Dr. Tan, can you explain the difference between Armour Thyroid and Synthroid or Levothyroxine? Do you have a preference between the two?
First, some background. The thyroid gland produces different types of thyroid hormone, the most important of which are T4 and T3. T4 makes up the majority of thyroid hormone made by our thyroid glands, it is weaker and is considered to be a "reserve" form of the hormone. T4 is converted into T3 (which is considered to be more potent or active) in peripheral tissue such as the liver, kidney and intestines. Nature is very wise to do this--because it makes sense for the body to produce more of a weaker hormone and have it in "reserve" and then later on have it converted in to the more active type of hormone later on, when needed.
Synthroid, levothyroxine, levothroid are all different medication names for T4. These are the most widely prescribed type of thyroid medication, usually by endocrinologists. The assumption is that the person taking these medications are able to convert T4 (reserve form) to T3 (active form) efficiently. The benefits of taking plain T4 is that it is stable, it has a long half life, and patients would often not feel a major difference if they do not take their dose at exactly the same time everyday.
Armour Thyroid is made from dried pig thyroid gland and therefore contains both T4 and T3 naturally. The ratio of T4 and T3 in Armour Thyroid is similar to human thyroid hormone output, but not exactly the same. The benefit of taking Armour Thyroid is that it naturally contains T3 (active form) already and may be helpful for people who do not convert T4 to T3 well (there may be several reasons for this including nutritional deficiencies). The downside is that if a patient skips a dose, they will feel more than if they were taking plain T4 because the T3 component of Armour Thyroid is more potent and it also has a shorter half-life in the body. Nature-Throid, West-Throid are other brand names of T4/T3 combination thyroid medications.
Do I have a preference? Armour Thyroid seems to make more sense to me than plain T4 because it more closely resembles how our body naturally produces thyroid hormone--which is a combination of both T4 and T3. However, some patients may have problem taking a medication sourced from pigs/animals; in these situations, if a patient is NOT doing well on Synthroid/Levothyroxine/Levothroid despite normal TSH levels, and need some T3, I may add in some Cytomel which is a pharmaceutical form of T3 to augment the T4.
Lately, I have been switching my most sensitive patients to a combination of Levothyroxine (T4) with an additional dose of Cytomel (T3--the more active type of hormone). The ratio I start with approximates the amount of T4 and T3 that a healthy person would make naturally. Cytomel is available as regular prescription (from Walgreens or CVS for example) or as a compounded time-release form (so that it lasts longer in the body, and you avoid the "peak then valley" associated with medicines that have a shorter half-life).