Thyroid

What it is

Desiccated thyroid is a prescription tablet made from dried pig thyroid glands, standardised to contain levothyroxine (T4) and liothyronine (T3). It is an older alternative to synthetic levothyroxine. In the US it is sold as an unapproved drug: DailyMed states it has not been found by FDA to be safe and effective and its labeling has not been approved by FDA.

What the research says

It replaces thyroid hormone in people with an underactive thyroid. The one randomised crossover trial against levothyroxine found no difference in symptoms or thinking tests, a 3 lb weight loss, and that about half of patients preferred it. In mild (subclinical) hypothyroidism, trials of thyroid hormone (levothyroxine) found no improvement in quality of life or tiredness. Too much thyroid hormone in older adults is linked to fractures, and the label carries a boxed warning against using it for weight loss.

Evidence grade: Limited evidence.

How it works

Drug class: Thyroid hormone replacement (animal-derived T4 plus T3)

Desiccated thyroid is dried, powdered pig thyroid gland. It supplies both thyroid hormones, thyroxine (T4) and liothyronine (T3), which set the body's metabolic rate and raise oxygen use by most tissues. In replacement therapy it stands in for hormone the person's own thyroid no longer makes. (Source 1)

Boxed warning

Drugs with thyroid hormone activity, alone or together with other therapeutic agents, have been used for the treatment of obesity. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.

(Source 2)

What it is used for

• Thyroid hormone replacement for overt hypothyroidism is standard care. For desiccated thyroid specifically, the key trial is one 70-person crossover against levothyroxine: no difference in symptoms or cognition, modest weight loss, and 48.6% preferred it. The product itself is marketed as an unapproved drug in the US, so 'approved' here means it is the use the label describes. Evidence: limited. (Source 3)
• A meta-analysis of 21 randomised trials (2,192 adults) and the TRUST trial in people over 65 found thyroid hormone (levothyroxine) normalised TSH but did not improve quality of life, symptoms or tiredness. These trials used levothyroxine, not desiccated thyroid. Evidence: not-supported. (Source 4)
• The label's boxed warning states replacement doses do not cause weight loss in people with normal thyroid function and larger doses can be life-threatening. Evidence: not-supported. (Source 2)
• Listed in the label; we did not research outcome evidence for desiccated thyroid in this use. Evidence: unknown. (Source 2)

Interactions

• Calcium carbonate (clinical trial): Taking calcium carbonate with thyroxine lowered T4 levels and raised TSH, meaning less hormone was absorbed. Levels recovered after calcium was stopped. Studied with levothyroxine, the T4 component of desiccated thyroid. (Source 5)
• Iron (ferrous sulfate) (clinical trial): Taking iron at the same time as thyroxine raised TSH from 1.6 to 5.4 mU/L over 12 weeks and nine of 14 patients had more hypothyroid symptoms. Studied with levothyroxine. (Source 6)
• High-fibre diet, sucralfate, aluminium antacids (case reports): The commentary on the calcium study notes that high-fibre diets, and drugs such as sucralfate, bile acid sequestrants and aluminium hydroxide, have also been shown to interfere with thyroxine absorption. (Source 7)
• Warfarin and other oral anticoagulants (vitamin K antagonists) (label): Thyroid hormone speeds breakdown of vitamin K-dependent clotting factors, so it can strengthen the effect of warfarin. (Source 8)
• Cholestyramine and colestipol (label): These bind thyroid hormone in the gut and reduce absorption. (Source 8)
• Insulin and oral diabetes drugs (label): Starting thyroid replacement can raise the dose of diabetes medicine needed. (Source 8)

Stopping it

• A 2021 meta-analysis (17 observational studies, 1,103 patients, median 5 years) found about a third of people stayed euthyroid after stopping thyroid hormone, far fewer after overt than subclinical hypothyroidism; most restarted treatment. (Source 9)
• Stopping succeeded far less often in people who had overt hypothyroidism. (Source 9)
• Only three of the studies described how the dose was reduced, and the approaches differed (from 2 weeks to several months), so the best way to taper is not known. (Source 10)

What goes wrong

Among adults 70 and older, current levothyroxine use was associated with higher fracture risk, rising with dose. This is an association, not proof of cause. (Source 11)

• Case-control study, Low certainty.
• Size: 213,511 levothyroxine users; 22,236 fractures.
• Who: Adults aged 70 or older in Ontario.
• How long: Mean 3.8 years follow-up.
• Result: Adjusted OR 1.88 for current vs remote use; high vs low cumulative dose 3.45-fold.
• Funding: not stated on the page we read.

Among adults aged 70 or more, current levothyroxine treatment was associated with a significantly increased risk of fracture, with a strong dose-response relation.

Using thyroid hormone for weight loss in people with normal thyroid function is ineffective at replacement doses and can be life-threatening at higher doses. (Source 2)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: People with normal thyroid function.
• How long: not applicable.
• Result: Regulatory boxed warning.
• Funding: manufacturer label.

In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction.

