Natural Desiccated Thyroid (Armour/NP Thyroid) — Thyroid Hormones
Porcine-derived thyroid hormone containing T4, T3, T2, and T1. FDA-approved. Preferred by some patients over synthetic T4.
Overview
Natural desiccated thyroid (NDT) is derived from the thyroid glands of pigs and contains a mixture of thyroid hormones including T4, T3, T2, T1, and calcitonin in physiological ratios. Brand names include Armour Thyroid (Allergan), NP Thyroid (Acella), and Nature-Throid/WP Thyroid (RLC Labs). NDT was the original treatment for hypothyroidism before the advent of synthetic levothyroxine in the 1960s and has been in continuous use for over 100 years. Each grain (60 mg) of NDT contains approximately 38 mcg T4 and 9 mcg T3, providing a T4:T3 ratio of approximately 4.2:1, which is higher in T3 content than the normal human thyroid output ratio of approximately 14:1. This relative T3 excess means NDT often produces higher peak T3 levels and lower T4 levels compared to synthetic T4 monotherapy. While the ATA and most endocrine societies recommend synthetic levothyroxine as first-line therapy, a subset of patients — particularly those with DIO2 polymorphisms affecting T4-to-T3 conversion — report improved well-being, energy, and cognitive function on NDT compared to synthetic T4 alone. A 2013 RCT by Hoang et al. found that 48.6% of patients preferred NDT over levothyroxine, with NDT associated with more weight loss. NDT has faced supply issues and quality concerns, with several recalls for potency variability.
Indications
- FDA-approved: Hypothyroidism
- FDA-approved: Myxedema
- Off-label: Patient preference over synthetic T4 (better symptom control in subset)
- Off-label: DIO2 polymorphism (impaired T4-to-T3 conversion)
Mechanism of Action
NDT provides T4, T3, T2, T1, and calcitonin in ratios derived from porcine thyroid gland, mimicking natural thyroid output more closely than synthetic T4 alone
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Desiccated Thyroid (Armour) | 30 mg (0.5 grain) | Once daily | Starting dose; contains ~19 mcg T4 + 4.5 mcg T3 |
| Desiccated Thyroid | 60 mg (1 grain) | Once daily | Contains ~38 mcg T4 + 9 mcg T3; roughly equivalent to 100 mcg levothyroxine |
| Desiccated Thyroid | 90-120 mg (1.5-2 grains) | Once daily or divided | Higher replacement doses; consider dividing for T3 stability |
Evidence Grade
GRADE B
Safety & Contraindications
- Higher T3 content may cause supraphysiologic T3 peaks — cardiac risk in susceptible patients
- Batch-to-batch potency variation — more variable than synthetic levothyroxine
- Product recalls for subpotency and superpotency have occurred
- Porcine-derived — not suitable for patients with pork allergies or religious dietary restrictions
- TSH may be suppressed due to T3 content even at appropriate doses
- Not recommended in thyroid cancer suppression therapy by most guidelines