Levothyroxine, a synthetic T4, is the standard treatment for hypothyroidism. Some patients still feel unwell on it, and two alternatives are often offered: adding liothyronine (synthetic T3), or desiccated thyroid, a product made from animal thyroid glands. The 2014 American Thyroid Association guideline concluded that levothyroxine should remain the standard of care, and found no consistently strong evidence that the alternatives improve health outcomes. The trials below are small and measured different things, so read them as open questions, not as a verdict.
The standard: levothyroxine
The American Thyroid Association recommends levothyroxine as the standard treatment for hypothyroidism. Its authors reviewed the alternatives and found no consistently strong evidence that thyroid extract, or levothyroxine plus liothyronine, is superior to levothyroxine alone for health outcomes (Jonklaas 2014).
Adding T3: the 2021 crossover trial
In a randomized, double-blind crossover trial, 75 adults with hypothyroidism took levothyroxine alone, levothyroxine plus liothyronine, or desiccated thyroid, each for 22 weeks. TSH stayed in the reference range in all three arms. Primary and secondary outcomes did not differ, except a small rise in heart rate on desiccated thyroid (Shakir 2021).
The most symptomatic patients on levothyroxine alone preferred treatment with T3 and scored better on symptom, mood and memory measures on it. That subgroup was the most symptomatic third of the trial, so the finding is a reason to talk, not a rule.
Desiccated thyroid: a 16-week crossover trial
In a randomized, double-blind crossover trial of 70 adults with primary hypothyroidism, each person took desiccated thyroid extract, the active ingredient of products such as Armour Thyroid, and levothyroxine for 16 weeks, then switched. Symptom and neurocognitive measures did not differ between the two (Hoang 2013).
Participants lost about 3 lb on desiccated thyroid. The authors describe that loss as modest, and it is not a reason to take thyroid hormone. After the trial, 48.6% preferred desiccated thyroid, 18.6% preferred levothyroxine and 32.9% had no preference.
Why we start with levothyroxine
In our view, levothyroxine has a consistent strength, a known dose and a long record of use. The trials that compare the alternatives are small and short, so a patient who prefers another product is part of the conversation, and we discuss the trade-offs before any change.
Who may still be considered
Patients who still have symptoms after their TSH is well controlled on levothyroxine may be considered for a trial of T3 or desiccated thyroid with their physician. The trials do not show that either improves outcomes for everyone, so we recheck symptoms and labs during any change.
What this does not say
- The trials are small and short: 70 and 75 adults, followed for 16 and 22 weeks.
- Preference is not the same as a better treatment. Symptom scores did not differ overall in either trial.
- Thyroid hormone is not a weight-loss treatment. The small weight change in the desiccated thyroid trial does not make it one, and we do not prescribe it for that.
- Desiccated thyroid products are not FDA-approved, and their hormone content is less standardized than levothyroxine.
- The results apply to the products and doses tested, not to every compounded or differently sourced product.
How we use this
Our physicians start with levothyroxine. When someone asks about T3 or desiccated thyroid, we explain what the trials tested and what they did not show, then decide with the patient based on symptoms and labs.
Explore weight loss treatmentsSources
- 1.Guidelines for the Treatment of Hypothyroidism: prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement Jonklaas J et al., Thyroid, 2014
- 2.Desiccated thyroid extract compared with levothyroxine in the treatment of hypothyroidism: a randomized, double-blind, crossover study Hoang TD et al., J Clin Endocrinol Metab, 2013
- 3.Comparative Effectiveness of Levothyroxine, Desiccated Thyroid Extract, and Levothyroxine+Liothyronine in Hypothyroidism Shakir MKM et al., J Clin Endocrinol Metab, 2021