Many older adults taking thyroid hormone end up over-replaced, which carries risks to heart rhythm and bone (as reported from a 2021 meta-analysis). (Source 10)

• Systematic review, Low certainty.
• Size: 17 studies, 1,103 patients (discontinuation meta-analysis)
• Who: Patients treated with thyroid hormone.
• How long: Median 5 years follow-up.
• Result: As many as 50% of patients over 65 develop iatrogenic hyperthyroidism (authors' statement, as reported)
• Funding: not stated.

The authors say there is evidence indicating that as many as 50% of patients older than 65 who take thyroid hormones develop iatrogenic hyperthyroidism

What the evidence supports

People lost a small amount of weight while taking desiccated thyroid compared with levothyroxine. (Source 3)

• Randomized trial, Low certainty.
• Size: 70 patients.
• Who: Adults with primary hypothyroidism.
• How long: 16 weeks per arm.
• Result: 3 lb lower weight on DTE (172.9 vs 175.7 lb, P < .001)
• Funding: not stated in the abstract.

Patients lost 3 lb on DTE treatment (172.9 ± 36.4 lb vs 175.7 ± 37.7 lb, P < .001).

What the evidence does not support

In adults with mild (subclinical) hypothyroidism, thyroid hormone therapy normalised TSH but did not improve quality of life or thyroid symptoms. (Source 4)

• Meta-analysis, Moderate certainty.
• Size: 21 RCTs, 2,192 adults.
• Who: Nonpregnant adults with subclinical hypothyroidism (levothyroxine trials)
• How long: 3-18 months.
• Result: Quality of life SMD −0.11 (95% CI −0.25 to 0.03); thyroid symptoms SMD 0.01 (−0.12 to 0.14); GRADE moderate to high.
• Funding: academic (not industry) per author list; not stated in abstract.

Among nonpregnant adults with subclinical hypothyroidism, the use of thyroid hormone therapy was not associated with improvements in general quality of life or thyroid-related symptoms.

In adults 65 and over with mild hypothyroidism, levothyroxine did not improve hypothyroid symptoms or tiredness compared with placebo. (Source 12)

• Randomized trial, High certainty.
• Size: 737 adults.
• Who: Adults aged 65 or older with persisting subclinical hypothyroidism.
• How long: 1 year.
• Result: Hypothyroid Symptoms score between-group difference 0.0 (95% CI −2.0 to 2.1); Tiredness 0.4 (−2.1 to 2.9)
• Funding: European Union FP7 and others (independent)

Levothyroxine provided no apparent benefits in older persons with subclinical hypothyroidism.

Where the evidence is mixed

Compared with levothyroxine in a crossover trial, desiccated thyroid gave no difference in symptoms or thinking tests, but nearly half of patients preferred it. (Source 3)

• Randomized trial, Low certainty.
• Size: 70 patients.
• Who: Adults 18-65 with primary hypothyroidism stable on levothyroxine.
• How long: 16 weeks on each treatment.
• Result: No differences in symptoms or neurocognitive measures; 48.6% preferred DTE, 18.6% preferred L-T4, 32.9% no preference.
• Funding: not stated in the abstract (single military tertiary centre)

There were no differences in symptoms and neurocognitive measurements between the 2 therapies.

Where the research disagrees

Whether desiccated thyroid is better than levothyroxine

• Hoang et al., JCEM 2013, rct (crossover, n=70): DTE therapy did not result in a significant improvement in quality of life; however, DTE caused modest weight loss and nearly half (48.6%) of the study patients expressed preference for DTE over L-T4. (Source 3)

How much

• Reference intake: Dosing is set by the prescriber and adjusted to blood tests. The Armour Thyroid label (updated March 2024) states the usual starting dose is 30 mg with 15 mg increments, a lower start where heart disease is suspected, and that most patients require 60 to 120 mg/day. These are the label's positions. (Source 13)
• Upper limit: The label gives no fixed maximum; it states that failure to respond to 180 mg suggests poor adherence or malabsorption. This is the label's position. (Source 13)
• Studied: The TRUST trial (levothyroxine) started at 50 μg daily, or 25 μg for low body weight or heart disease, and reached a median dose of 50 μg. (Source 12)
• Studied: The Hoang crossover trial gave desiccated thyroid or levothyroxine for 16 weeks each. (Source 3)

A common belief, and what the research shows

The belief: Thyroid pills help with weight loss.

What the research shows: The label's boxed warning says "In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction." In the crossover trial of hypothyroid patients, the difference versus levothyroxine was 3 lb.

Questions and answers

What is it?

A prescription tablet made from dried pig thyroid glands that contains the thyroid hormones T4 and T3. (Source 14)

What does it do in the body?

It supplies thyroid hormone, which raises the body's metabolic rate and oxygen use, replacing hormone an underactive thyroid no longer makes. (Source 1)

Is it good or bad for you?

For true hypothyroidism it replaces missing hormone; one trial found it neither better nor worse than levothyroxine on symptoms. In mild (subclinical) hypothyroidism trials of thyroid hormone showed no benefit, and too much hormone in older adults is linked to fractures. (Source 3)

How do you get more of it?

