Desiccated Thyroid
See our Evidence Standards for how we grade the research below.
What It Is
Desiccated thyroid extract (DTE) is derived from dried, powdered pig thyroid gland, and unlike synthetic levothyroxine (T4-only), it contains both T4 and T3, the two thyroid hormones the human thyroid gland itself produces, in a fixed ratio set by pig physiology rather than adjustable to an individual patient. The standard of care for hypothyroidism is levothyroxine monotherapy, on the reasoning that the body converts T4 into active T3 as needed via deiodinase enzymes. DTE and other T3-containing regimens are studied because a meaningful subset of patients report persistent symptoms on levothyroxine alone despite a normal TSH, and T3 supplementation is one proposed explanation and remedy.
The Evidence
Hoang TD, Olsen CH, Mai VQ, Clyde PW, Shakir MKM. "Desiccated Thyroid Extract Compared With Levothyroxine in the Treatment of Hypothyroidism: A Randomized, Double-Blind, Crossover Study." Journal of Clinical Endocrinology & Metabolism. 2013 May;98(5):1982-1990. PMID: 23539727. Randomized, double-blind, crossover trial, 70 patients (18-65 years old) with primary hypothyroidism already stable on levothyroxine, switched to DTE or continued levothyroxine for 12 weeks, then crossed over to the other treatment for 16 weeks, blinded throughout. There were no significant differences in symptoms or neurocognitive test performance between the two treatments. Despite the absence of an objective difference, patients showed a real preference: 49% preferred DTE, 19% preferred levothyroxine, and 23% had no preference. DTE was also associated with modest weight loss relative to levothyroxine.
Shakir MKM, Brooks DI, McAninch EA, Fonseca TL, Mai VQ, Bianco AC, Hoang TD. "Comparative Effectiveness of Levothyroxine, Desiccated Thyroid Extract, and Levothyroxine+Liothyronine in Hypothyroidism." Journal of Clinical Endocrinology & Metabolism. 2021 Nov;106(11):e4400-e4413. Randomized, double-blind, crossover trial, 75 patients, three treatment arms (levothyroxine alone, levothyroxine plus liothyronine/T3, and DTE), 22 weeks per arm. As a whole group, there were no significant differences across arms in symptom scores, quality of life, memory testing, or depression scores, and TSH stayed within range on all three regimens; DTE was associated with a minor increase in heart rate. The key finding was in a pre-specified subgroup: the third of patients who were most symptomatic while on levothyroxine alone (by mood, cognitive, and quality-of-life scores) improved significantly after switching to a T3-containing regimen, either DTE or levothyroxine plus liothyronine, and this subgroup also preferred the T3-containing option. A genetic variant in the deiodinase enzyme (DIO2) that some have proposed explains who responds to T3 did not predict which patients improved.
What's Reported in Practice
Patients who feel persistently unwell on levothyroxine alone, despite normal labs, commonly report meaningful improvement in energy, mental clarity, and overall wellbeing after switching to DTE or a T3-containing regimen. The 2021 trial above gives this real support: it isn't just a general perception, there's an identifiable subgroup of the most symptomatic levothyroxine patients who measurably improve on T3-containing therapy. We think this is a genuine, trial-supported pattern, not just an anecdote, though it applies to a specific subgroup rather than to everyone on levothyroxine.
What the Research Doesn't Yet Show
This is where we're most eager to see more research investment, not a mark against DTE. Averaged across whole study populations, DTE and T3-containing regimens haven't shown a clear advantage over levothyroxine alone, which is why levothyroxine remains the default starting point. What both trials above do show is a real, specific subgroup, roughly a third of patients in the 2021 trial, who improve measurably on T3-containing therapy after not doing well on levothyroxine alone. What isn't yet established is how to reliably identify that subgroup in advance: the DIO2 genetic variant some have proposed as a predictor didn't pan out in the 2021 trial, so right now the only reliable way to find out if someone is in that responsive subgroup is a clinical trial of therapy itself, guided by symptoms rather than a lab test or genetic marker. Neither trial was large enough or long enough to speak to long-term cardiovascular or bone safety of T3-containing regimens, which remains an open question worth a larger, longer trial.
Available as an FDA-approved prescription product and via compounded formulations; specific product and dose are individualized based on your history, labs, and symptoms, and discussed at your visit.
Next Step
This page covers mechanism and evidence. Dosing, monitoring, and whether this is appropriate for you are individual clinical decisions made with your provider.
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