Prescribing Armour Thyroid (Desiccated Thyroid Extract)
Armour Thyroid should generally not be used as first-line therapy for hypothyroidism; levothyroxine (synthetic T4) remains the standard of care due to its predictable pharmacokinetics, standardized dosing, and FDA oversight. 1, 2 However, for the subset of patients who remain symptomatic despite biochemically adequate levothyroxine therapy, a trial of desiccated thyroid extract (DTE) may be considered after exhausting combination synthetic therapy (LT4+LT3). 2, 3
When to Consider Armour Thyroid
Patient Selection Criteria
Reserve DTE for levothyroxine-unresponsive patients only - those who have persistent hypothyroid symptoms (fatigue, cognitive dysfunction, mood disturbances) despite normalized TSH on levothyroxine monotherapy. 2, 3
First attempt combination synthetic therapy (LT4+LT3) before considering DTE, as this provides more precise dosing control and better standardization. 2
Consider DTE as a trial option when patients have failed both levothyroxine monotherapy and synthetic combination therapy, with documented persistent symptoms affecting quality of life. 3
Critical Exclusions
Avoid in patients with cardiac disease, atrial fibrillation, or elderly patients (>70 years) due to the risk of T3-induced cardiac complications from the supraphysiologic T3 peaks that occur after DTE absorption. 1, 4, 5
Never use in patients taking testosterone or anabolic steroids - the combination creates a synergistic hypercoagulable state with documented risk of myocardial infarction even in young patients without traditional cardiovascular risk factors. 4
Contraindicated in patients with recent acute coronary syndrome or unstable cardiac conditions due to T3's effects on cardiac metabolism and oxygen demand. 4
Dosing Protocol for Armour Thyroid
Initial Dosing Strategy
Start with 30 mg (½ grain) daily for patients transitioning from levothyroxine, taken as a single morning dose on an empty stomach. 5, 2
For newly diagnosed hypothyroidism, start with 15-30 mg daily and titrate slowly, though levothyroxine remains strongly preferred for treatment-naive patients. 1, 2
The typical maintenance dose range is 60-180 mg daily (1-3 grains), with most patients requiring 60-120 mg. 6, 3
Conversion from Levothyroxine
Approximate conversion ratio: 100 mcg levothyroxine ≈ 60 mg (1 grain) Armour Thyroid, though this is imprecise due to the T4:T3 ratio of approximately 4:1 in DTE versus the body's natural production. 2
Reduce levothyroxine dose by 50-75% when initiating DTE to avoid transient hyperthyroidism during the transition period. 5, 2
Monitor closely during conversion as the T3 component causes more rapid symptom changes than levothyroxine alone. 5
Dose Titration
Increase by 15-30 mg increments every 6-8 weeks based on TSH, free T4, and free T3 levels, along with clinical response. 1, 2
Target TSH should remain in the reference range (0.5-4.5 mIU/L) to avoid risks of subclinical hyperthyroidism including atrial fibrillation and bone loss. 1, 2
Expect free T3 levels in the upper half of the reference range or slightly elevated 2-4 hours post-dose due to the T3 absorption peak, but trough levels (pre-dose) should remain within normal limits. 6, 5
Monitoring Requirements
Initial Monitoring Phase
Check TSH, free T4, and free T3 every 6-8 weeks during dose titration until stable therapeutic levels are achieved. 1, 2
Measure thyroid function tests in the morning before the daily dose to assess trough levels and avoid misinterpretation of post-absorption T3 peaks. 6, 5
Monitor heart rate and blood pressure at each visit during the first 3-6 months, as T3 can cause tachycardia and hypertension. 4, 5
Long-Term Monitoring
Once stable, check TSH and free T3 every 6-12 months or sooner if symptoms change, as DTE content can vary between batches despite manufacturer oversight. 1, 2
Annual ECG for patients >60 years or with any cardiac risk factors to screen for atrial fibrillation, which occurs more frequently with T3-containing preparations. 1, 4
Monitor bone density in postmenopausal women if TSH remains <0.5 mIU/L, as even mild TSH suppression increases fracture risk. 1, 2
Critical Safety Considerations
Unique Risks of Desiccated Thyroid
Lack of FDA standardization oversight - DTE remains outside formal FDA regulation, with consistency of T4 and T3 content monitored only by manufacturers, creating potential for batch-to-batch variability. 2
Supraphysiologic T3 peaks occur 2-4 hours post-dose, reaching levels that may exceed the reference range and cause palpitations, anxiety, or tremor even when trough levels are normal. 6, 5
The fixed T4:T3 ratio of 4:1 in DTE does not match the body's natural production ratio, potentially leading to relative T3 excess or T4 deficiency in some patients. 2
Drug Interactions and Absorption Issues
Separate DTE from calcium, iron, proton pump inhibitors, and bile acid sequestrants by at least 4 hours as these interfere with thyroid hormone absorption. 1
Avoid concurrent use with sympathomimetics or stimulants due to additive cardiovascular effects from the T3 component. 4, 5
Recent iodine exposure (CT contrast) can transiently affect thyroid function - delay DTE initiation for 6-8 weeks after iodinated contrast administration. 1
When to Discontinue DTE
Stop immediately if TSH falls below 0.1 mIU/L and reduce dose, as severe TSH suppression significantly increases atrial fibrillation risk (5-fold in patients >45 years). 1, 2
Discontinue if patient develops cardiac symptoms (chest pain, palpitations, new arrhythmia) and transition back to levothyroxine monotherapy. 4, 3
Consider stopping if no symptomatic improvement after 6 months of adequate dosing with normalized TSH, as continued use exposes patients to risks without benefit. 3
Evidence Quality and Clinical Context
Supporting Evidence
One observational study of 400 patients followed for mean 9 years showed no increased mortality or cardiovascular morbidity with DTE compared to levothyroxine after age adjustment, though this was not a randomized trial. 2
A consecutive case series of 31 patients demonstrated significant improvement in quality of life scores (EQ-5D-5L utility increased by 0.392, p<0.001) and thyroid symptom scores after 6 months on DTE. 3
Bioavailability studies confirm T3 absorption from DTE is equivalent to synthetic T3, with no difference in time course or extent of absorption whether T3 is given as synthetic hormone or as part of thyroglobulin. 6
Critical Limitations
No large randomized controlled trials compare DTE to levothyroxine for patient-important outcomes like quality of life or mortality. 2
The 2000 FDA approval process for levothyroxine did not include studies evaluating long-term adverse effects, and similar rigorous safety data are lacking for DTE. 1
Most evidence supporting DTE comes from observational studies and case series rather than controlled trials designed to assess efficacy and safety. 2, 3
Common Pitfalls to Avoid
Never initiate DTE in treatment-naive hypothyroid patients - levothyroxine remains first-line therapy with decades of safety data and predictable pharmacokinetics. 1, 2
Do not use TSH alone for monitoring DTE therapy - always measure free T3 to detect excessive T3 levels that may occur despite normal TSH. 5, 2
Avoid dosing DTE twice daily despite T3's short half-life, as this increases the frequency of supraphysiologic T3 peaks and patient burden; once-daily dosing is standard. 5, 3
Never combine DTE with testosterone or anabolic steroids due to documented risk of thrombotic events including myocardial infarction in young patients. 4
Do not assume all DTE products are equivalent - different manufacturers may have varying T4:T3 ratios and bioavailability, requiring dose adjustment when switching brands. 2
Failing to counsel patients about the 2-4 hour post-dose T3 peak can lead to unnecessary dose reductions when patients report transient palpitations or anxiety that resolve spontaneously. 6, 5