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Pharmacy and Medications

Synthroid vs. Armour



I read on another health BBS that a person`s DOCTOR had told her that synthroid "totally completely forever shuts down your own thyroid gland" but that since Armour is a "natural supplement" instead of a "synthetic hormone" it does not have this effect.

I questioned this, and the person referred me to a huge number of web sites that all have very heated debates about the supposed good vs bad effects of synthroid and Armour (and "dessicated thyroid" that can apparently be bought in health food stores thrown into the debate too).

How do I separate Fact from Fiction in all this. I do not know how to tell which is the correct information and which isn`t, and it is all conflicting. A lot of it says that there is some kind of conspiracy between doctors and drug manufacturers and I find that very hard to believe.

But how am I supposed to know WHAT to believe, especially when a lot of the writings claim that my own doctor probably doesn`t have the "Real" info, or even if she did, she wouldn`t be able to tell me??????


Armour Thyroid (desiccated porcine thyroid gland) and Synthroid (levothyroxine) are used as replacement therapy for thyroid hormone when the thyroid is under-active, nonfunctioning, or has been all or partly surgically removed. The thyroid hormones naturally produced in your body are liothyronine (T3) and levothyroxine (T4). These hormones are necessary for metabolic regulation, normal growth, development, and mental function, among other things. T4 is found in the body at approximately four times the level of T3, but T3 is four times more potent. T3 is the active thyroid hormone used in the tissues, whereas T4 is a storage form that is stored in the liver, converted to T3 as needed. This storage mechanism acts as a buffer to help the thyroid keep up with the body’s demand for thyroid hormones. The controversy over whether to use synthetic versions of thyroid hormone (Synthroid, Levoxyl, et al.) versus natural forms (Armour Thyroid) is better stated: “whether to use T4 alone or a T3 and T4 combination.” Armour Thyroid was the only treatment for hypothyroidism for about 50 years, but it was found that the amounts of T3 and T4 varied greatly from batch to batch. Eventually, synthetic T4 (Synthroid) was being produced and widely used because it did not have similar problems of standardization in common with the naturally derived Armour Thyroid. A disadvantage of Synthroid is that some patients do not feel quite as well on T4 alone as they do on T3/T4 combinations. This is thought to be because not all tissues have the ability to convert T4 to T3 equally, such as brain tissue. In order to compensate for this, physicians may over medicate patients with T4 in order to compensate for this conversion problem. This may lead to greatly increased T4 levels, resulting in a temporary hypothyroid condition. Synthetic T4 products have not been shown to produce permanent hypothyroidism, though most patients return to a normal thyroid state soon after stopping the medication. In some patients, combination products may be better than single T4 products, because of a lack of ability to convert T4 to T3. In recent years, a synthetic T3/T4 combination (Liotrix) has been developed to deal with the problem of standardization of the Armour Thyroid. However, Liotrix is more expensive than either Synthroid or Levoxyl, and remains the reason why most therapy for hypothyroidism is initiated with these agents. Prepared by Jed Oyer, PharmD  candidate

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Response by:

Jan Scaglione, MT, PharmD, D.ABAT
Assistant Professor of Pharmacy Practice
College of Medicine
University of Cincinnati