medicationPrescription only (US)Liothyronine (synthetic T3) is FDA-approved for hypothyroidism; its use in combination with levothyroxine remains an area of active clinical trial investigation rather than a settled first-line recommendation
LiothyronineBenefits, Dosage & Interactions
Also known as: T3, Cytomel
Liothyronine, also known by its chemical abbreviation T3, is a synthetic form of the naturally occurring thyroid hormone triiodothyronine. It is available as a prescription medication and is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones.
How much Liothyronine do people take?
Added to levothyroxine as a fixed T4:T3 combination in the LEVOLIO study (totally thyroidectomized subjects); the Azizi et al. protocol describes a slow-release liothyronine formulation combined with levothyroxine, with the completed comparative-effectiveness trial titrating levothyroxine+liothyronine combinations to a target TSH. Route reported: Oral tablet. Frequency reported: Once or twice daily depending on the formulation and protocol cited. These are amounts documented in the cited studies and labels for Liothyronine — they are reported for reference, not a recommendation. Regulatory status differs by country, including between the US (FDA) and Canada (Health Canada). Confirm any amount with a licensed clinician before you take it.
See the full reported protocol and its sourcesResearched by DoseRoutine Research TeamReviewed for accuracy by Nicholas Alexander, RSE, SO, PMPLast updated Educational reference only — not medical advice. Always confirm dosing and safety decisions with a licensed clinician.
Evidence: Strong — 2 human randomized trials and regulatory approval on file.
Evidence strengthStrong · 4/4
PreclinicalStrong human evidence
2 human randomized trials and regulatory approval on file.
Is liothyronine the same hormone as levothyroxine?
No. Liothyronine supplies T3, while levothyroxine supplies T4. Their milligram or microgram amounts are not interchangeable, and switching requires clinical interpretation of symptoms and thyroid tests.
Source: MedlinePlus: Liothyronine
Browse compound evidence cardsPlasma half-life
~25 h
Typical timing
in the morning
Food rule
on an empty stomach
Default unit
mcg
What published protocols report
Ranges documented in the literature, shown for reference. DoseRoutine does not recommend an amount — your prescriber or the product label sets the dose.
- Reported amounts
- Added to levothyroxine as a fixed T4:T3 combination in the LEVOLIO study (totally thyroidectomized subjects); the Azizi et al. protocol describes a slow-release liothyronine formulation combined with levothyroxine, with the completed comparative-effectiveness trial titrating levothyroxine+liothyronine combinations to a target TSH[1][2][3]
Reported for Liothyronine in the cited sources. Published ranges are not dosing advice.
References & evidence
Documents the Liothyronine entry is written from. Each number matches an inline marker above.
- [1]Randomized double-blind placebo-controlled trial on levothyroxine and liothyronine combination therapy in totally thyroidectomized subjects: the LEVOLIO studyBrigante G, Santi D, Boselli G, Margiotta G, Corleto R, Monzani ML, Craparo A, Locaso M, Sperduti S, Roy N, Casarini L, Trenti T, Tagliavini S, De Santis MC, Roli L, Rochira V, Simoni M · European Journal of Endocrinology · 2024 · Peer-reviewed · PMID 38124252
- [2]Comparative Effectiveness of Levothyroxine, Desiccated Thyroid Extract, and Levothyroxine+Liothyronine in HypothyroidismShakir MKM, Brooks DI, McAninch EA, Fonseca TL, Mai VQ, Bianco AC, Hoang TD · The Journal of Clinical Endocrinology & Metabolism · 2021 · Peer-reviewed · PMID 34185829
- [3]Treatment of hypothyroidism with levothyroxine plus slow-release liothyronine: a study protocol for a randomized controlled double-blinded clinical trialAzizi F, Amouzegar A, Abdi H, Tohidi M, Masoumi S, Khalili D, Mehrabi Y, Zadehvakili A, Hedayati M, Momenan AA, Mehran L · Trials · 2025 · Peer-reviewed · PMID 40598574
References & Evidence
Sources on this page that document Liothyronine dosing, timing and safety.
- [1]National Center for Biotechnology Information View source
- [2]U.S. National Library of Medicine View source
Educational information only — not medical advice. Dose ranges vary by person, indication and prescriber.
What is Liothyronine?Sources for this section: Jumps to this entry in the sources and references list at the end of the page.
Liothyronine, also known by its chemical abbreviation T3, is a synthetic form of the naturally occurring thyroid hormone triiodothyronine. It is available as a prescription medication and is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones. Unlike levothyroxine (T4), which is a prohormone that needs to be converted into T3 by the body, liothyronine is the active form of the hormone, leading to a faster onset of action and elimination.
