Armour Thyroid vs Synthroid (Levothyroxine) Conundrum
Armour Thyroid vs Synthroid (Levothyroxine) Conundrum
Hypothyroidism, or underactive thyroid, is a common thyroid disorder that results in symptoms of decreased metabolism (Read more on Hypothyroidism). Levothyroxine and Armour Thyroid (desiccated Thyroid extract) are two common forms of thyroid hormone hormone replacement used to treat hypothyroidism. At this time only Levothyroxine is FDA approved.
What is Armour Thyroid or Desiccated Thyroid extract?
The main aim of this article is to educate and explain the difference between synthetic and desiccated thyroid hormone extract. You may have come across some products marketed as “Natural Thyroid hormone”, and probably had so many questions on what form of thyroid hormone replacement is best for you. Today we are going to go dive deep into the history and science behind some of these products compared to the synthetic type of thyroid hormone.
Desiccated thyroid extract is a dried animal thyroid (porcine/pig) extract first described and used in the late 19th century (1891) for treatment of hypothyroidism. Most people who suffer from hypothyroidism have been struggling to understand the difference between Desiccated thyroid extract and synthetic thyroid hormone. Most endocrinologists will tell you that almost everyday they get a question on Armour thyroid. The most common scenario is someone who has done some research on these products and wants to try a “Natural Thyroid hormone” alternative. Current practice guidelines recommend synthetic thyroid hormone (Levothyroxine) as a first line treatment for hypothyroidism. These guidelines also recognize that there is limited evidence to recommend for or against desiccated thyroid hormone extract as a preferred treatment. The FDA has called for further studies on “natural thyroid hormone extract” and so far there has been just a few studies comparing the two. What exactly does this mean for those interested in this product? In order to fully understand how we got here lets take a stroll down memory lane.
History of Armour
In the late 19th century, physicians had to rely on their clinical acumen (patient’s symptoms and examination findings) to diagnose hypothyroidism. In 1891 an English physician by the name of George Redmayne Murray first described success in treating myxedema (severe hypothyroidism) with injections of porcine (pig) thyroid extract. This discovery led to the widespread use of desiccated thyroid extract in treating hypothyroidism into the 20th century. One of the common brands of desiccated thyroid hormone extract is Armour Thyroid, named after Armour and Company, a dominant American meatpacker in the 20th century. In early 20th century it was difficult to assess thyroid hormone levels and composition in the human body, until after 1960s when commercial labs were available to test thyroid hormone levels. Ever since then we have been able to test and analyze thyroid hormone levels and the manner in which they are metabolized.
Towards the end of the 20th century more formulations of the Desiccated thyroid extract were made available by different companies. Some of these formulations include NP-Throid, WP-Thyroid, and Westhroid. Besides these brands there are other compounds which are marketed as supplements, however some of these were found to have some active thyroid hormones in them. This has resulted in inappropriate use or abuse of these medications in some clinics when used for weight loss and unexplained fatigue. serious and sometimes life-threatening conditions have been reported with inappropriate use of thyroid hormone supplements in patients who had normal function thyroid.
Historically, treatment of hypothyroidism with Desiccated thyroid was successful, so why did we move away from this form of treatment? We know that scientific discoveries have lead to more advanced and better ways of treating most conditions. well hypothyroidism is no exception. Around the mid 20th century a synthetic thyroid hormone, L-thyroxin, was synthesized and later purified to a structure very similar to our own thyroid hormone. This meant less variability in the hormone composition and levels more predictable than its primitive counterpart. Under normal conditions we produce two forms of thyroid hormones (T4 and T3) in a ratio of 10:1 respectively and in a pig’s thyroid the ratio is 11:1, respectively. Of the two hormones, T3 is the active form and T4 is converted to T3 by an enzyme called Deiodenase 2. The human body converts T4 to T3 especially on demand, except for a very few situations where there is lack of this Deiodenase enzyme to activate T4.
Difference between the two forms of Thyroid hormone
A study published in The Journal of Clinical Endocrinology and Metabolism in 2013 found that thyroid hormone extract use was associated with more weight loss than Levothyroxine. In the study almost half of patients preferred thyroid hormone extract than Levothyroxine. However there was no difference in the psychometric testing and symptoms between the two forms of treatment.
It is essential to understand that thyroid hormone can have deleterious effects if exceeding normal physiologic levels. One of these effects is increased heart rate in some people, which maybe attributed to the T3 component of this preparation. I take it you already see where this is going, and yes that’s where most of the scrutiny on Armour/desiccated thyroid comes from. Here is a direct comparison of the two forms of thyroid hormones:
Similarities:
Both have similar efficacy when titrated to right thyroid levels. As long as the Thyroid stimulating hormone (TSH) is kept normal.
Cost – both are within a comparable price range with slight difference between brands.
Symptom relieve – there is no clinical evidence to suggest a difference between the two (most of the observed difference in clinical practice is subjective and varies from person to person).
Both have the same Half-life of about 7 days (the time it takes for half of the dose to be metabolized and eliminated from the blood stream).
They are both available by prescription only
Differences:
FDA approval – only levothyroxine is approved whereas Desiccated thyroid hormone extract is not
Levothyroxine has less variability in composition than desiccated thyroid (brand to brand and even batch to batch variability)
Because of T3 in desiccated thyroid some people may have more cardiac (heart) side effects than with Levothyroxine. T4 which is easily converted to T3 at the body’s normal metabolic rate and demand.
Levothyroxine (Synthroid) has a generic available whereas desiccated thyroid is only available as a brand.
Levothyroxine delivers only T4 whereas Armour/desiccated thyroid extract has a blend of both T3/T4 in a ratio of 4:1. In some people T3 may provide better symptom relieve than just T4 alone, however the evidence is not strong enough.
Dose Forms: Levothyroxine has multiple color-coded dose forms which makes it easier to make small changes in dosing (e.g. 25, 50, 75, 88, 100 etc.), whereas most Desiccated thyroid extracts have wide dose ranges. Hence sometimes may require a mix of dose forms to achieve the desired dose.
Conclusion
We now have a general understanding of what these two popular medications for hypothyroidism are. As to which one is better there is no scientific evidence thus far, however there has been a study showing slight difference in weight loss with Desiccated thyroid extract and close to half of the participants who prefer Armour thyroid compared to Levothyroxine. More studies are still needed to identify those who might benefit from desiccated thyroid extract. The American thyroid association recommends Levothyroxine as first line treatment for hypothyroidism.
What we recommend:
As a practicing Endocrinologist I usually sit down with my patients and discuss all these facts in great detail. I believe both options should be left on the table as long as there is no contraindication. Whichever treatment is started the goal is to normalize the thyroid hormone levels. If at any point a decision is made to switch to the other form of treatment, a proper calculation of the equivalent dose should be done and then followed up with thyroid blood test in 6 weeks to ensure proper dosing. Its very important that you discuss these facts with your doctor. For Armour thyroid, its strongly recommended to find a doctor with experience in using this formulation. We generally follow a test called Thyroid stimulating hormone (TSH) rather than the actual thyroid hormones since they tend to be unreliable.
