Thyroid hormone replacement is the mainstay of treatment for hypothyroidism, whether the hypothyroidism is caused by radiation, surgery, or Hashimoto’s disease (autoimmune destruction of the thyroid gland). The goal is to replace the body’s production of thyroid hormone in the most physiologic way possible. However, a quick internet search will reveal an overwhelming number of options for thyroid hormone replacement. In this article, we will break down the different brands of thyroid hormone available in the US and things to consider before selecting a formulation.
A normal thyroid gland produces 80% T4 (inactive thyroid hormone) and 20% T3 (active thyroid hormone). Various organs have enzymes which convert T4 to T3, which then mediates all the functions of thyroid hormone, from sleep to digestion to temperature regulation.
T4-only formulations:
Generic – Levothyroxine
Brand name – Synthroid, Levoxyl, Euthyrox, Unithroid, Tirosint
These medications are usually the first-line treatment offered. It is important to stay on the same brand or advise your doctor if you are prescribed a different brand than before. Different brands even at the same dose may have slightly different contents.
All these medications are comparable in effectiveness. Tirosint is notable because it comes in a gel capsule or solution form, which can help with medication absorption. Some patients may experience more stable thyroid levels upon switching from generic to brand name hormone.
T3 and T4 combination formulations:
Thyroid extract medications: Armour, NP Thyroid, Nature-Thyroid, WP Thyroid, Westhroid
Synthetic: Cytomel/Liothyronine (T3) plus one of the T4 medications listed above.
Most doctors are reluctant to prescribe thyroid extract medications (which are made from dried and powdered pig thyroid glands) because they do not simulate the normal human thyroid production closely. They tend to contain high concentrations of T3 which can cause highly variable levels and symptoms. Prescribing T3 and T4 as separate pills allows the doctor to control the ratios of each.
A T3-only medication regimen is generally not prescribed.
There are a number of factors that go into selection of a thyroid hormone replacement. Your endocrinologist can talk to you further about which medication is the best choice for you, and why.