Historically, liothyronine has been used alone or in combination with levothyroxine for thyroid hormone replacement therapy. It is also used in the diagnosis of hyperthyroidism (an overactive thyroid gland) and as an adjunct to surgery and radioiodine therapy in the management of thyroid cancer. While not directly indicated for weight loss, its role in metabolism has led to some off-label discussions regarding its effects on body weight, particularly in complex thyroid cases. The medication is typically taken orally in tablet form.
What does the research say about Liothyronine?
Tap a section to expand.
Liothyronine (T3) exerts its physiological effects by binding to specific thyroid hormone receptors located within the nucleus of cells throughout the body. Once bound, the T3-receptor complex interacts with DNA, modulating gene expression. This regulation of gene expression influences a wide array of metabolic processes, including energy production, protein synthesis, fat metabolism, and carbohydrate utilization. By increasing the synthesis of various enzymes and structural proteins, T3 plays a crucial role in maintaining normal metabolic rate, body temperature, cardiovascular function, and central nervous system development and activity. Because T3 is the most metabolically active form of thyroid hormone, its administration directly provides the active hormone required for cellular function, bypassing the need for peripheral conversion from T4. This direct action contributes to liothyronine's rapid onset and offset of effects compared to levothyroxine (T4). (Source: PubChem, DrugBank)
Source for this section: Sources for How does Liothyronine work?: Jumps to this entry in the sources and references list at the end of the page.
The primary benefit of liothyronine is its effectiveness in treating hypothyroidism, a condition characterized by insufficient thyroid hormone production. For individuals with hypothyroidism, liothyronine replacement therapy helps to restore normal metabolic function, alleviating symptoms such as fatigue, weight gain, cold intolerance, constipation, dry skin, and depression. Its direct action as the active T3 hormone may be particularly beneficial for patients who have impaired conversion of T4 to T3, though this is a subject of ongoing clinical debate and research. (Source: NIH ODS, DrugBank)
In specific diagnostic contexts, liothyronine can be used in a T3 suppression test to help diagnose hyperthyroidism by evaluating the thyroid gland's responsiveness to negative feedback. It also plays a role as an adjunct therapy in the management of thyroid cancer, particularly during preparation for radioactive iodine scanning and treatment, by elevating TSH levels (thyroid-stimulating hormone) which helps in the uptake of iodine by remaining thyroid cancer cells after surgery. (Source: FDA label)
Clinical evidence for liothyronine's efficacy in hypothyroidism primarily stems from its long-standing use and biological plausibility as a direct thyroid hormone replacement. While levothyroxine (T4) is generally considered the standard first-line treatment, some studies and clinical practice suggest that a subset of patients may benefit from combination therapy with both levothyronine and liothyronine. A Cochrane review on combination T4 and T3 hormone replacement therapy found that some patients reported improvements in mood and quality of life measures with combination therapy compared to T4 monotherapy, although these findings were not consistently replicated across all studies and effects on body weight or thyroid-related symptoms were often not significantly different. (Source: Cochrane)
Research continues to explore optimal dosing strategies and identifying specific patient populations who may respond better to T3-containing regimens. The FDA label provides detailed information on its approved indications and safety profile, reflecting the extensive clinical data supporting its use in thyroid disorders. (Source: FDA label)
Side effects of liothyronine are typically associated with excessive dosage, mimicking symptoms of hyperthyroidism. These can include:
* Palpitations, increased heart rate (tachycardia), and other cardiac arrhythmias
* Chest pain (angina)
* Nervousness, tremors, irritability
* Insomnia
* Increased sweating
* Heat intolerance
* Weight loss (often unintended and rapid)
* Diarrhea
* Muscle weakness and cramps
* Headache
* Changes in menstrual cycle
Symptoms of over-treatment should be reported to a clinician immediately. Acute massive overdosage can be life-threatening, especially in patients with pre-existing heart conditions. This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.
Source for this section: Sources for What are the side effects of Liothyronine?: Jumps to this entry in the sources and references list at the end of the page.
Liothyronine should be used with caution in patients with known cardiovascular disease, including angina, coronary artery disease, and arrhythmias, as thyroid hormones can increase cardiac work and oxygen demand. In older patients or those with a history of heart disease, dosage initiation should be lower and titration gradual. Patients with adrenal insufficiency should have this condition treated before initiating liothyronine, as thyroid hormone replacement can precipitate an acute adrenal crisis. Thyroid hormones are not indicated for the treatment of obesity or for weight reduction in euthyroid (normal thyroid function) patients; doses within the physiological range are ineffective for weight reduction, and larger doses may produce serious or even life-threatening toxicity, particularly when given in conjunction with other anorectic drugs. Extreme caution should be exercised in patients with diabetes mellitus or diabetes insipidus, as thyroid hormone therapy may alter requirements for insulin or oral antidiabetic agents.
