What is the evidence on natural desiccated thyroid?
Written and medically reviewed by Zahraa Sater, M.D., M.P.H.
Reviewed August 12, 2026 · Next review due August 12, 2028
Short answer
Desiccated thyroid extract is pig thyroid containing both T4 and T3. In the one substantial randomised crossover trial, symptoms and psychometric scores were no better than levothyroxine, although 49 percent of participants preferred it. The American Thyroid Association does not recommend it as first-line therapy, and these products were never approved by the FDA.
Get urgent care if: you take desiccated thyroid, liothyronine or any thyroid hormone and develop signs of hormone excess.
- A fast or irregular heartbeat, or a fluttering sensation in the chest that does not settle
- Chest pain or breathlessness at rest
- Fever with agitation or confusion in someone with known thyroid hormone excess
Desiccated thyroid extract is dried porcine thyroid gland, sold under names including Armour Thyroid and NP Thyroid. It contains both T4 and T3, at a T3 to T4 ratio much higher than a human thyroid produces. It is widely used and widely requested, and the honest summary is that the trial evidence shows equivalence on measured outcomes with a preference signal that has never been explained.
What the head to head trial showed
Hoang and colleagues published a randomised, double-blind crossover study of 70 patients with hypothyroidism, treated with one preparation for 12 weeks then switched to the other for a further period. Both treatments normalised thyroid function tests. There was no difference in psychometric testing or in any symptom score. Desiccated thyroid extract was associated with slightly more weight loss. On preference, 49 percent preferred desiccated extract, 19 percent preferred levothyroxine and 23 percent had no preference. That preference finding is real and should not be dismissed, but preference in an unblinded-by-effect crossover is a weaker endpoint than symptom scores.
What the guidelines say
The American Thyroid Association 2014 guideline recommends levothyroxine as the preparation of choice and found no consistently strong evidence for the superiority of thyroid extracts. The joint American, British and European Thyroid Association consensus on combination therapy describes desiccated thyroid extract as understudied and containing supraphysiological T3 to T4 ratios. Neither document bans it. Both decline to recommend it as first-line.
The practical problems with these products
Desiccated thyroid products predate the modern approval system and were never approved by the FDA, so they are not subject to the same potency and bioequivalence requirements as levothyroxine. Content can vary between batches, and supply has been interrupted by recalls. The high T3 fraction produces a post-dose T3 peak that suppresses TSH, which makes monitoring harder and raises the same arrhythmia and bone concerns that apply to liothyronine.
| Levothyroxine | Desiccated thyroid extract | |
|---|---|---|
| Contents | T4 only, synthetic | T4 and T3 from porcine thyroid |
| FDA approved | Yes | No |
| Guideline position | Preparation of choice | Not recommended first-line |
| Randomised evidence | Extensive | One crossover trial of 70 patients |
| Monitoring | TSH | TSH plus pulse and rhythm; TSH often suppressed |
If you are already taking desiccated thyroid and doing well, that is worth discussing rather than reversing on principle. If you are considering starting it, ask what specific problem it is meant to solve, and ask for a documented trial period with the same endpoints you would apply to any other change.
The clinical detail
Desiccated thyroid extract is standardised by grain: one grain, about 60 to 65 mg, supplies approximately 38 mcg of T4 and 9 mcg of T3, giving a T4 to T3 ratio near 4:1. Human thyroid secretion is closer to 14:1, which is why the T3 load is described as supraphysiological.
Expect a suppressed or low TSH with normal or low free T4 on adequate doses, particularly if blood is drawn within four hours of the dose. Draw thyroid function tests before the morning dose. In patients over 65, postmenopausal women and anyone with cardiac disease, monitor pulse and rhythm and consider bone densitometry, applying the same safeguards the joint thyroid association consensus specifies for liothyronine. Avoid in pregnancy, where the 2026 American Thyroid Association guideline advises against T3-containing therapy.
Written and medically reviewed by Zahraa Sater, M.D., M.P.H.
Reviewed August 12, 2026 · Next review due August 12, 2028
Sources
- Desiccated thyroid extract compared with levothyroxine in the treatment of hypothyroidism (patient summary of Hoang et al, J Clin Endocrinol Metab 2013). American Thyroid Association, Clinical Thyroidology for the Public
- Guidelines for the Treatment of Hypothyroidism. American Thyroid Association. PMID 25266247
- Evidence-Based Use of Levothyroxine/Liothyronine Combinations in Treating Hypothyroidism: A Consensus Document. American, British and European Thyroid Associations. PMID 33276704
- American Thyroid Association 2026 Guidelines for Thyroid Disease in Preconception, Pregnancy, and Postpartum. American Thyroid Association. PMID 42219800
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