SLOT: Full Definition
What is Armour Thyroid?
Armour Thyroid is a long-standing brand of natural desiccated thyroid (NDT) — a prescription thyroid hormone medication made from porcine (pig) thyroid glands. Each tablet contains both T4 (thyroxine) and T3 (triiodothyronine) in a roughly 4:1 ratio, along with small amounts of T1, T2, and calcitonin. It is one of the oldest thyroid medications still in use, dating back to the late 1800s. Common aliases include branded NDT and porcine thyroid extract.
Armour Thyroid is most often prescribed for Hypothyroidism — particularly hypothyroidism caused by Hashimotos Thyroiditis, thyroidectomy, or Radioactive Iodine Ablation — in patients who do not feel well on T4-only therapy.
How does Armour Thyroid work?
A standard 60 mg (1 grain) Armour tablet contains approximately 38 mcg of T4 and 9 mcg of T3. The T4 portion acts as a steady storage form that the body converts to T3 over hours, while the T3 portion delivers an immediate signal directly to thyroid hormone receptors inside cells. Those receptors regulate metabolism, body temperature, heart rate, mood, cognition, and menstrual cycles.
Because Armour contains active T3, it suppresses TSH more than T4 alone does. For that reason, monitoring requires a complete panel — TSH, Free T4, and Free T3 — alongside how the patient actually feels.
When is it prescribed?
Armour Thyroid is typically considered when:
- A patient has persistent hypothyroid symptoms on Levoxyl, Synthroid, or generic levothyroxine despite normal TSH.
- Labs show poor T4-to-T3 conversion (low Free T3 relative to Free T4).
- A patient prefers a single tablet over separate T4 and Liothyronine.
- After thyroid surgery or RAI when both hormones are needed.
Np Thyroid and Wp Thyroid are alternative branded NDTs with the same general structure.
Patient considerations
Armour Thyroid is taken once daily — sometimes split — on an empty stomach, away from coffee, calcium, iron, magnesium, and biotin, all of which interfere with absorption. Side effects almost always reflect too much T3: palpitations, anxiety, jitteriness, insomnia, tremor, sweating, headaches, and unintended weight loss. Over the long term, over-replacement can contribute to bone loss and atrial fibrillation, especially in postmenopausal women. Armour is not appropriate for untreated adrenal insufficiency, uncorrected hyperthyroidism, or unstable cardiac disease, and it requires careful management in pregnancy.
Because Armour is pork-derived, it is not suitable for vegetarians, vegans, or patients with religious restrictions on pork. Some patients also report that reformulations over the years have changed how they feel — switching to NP Thyroid or compounded NDT can sometimes help.
At Modern Thyroid Clinic, Armour is one tool among many. The goal is matching the right medication strategy to the right patient, then refining it through symptoms and labs over time.
Common symptoms
Common questions
How is Armour Thyroid dosed compared to levothyroxine?
One grain (60 mg) of Armour contains roughly 38 mcg of T4 plus 9 mcg of T3. Because T3 is more potent than T4, the equivalence is not a clean conversion. A common rule of thumb is that 60 mg of Armour replaces somewhere between 75 and 100 mcg of levothyroxine, but actual response varies. Switching between Armour and T4-only therapy should always involve a full lab recheck about six weeks after the change, with adjustments based on symptoms.
Is Armour Thyroid the same as NP Thyroid?
Both are natural desiccated thyroid made from porcine glands and both contain T4 and T3 in a similar ratio, but they are different brands made by different manufacturers with different inactive ingredients. Some patients tolerate one better than the other. Reformulations and supply issues over the past decade have led many patients and clinicians to switch between Armour, NP Thyroid, and WP Thyroid. The active ingredients are comparable, but how a tablet feels day to day can differ.
Can I take Armour Thyroid during pregnancy?
Thyroid hormone needs rise quickly in early pregnancy, and untreated hypothyroidism can affect fetal development. Most obstetric and endocrine guidelines recommend levothyroxine (T4) as the preferred medication during pregnancy because T4 crosses the placenta well and dosing is easier to standardize. Some women on Armour transition to T4 — sometimes with a small T3 — when pregnancy is planned or confirmed. The decision should be made with your clinician based on labs, symptoms, and individual history.
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