Regular monitoring of thyroid function tests (TSH, free T3) is essential to ensure appropriate dosing and prevent over-treatment or under-treatment. This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.
Source for this section: Sources for Who should avoid Liothyronine?: Jumps to this entry in the sources and references list at the end of the page.
Liothyronine is contraindicated in individuals with uncorrected adrenal insufficiency, as thyroid hormone administration can worsen this condition. It is also contraindicated in cases of diagnosed but untreated thyrotoxicosis (hyperthyroidism from any cause) due to the risk of exacerbating symptoms and potential cardiac complications. Patients with hypersensitivity to liothyronine or any component of the formulation should also avoid its use. Use in conjunction with drugs for weight loss, especially at supraphysiological doses, is contraindicated due to the risk of severe and potentially fatal adverse effects. This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.
Source for this section: Sources for When should Liothyronine not be taken?: Jumps to this entry in the sources and references list at the end of the page.
Several medications can interact with liothyronine, potentially altering its effectiveness or increasing the risk of adverse effects:
* **Anticoagulants (e.g., warfarin):** Thyroid hormones can increase the anticoagulant effect, potentially leading to an increased risk of bleeding. Close monitoring of INR and dose adjustment may be necessary.
* **Digitalis glycosides:** The effects of digitalis may be decreased in hypothyroid patients and enhanced by thyroid hormone replacement.
* **Antidiabetic agents (e.g., insulin, oral hypoglycemics):** Thyroid hormones can increase blood glucose levels, potentially requiring adjustments in antidiabetic medication dosages.
* **Cholestyramine and colestipol:** These bile acid sequestrants can bind to thyroid hormones in the gastrointestinal tract, reducing their absorption. Liothyronine should be taken several hours apart from these medications.
* **Estrogen-containing oral contraceptives and estrogen replacement therapy:** Estrogens can increase thyroid binding globulin (TBG), requiring an increased dose of liothyronine.
* **Tricyclic antidepressants (e.g., imipramine, amitriptyline):** Co-administration may increase the risk of cardiac arrhythmias and toxicity.
* **Beta-blockers (e.g., propranolol, metoprolol):** Effectiveness of beta-blockers may be altered.
* **Corticosteroids:** Thyroid hormones can increase the metabolic clearance of corticosteroids.
Always inform your healthcare provider about all medications, supplements, and herbal products you are taking to identify potential interactions. This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.
Source for this section: Sources for What should you not mix with Liothyronine?: Jumps to this entry in the sources and references list at the end of the page.
Liothyronine is typically taken once daily, usually in the morning. This timing helps to mimic the body's natural diurnal rhythm of thyroid hormone release and minimize potential sleep disturbances that could arise from taking it later in the day. It is often recommended to take liothyronine on an empty stomach, at least 30 minutes to an hour before food or other medications, to ensure optimal absorption. Consistency in timing and relation to meals is important for maintaining stable thyroid hormone levels. The specific dose and timing must be set by a licensed clinician.
Source for this section: Sources for When should you take Liothyronine?: Jumps to this entry in the sources and references list at the end of the page.
Put it into practice
Reading about Liothyronine is the first step — DoseRoutine helps you act on it. These free tools turn what you just learned into a routine.
What interacts with Liothyronine?
