Switching to Armour Thyroid

Question: A number of my patients are interested in switching to Armour Thyroid. What concerns do you have about this from a pharmacist perspective? - A CHC Provider

Answer: The 2014 American Thyroid Association guidelines state “levothyroxine should remain the standard of care for treating hypothyroidism. We found no consistently strong evidence for the superiority of alternative preparations (e.g., levothyroxine–liothyronine combination therapy, or thyroid extract therapy, or others) over monotherapy with levothyroxine, in improving health outcomes.”

About Armour Throid and other desiccated animal thyroid products:

• Armour Thyroid contains levothyroxine (T4) and liothyronine (T3), plus other molecules the thyroid gland secretes. Although desiccated animal thyroid extract may sound attractive as an option for patients who like to take natural remedies, there is no data that these other substances meet human needs, maintain activity in the preparation, survive the GI tract, or reach adequate blood levels.

• Armour Thyroid may provide too much liothyronine and lead to hyperthyroid effects (atrial fibrillation, osteoporosis, etc.) as the ratio of T3 to T4 in these preparations can be almost four times higher than is secreted by the human thyroid, and may vary from each.

• It may also not provide enough T4, and might reduce serum T4 levels by upregulating T4 to T3 conversion.


• Using liothyronine monotherapy is not recommended. If having difficulties in achieving a euthyroid state with levothyroxine monotherapy, first look for problems with nonadherence, incorrect administration, or interactions. If none identified, liothyronine could be added to levothyroxine in patients who remain symptomatic despite normal TSH levels, usually after an adequate trial of levothyroxine (e.g. 3-6 months), and ruling out other causes (e.g. psychiatric illness, autoimmune disease, anemia).

• The natural human T4:T3 ratio is 14:1, therefore levothyroxine to liothyronine ratios between 13:1 to 20:1 should be used. E.g. If pt is taking levothyroxine 100 mcg, could be switched to 88 mcg of levothyroxine and 5 mcg of liothyronine.
• Give liothyronine BID- may need to split tablets do this. If the dose cannot be divided evenly, give the larger dose at bedtime.


Normal TSH, normal free T4, and normal free T3


• These should be checked 6-8 weeks after starting combo therapy, with a blood draw before the AM doses are taken.

o The following labs may vary by laboratory and assay used. Refer to laboratory provided reference range, which usually fall within the ranges below.

 T4 serum concentrations: Adults: ~4 to 12 mcg/dL ; Pregnancy: ~5.5 to 16 mcg/dL
 Free T4: Adults: 0.7 to 1.8 ng/dL
 Total T3: Adults: 80 to 230 ng/dL
 TSH: 0.45 to 4.12 milliunits/L

• High T3 levels during the absorption phase can be associated with arrhythmias and nervousness. Use with caution in elderly patients; they may be more likely to have compromised cardiovascular function.
• Increase dose slowly and monitor for s/sx of angina.
• If a dose adjustment is needed, adjust only 1 component of the combo at a time. E.g. if T3 level is low, or T4 level is high, increase the liothyronine dose only.
• A 3 month trial of the combo is reasonable to see if improvement of hypothyroid symptoms occurs.
• Long-term risks of combination therapy, such as fractures and CV events, are unknown. Only once daily dosing of levothyroxine has long-term outcomes data that support its use.

References: Pharmacist Letter, UptoDate, and Guidelines for the Treatment of Hypothyroidism. Thyroid. 2014;24(12):1670-1751.

Natalia Uzal, PharmD
Clinical Pharmacist