiccated thyroid medication that includes both T3 and T4.

T4 Conversion and Genetics

Studies have found a genetic source for the different ways bodies utilize T4. The gene has been identified as DIO2 (IDII).

Depending on this gene, patients may struggle to convert their stores of T4 to T3.

In addition to a T3 deficiency, an inability to convert T4 to T3 also causes overproduction of a substance called Reverse T3 (RT3). Too much RT3 can further impact thyroid function, leading to a cycle of hypothyroidism that is potentially made worse by supplementing T4 alone.


How Do You Diagnose This Issue?

Comprehensive testing is crucial to successfully diagnosing and treating hypothyroidism.

Some clinics only require a few thyroid tests, but these typically don’t paint the full picture. When it comes to T4 metabolism, a complete panel is the best way to understand how thyroid hormones are utilized in the body.

We recommend these thyroid blood tests:

This measures how much T3 is floating freely in the blood.

This measures how much T4 is floating freely in the blood.

RT3 is a byproduct of T4 metabolism. If your body has trouble converting T4 to T3, your RT3 levels will likely be abnormally high.

Measuring thyroid antibodies helps determine whether your hypothyroid symptoms stem from an immune issue.

Thyroglobulin is a thyroid protein, and antibodies indicate an autoimmune condition.

Along with comprehensive testing, individualized care is important for treating thyroid disease.

You and your provider should work together to come up with a treatment plan and adjust as necessary to optimize your results. Ongoing follow-ups and blood testing can help you see how your body is responding to treatment over time.

Thyroid Medication Options

If you’re diagnosed with hypothyroidism and have difficulty converting T4 to T3, you have several medication options. Each patient is individual and may respond differently to treatment.

  • Synthetic Thyroid Hormones 

    As we’ve discussed, synthetic hormones are one option for thyroid disease treatment. T3 comes in the form of Liothyronine, and T4 comes in the form of Levothyroxine.

    Synthetic hormones are biologically identical to natural thyroid hormones, meaning they have the same chemical structure and perform the same function.

    Depending on how you respond, you may need both medications or Liothyronine (T3) as a monotherapy.

  • Desiccated Thyroid Hormone

    Another thyroid disease option is desiccated medication. “Desiccated” refers to the drying and powdering process of natural material. Most of the time, desiccated thyroid hormone medication is made from the thyroid glands of pigs.

    Desiccated thyroid hormone typically contains a mix of T3 and T4 and may be more suitable for patients who struggle to utilize T4.

Thyroid Supplements

In addition to Thyroid Hormone Replacement Therapy, you may want to add supplements that support thyroid health.

Iodine is a common thyroid supplement, because the thyroid produces its hormones from iodine.

Quality iodine supplements include:

  • i-Throid, which contains a blend of iodine and free elemental iodine for best effects.
  • Life Extension Sea Iodine, which includes a blend of organic iodine from marine algae to provide superior supplementation.

You should supplement iodine under the supervision of a provider to ensure you don’t over-supplement this important mineral.

I-throid and Sea Iodine thyroid supplement bottles for thyroid disease treatment

Thyroid Hormone Replacement Therapy with Defy Medical

Defy Medical offers individualized care, in-depth consults, access to lab testing, and a full range of thyroid medications. We often treat thyroid patients who have tried traditional thyroid care and failed to find relief.

If you’re struggling with a thyroid condition or potential hypothyroid symptoms, Defy Medical can help you pinpoint the issue and treat it, so you feel better, have more energy, and improve metabolism health.

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