| Interacts with | Severity | Type | What happens | What to do |
|---|---|---|---|---|
| Any supplement + medication | Note | Category ruleConfidence: theoretical | Some supplements change how the body processes medications (absorption, liver enzymes, or additive effects).Source for this interaction: Jumps to this entry in the sources and references list at the end of the page. | Specific pairs are checked against a licensed drug database and shown with their own severity. Always confirm with your provider or pharmacist. |
| Any vitamin + medication | Note | Category ruleConfidence: theoretical | Certain vitamins interact with specific medications (e.g., vitamin K with blood thinners).Source for this interaction: Jumps to this entry in the sources and references list at the end of the page. | Specific pairs are checked against a licensed source; confirm with your provider. |
| Calcium | Caution | Compound pairConfidence: theoretical | Minerals chelate T3 and reduce absorption.Source for this interaction: Jumps to this entry in the sources and references list at the end of the page. | Separate liothyronine and mineral supplements by at least 4 hours.Suggested separation: 4 h |
| Iron (ferrous bisglycinate) | Caution | Compound pairConfidence: theoretical | Minerals chelate T3 and reduce absorption.Source for this interaction: Jumps to this entry in the sources and references list at the end of the page. | Separate liothyronine and mineral supplements by at least 4 hours.Suggested separation: 4 h |
| Magnesium Glycinate | Caution | Compound pairConfidence: theoretical | Minerals chelate T3 and reduce absorption.Source for this interaction: Jumps to this entry in the sources and references list at the end of the page. | Separate liothyronine and mineral supplements by at least 4 hours.Suggested separation: 4 h |
Frequently asked questions about Liothyronine
Levothyroxine (T4) is a prohormone that the body converts into the active hormone, T3. Liothyronine (T3) is the active form itself. T4 has a longer half-life, meaning it stays in the body longer, while T3 has a shorter half-life and a faster onset of action. Most thyroid replacement therapy uses T4, but some individuals may benefit from T3 or combination therapy.
While thyroid hormones influence metabolism, liothyronine is not approved or recommended for weight loss in individuals with normal thyroid function. Taking excessive doses to induce weight loss can lead to serious and potentially life-threatening side effects, especially cardiovascular complications. In hypothyroid patients, appropriate replacement therapy can help normalize weight if weight gain was a symptom of their underactive thyroid.
Due to its direct action as the active T3 hormone, the effects of liothyronine can be noticed relatively quickly, often within a few days to a week. However, the full therapeutic effect and stabilization of hormone levels may take several weeks, and dosage adjustments can continue based on clinical response and lab test results.
While generally no strict dietary restrictions exist, it's advisable to take liothyronine on an empty stomach to ensure consistent absorption. Products containing calcium, iron, or soy may interfere with absorption if taken at the same time. It's best to separate these by several hours.
Thyroid hormone requirements often increase during pregnancy. Maintaining euthyroidism is crucial for both maternal and fetal health. Liothyronine has been used in pregnancy under close medical supervision, though levothyroxine (T4) is generally preferred as it crosses the placenta less readily and maintains more stable levels. Any pregnant individual on liothyronine must have their thyroid function closely monitored and dosage adjusted by a clinician.
As a medication, Liothyronine can overlap with other supplements, prescription medicines, hormones and peptides. Because Liothyronine is usually taken in the morning, most avoidable conflicts come from what else lands in that same window. With a reported plasma half-life near 25 hours, separating doses can change the picture as much as removing one. Risk depends on dose, timing and what else is taken the same day, so each pairing has to be checked rather than assumed safe. The free checker at https://doseroutine.com/interaction-checker covers Liothyronine with no sign-up.
Liothyronine is typically taken in the morning. Published protocols usually have it taken on an empty stomach. The reported plasma half-life is about 25 hours, which is what drives how often it is redosed. Amounts for this medication vary by protocol, formulation and individual response, so follow the dose your clinician or the product label specifies.
Whether Liothyronine fits alongside testosterone replacement therapy depends on the protocol — dose, ester and ancillaries such as HCG or anastrozole — and on current bloodwork. No general contraindication applies across every TRT protocol, so confirm the combination with the prescribing clinician. See the free TRT interaction reference: https://doseroutine.com/trt-supplement-interactions
"Peptides" is not one category — healing peptides, GLP-1 agonists, growth-hormone secretagogues and melanocortins each behave differently next to Liothyronine. Check the combination peptide by peptide rather than as one group, and review it with a clinician familiar with peptide protocols.
With a plasma half-life near 25 hours, once-daily dosing is the usual pattern for Liothyronine. It is typically taken in the morning. Most protocols have it taken on an empty stomach. Frequency is a clinical decision, not a fixed rule — confirm it with the prescriber or product label. Comparison of apps that keep a schedule like this: https://doseroutine.com/best-dose-tracking-apps
With a plasma half-life near 25 hours, a single missed dose of Liothyronine usually has a smaller effect on overall exposure than an irregular pattern of missed doses does. Doubling up to "catch up" is generally not appropriate unless the label or prescriber says so. Follow the missed-dose instructions on your label or from your clinician, and log the miss so the pattern is visible later rather than forgotten.
For Liothyronine the useful record is the dose, the time it was actually taken, and what else was taken in the same window. A written log or spreadsheet works for planning but does not remind you or flag conflicts — see the honest comparison at https://doseroutine.com/vs/spreadsheet and the wider roundup at https://doseroutine.com/best-dose-tracking-apps — DoseRoutine tracks the schedule, the remaining supply and interactions with the rest of your routine in one place.