Does not apply as a food or supplement question. Desiccated thyroid is prescription-only and the dose is set by the prescriber against blood tests. (Source 13)

If it is harmful, what reduces it?

Over-replacement is lowered by the prescriber adjusting the dose. Studies of stopping found about a third of people stay euthyroid, fewer if they had overt hypothyroidism. (Source 9)

Why might someone be low in it or missing it?

Does not apply to the drug itself. Absorption of thyroid hormone can be reduced by taking it with calcium, iron, high-fibre meals or bile-acid binders. (Source 6)

Which whole foods contain it or feed it?

No ordinary food supplies thyroid hormone in useful amounts. High-fibre diets can reduce absorption of thyroxine. (Source 7)

What happens if you do not have it?

When a person on replacement stops, many become hypothyroid again: after overt hypothyroidism only about 12% stayed euthyroid, and 87% restarted treatment. (Source 9)

How can you test for it?

Thyroid hormone treatment is monitored with a blood test for TSH (thyrotropin), and sometimes free T4. Trials used TSH to judge dose. (Source 12)

References

1. Manufacturer labeling (Allergan) posted on DailyMed; DailyMed lists it as an unapproved drug whose labeling has not been approved by FDA. Armour Thyroid (thyroid tablets, USP) - Prescribing Information (DailyMed, updated March 13, 2024), Clinical Pharmacology. 2024. Read the source
2. Manufacturer labeling (Allergan) posted on DailyMed; DailyMed lists it as an unapproved drug whose labeling has not been approved by FDA. Armour Thyroid (thyroid tablets, USP) - Prescribing Information (DailyMed, updated March 13, 2024), Boxed Warning. 2024. Read the source
3. Journal of Clinical Endocrinology and Metabolism. Desiccated thyroid extract compared with levothyroxine in the treatment of hypothyroidism: A randomized, double-blind, crossover study. 2013. DOI 10.1210/jc.2012-4107. Read the source
4. JAMA. Association of Thyroid Hormone Therapy With Quality of Life and Thyroid-Related Symptoms in Patients With Subclinical Hypothyroidism: A Systematic Review and Meta-analysis. 2018. DOI 10.1001/jama.2018.13770. Read the source
5. Clinician.com (Relias Media), Therapeutics and Drugs Briefs, August 1, 2000; comment by Ralph R. Hall, MD, FACP. Treating Hypothyroidism Isn't Always as Simple as it Seems (item in 'Therapeutics and Drugs Briefs'), summarising Singh N et al., Effect of calcium carbonate on the absorption of levothyroxine, JAMA 2000;283:2822-2825 (PMID 10838651), conclusion sentence. 2000. Read the source
6. Annals of Internal Medicine. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism (Campbell NR et al., Ann Intern Med 1992;117(12):1010-3), abstract conclusion. 1992. PMID 1443969. Read the source
7. Clinician.com (Relias Media), Therapeutics and Drugs Briefs, August 1, 2000; comment by Ralph R. Hall, MD, FACP. Treating Hypothyroidism Isn't Always as Simple as it Seems (item in 'Therapeutics and Drugs Briefs'), summarising Singh N et al., Effect of calcium carbonate on the absorption of levothyroxine, JAMA 2000;283:2822-2825 (PMID 10838651), other interfering drugs and fibre. 2000. Read the source
8. Manufacturer labeling (Allergan) posted on DailyMed; DailyMed lists it as an unapproved drug whose labeling has not been approved by FDA. Armour Thyroid (thyroid tablets, USP) - Prescribing Information (DailyMed, updated March 13, 2024), Precautions: Drug Interactions. 2024. Read the source
9. The Hospitalist (MDedge), news article by Nancy A. Melville, February 2021. A third discontinuing levothyroxine have normal thyroid levels (news report of Burgos N et al., Thyroid 2021, meta-analysis), results. 2021. Read the source
10. The Hospitalist (MDedge), news article by Nancy A. Melville, February 2021. A third discontinuing levothyroxine have normal thyroid levels (news report of Burgos N et al., Thyroid 2021, meta-analysis), tapering and reasons for discontinuing. 2021. Read the source
11. Global Family Doctor (WONCA) Journal Watch. Levothyroxine dose and risk of fractures in older adults: nested case-control study (Turner MR et al., BMJ 2011;342:d2238), journal-watch summary. 2011. Read the source
12. New England Journal of Medicine. Thyroid hormone therapy for older adults with subclinical hypothyroidism (TRUST). 2017. DOI 10.1056/NEJMoa1603825. Read the source
13. Manufacturer labeling (Allergan) posted on DailyMed; DailyMed lists it as an unapproved drug whose labeling has not been approved by FDA. Armour Thyroid (thyroid tablets, USP) - Prescribing Information (DailyMed, updated March 13, 2024), Dosage and Administration: Hypothyroidism. 2024. Read the source
14. Manufacturer labeling (Allergan) posted on DailyMed; DailyMed lists it as an unapproved drug whose labeling has not been approved by FDA. Armour Thyroid (thyroid tablets, USP) - Prescribing Information (DailyMed, updated March 13, 2024), Description. 2024. Read the source