Thyroid hormone helps deliver oxygen and energy to your cells, tissues, and organs, and is essential for every bodily function. Hypothyroidism refers to the condition where you have insufficient levels of thyroid hormone.
Hypothyroidism has a number of causes, including:
- Autoimmune Hashimoto’s thyroiditis
- Radioactive iodine treatment (RAI) for Graves’ disease/hyperthyroidism
- Surgical removal of your thyroid gland to treat thyroid cancer, hyperthyroidism, nodules, or goiter
- Congenital hypothyroidism — born without a gland, or born with an underactive thyroid
- Iodine deficiency
Less commonly, there are medications, including lithium, that can cause hypothyroidism.
No matter how you become hypothyroid, once you do not have enough thyroid hormone, you need prescription thyroid hormone replacement treatment.
The goal of thyroid hormone replacement treatment is to replace the missing hormone with medication.
There are several different medications used to treat hypothyroidism, including:
- Levothyroxine (synthetic T4)
- Liothyronine (synthetic T3)
- Natural desiccated thyroid (NDT)
Thyroid hormone replacement medication is taken daily with care to follow guidelines and cautions to avoid interference from foods, supplements, and medications.
A normal thyroid gland produces several hormones, including thyroxine (T4) and triiodothyronine (T3). The vast majority of hormone produced is T4, which is a storage hormone. It goes through a transformation in the body — and loses a molecule of iodine — to become the active hormone, T3. This process is called T4-to-T3 conversion.
Conventional medicine assumes that the T4-to-T3 conversion process works well for everyone. As a result, most physicians recommend the synthetic form of the T4 hormone as a treatment for hypothyroidism. The assumption is that the synthetic T4 hormone will effectively convert into T3 in the body of the thyroid patient.
Synthetic T4 is known generically as levothyroxine, l-thyroxine, or L-T4. Some brand names of levothyroxine include Synthroid, Levoxyl, and Tirosint.
Generic levothyroxine, Synthroid, and Levoxyl are all available in tablet form. The tablets from the different brand name and generic manufacturers have different fillers and dyes, so patients may respond to them differently. Also, Synthroid contains two common allergens: acacia (a derivative of tree bark) and lactose. These ingredients can trigger allergic responses in sensitive patients.
Tirosint is a specially-formulated, hypoallergenic liquid, gel-cap version of levothyroxine created for people with allergies to dyes and fillers, or who have absorption problems due to conditions like Crohn’s disease or irritable bowel syndrome.
Liothyronine (synthetic T3)
Research shows that some patients feel better with the addition of a second drug to levothyroxine therapy. This second drug is liothyronine, a synthetic form of the T3 hormone.
Some physicians — especially integrative practitioners and those with expertise in hormone balance — theorize that genetic differences, nutritional deficiencies, stress, and other factors make some patients less effective at T4-to-T3 conversion. As a result, when these patients rely on levothyroxine alone for hypothyroidism treatment, they are not able to convert enough T4 into active T3 to resolve symptoms. Adding T3 to the levothyroxine — known as T4/T3 combination treatment — can help resolve symptoms for many of these thyroid patients.
A manufactured tablet form of liothyronine is available as a generic drug, and also as a brand-name drug called Cytomel.
Because liothyronine is very short-acting and can be stimulating, some patients find they are better able to tolerate a specially prepared, time-released form of the drug. Time-released liothyronine — also known as sustained-released or slow-release T3 — is a prescription drug available only from compounding pharmacies.
Note: The use of T3 as part of hypothyroidism treatment is controversial. Some physicians test for and treat low T3 levels, but others refuse to prescribe T3, and only treat hypothyroidism with levothyroxine.
Natural desiccated thyroid
Natural desiccated thyroid (NDT) — the first effective drug treatment for hypothyroidism — was introduced in the early 1900s. The first NDT drug, Armour Thyroid, was prepared from the dried thyroid gland of pigs. Armour was the only hypothyroidism treatment available until levothyroxine was introduced in the 1950s.
Currently, a generic NDT drug is available, NP Thyroid. There are also two hypoallergenic brand-name NDT drugs: Nature-throid and Thyroid WP.
Because NDT was on the market before the creation of the U.S. Food and Drug Administration (FDA), the drug was “grandfathered in” and never required to go through a full FDA application and review process. It continues to be an FDA-regulated drug, and it's legal for physicians to prescribe NDT for hypothyroidism treatment.
Because NDT contains actual thyroid gland in a dried form, it contains natural forms of both the T4 and T3 hormones. It also contains some other thyroid hormones such as T1, T2, and T3, the functions of which are not well-known or understood by physicians.
Some patients and practitioners find that hypothyroidism symptoms are better resolved on NDT, compared to levothyroxine-only, or T4/T3 combination treatment. There is no definitive research that explains, however, why a subset of patients prefers NDT or appear to have a better response to NDT compared to synthetic thyroid medications.
Some patients take other medication combinations — including NDT with levothyroxine, or NDT with liothyronine — for the best relief of their symptoms.
Note: Prescribing NDT is controversial. Some physicians consider it old-fashioned, outdated, and inferior to levothyroxine and refuse to prescribe it as a hypothyroidism treatment.
What is the best thyroid hormone replacement medication?
The best thyroid hormone replacement medication is the medication that works best and safely … for you. Keep in mind that it is often a trial-and-error process to determine which drugs, manufacturers, dosages, and timing will safely and best relieve your hypothyroidism symptoms.