No. Liothyronine supplies T3, while levothyroxine supplies T4. Their milligram or microgram amounts are not interchangeable, and switching requires clinical interpretation of symptoms and thyroid tests.
No. The medicine information warns against using thyroid hormone for obesity or weight loss in people with normal thyroid function. Excess thyroid hormone can cause serious toxicity, including heart-related complications.
Added to levothyroxine as a fixed T4:T3 combination in the LEVOLIO study (totally thyroidectomized subjects); the Azizi et al. protocol describes a slow-release liothyronine formulation combined with levothyroxine, with the completed comparative-effectiveness trial titrating levothyroxine+liothyronine combinations to a target TSH. Route reported: Oral tablet. Frequency reported: Once or twice daily depending on the formulation and protocol cited. These are amounts documented in the cited studies and labels for Liothyronine — they are reported for reference, not a recommendation. Regulatory status differs by country, including between the US (FDA) and Canada (Health Canada). Confirm any amount with a licensed clinician before you take it.
Sources cited on this page
Specific documents referenced by the numbered markers above. Each number matches the marker in the text.
- PubChem CID 23724940(opens in a new tab)National Center for Biotechnology Information · pubchem.ncbi.nlm.nih.gov/compound/23724940
- MedlinePlus(opens in a new tab)U.S. National Library of Medicine · medlineplus.gov/druginfo/meds/a682462.html
Verify at
Publisher search links for Liothyronine. These are places to check the information — they are not citations, so they are not numbered.
- DrugBank(publisher search, opens in a new tab)DrugBank Online · publisher search
- NIH Office of Dietary Supplements(publisher search, opens in a new tab)National Institutes of Health · publisher search
- FDA-approved labeling (DailyMed)(publisher search, opens in a new tab)U.S. Food and Drug Administration · publisher search
- Cochrane Library(publisher search, opens in a new tab)Cochrane · publisher search
- PubMed literature search(publisher search, opens in a new tab)National Library of Medicine · publisher search
- Wikipedia entry(publisher search, opens in a new tab)Wikipedia · publisher search
DoseRoutine compiles summaries from publicly available scientific and regulatory references. Always verify important decisions with a licensed clinician. How we source and review this information.
What is the short answer on Liothyronine?
Plain-text summary, safe to quote verbatim:
Liothyronine, also known by its chemical abbreviation T3, is a synthetic form of the naturally occurring thyroid hormone triiodothyronine. It is available as a prescription medication and is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones.
Source: DoseRoutine — https://doseroutine.com/library/liothyronine
Liothyronine cheat sheet
DoseRoutine cheat sheet · Medication
Liothyronine
Liothyronine, also known by its chemical abbreviation T3, is a synthetic form of the naturally occurring thyroid hormone triiodothyronine. It is available as a prescription medication and is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones.
Evidence
Strong
2 human randomized trials and regulatory approval on file.
Studied range
Added to levothyroxine as a fixed T4:T3 combination in the LEVOLIO study (totally thyroidectomized subjects); the Azizi et al. protocol describes a slow-release liothyronine formulation combined with levothyroxine, with the completed comparative-effectiveness trial titrating levothyroxine+liothyronine combinations to a target TSH
Route
Oral tablet
Frequency studied
Once or twice daily depending on the formulation and protocol cited
Half-life
~25 h
Timing
in the morning
With food
on an empty stomach
Prescription only (US)Liothyronine (synthetic T3) is FDA-approved for hypothyroidism; its use in combination with levothyroxine remains an area of active clinical trial investigation rather than a settled first-line recommendation
Key references
- Randomized double-blind placebo-controlled trial on levothyroxine and liothyronine combination therapy in totally thyroidectomized subjects: the LEVOLIO study (2024)
- Comparative Effectiveness of Levothyroxine, Desiccated Thyroid Extract, and Levothyroxine+Liothyronine in Hypothyroidism (2021)
- Treatment of hypothyroidism with levothyroxine plus slow-release liothyronine: a study protocol for a randomized controlled double-blinded clinical trial (2025)
Studied ranges, not dosing advice. Not medical advice — talk to a clinician. doseroutine.com/library/liothyronine
Cite this page
Using this in an article, AI answer, or research note? Please attribute:
DoseRoutine. (2026). Liothyronine — Overview, Benefits & Side Effects. Retrieved from https://doseroutine.com/library/liothyronine
What compounds are similar to Liothyronine?
Others in the medication category or studied for the same goals.