levothyroxine vs liothyronine
PlainMeds reviewed this comparison against our methodology in August 2026. It places FDA and CMS record fields side by side, without recommending either medication.
Side-by-side comparison of levothyroxine and liothyronine. Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
minor Known Drug Interaction
Other drugs: Amiodarone Amiodarone inhibits peripheral conversion of levothyroxine (T4) to triiodothyronine (T3) and may cause isolated biochemical changes (increase in serum free-T4, and decreased or normal free-T3) in clinically euthyroid patients.
Synthroid, Levoxyl, Tirosint
Cytomel
Levothyroxine is a medicine that replaces a hormone normally made by your thyroid gland. It is used when the thyroid doesn't make enough hormone on its own.
Liothyronine (Cytomel) is a medicine that replaces a thyroid hormone called T3. It helps your body work properly if you don't make enough thyroid hormone on your own.
This medicine treats hypothyroidism, a condition where the thyroid gland doesn't make enough thyroid hormone. It can be used in adults and children, even newborns. Levothyroxine can also be used after surgery and radioiodine therapy for thyroid cancer to help lower thyroid-stimulating hormone (TSH) levels.
This medicine treats hypothyroidism, a condition where your thyroid gland doesn't make enough thyroid hormone. It can also be used with surgery and radiation to manage thyroid cancer. Liothyronine can also be used for thyroid suppression tests to check for mild hyperthyroidism.
Levothyroxine provides a synthetic form of thyroxine (T4), which is the main hormone produced by the thyroid gland. Your body converts T4 into triiodothyronine (T3), the active form of the hormone. By providing T4, levothyroxine helps restore normal thyroid hormone levels in your body.
Liothyronine is a synthetic form of the T3 thyroid hormone. It works by increasing thyroid hormone levels in your body. This helps to regulate your body's metabolism and energy levels.
- • Fatigue
- • Increased appetite
- • Weight loss
- • Feeling hot
- • Headache
- • Fatigue
- • Increased appetite
- • Weight loss
- • Feeling hot
- • Fever
- Fatigue 25,847
- Nausea 22,026
- Headache 18,797
- Diarrhoea 18,176
- Dyspnoea 16,216
- Headache 859
- Fatigue 816
- Nausea 569
- Dyspnoea 549
- Pain 469
Thyroid hormones, including levothyroxine, should not be used for weight loss or to treat obesity. Using high doses can cause serious and life-threatening side effects, especially when taken with stimulant medicines.
This medicine should not be used for weight loss or to treat obesity. Taking high doses of thyroid hormone for weight loss can cause serious and life-threatening side effects, especially when taken with stimulant medicines.
Tell your doctor if you are pregnant or plan to become pregnant. Your levothyroxine dose may need to be adjusted during pregnancy. Levothyroxine passes into breast milk, but it is not expected to harm the baby.
Tell your doctor if you are pregnant or plan to become pregnant. Your dose of liothyronine may need to be adjusted during pregnancy. This medicine passes into breast milk, but it is not expected to harm your baby.
How to Read This levothyroxine vs liothyronine Comparison
levothyroxine is classified in the Thyroid Hormone drug class, while liothyronine sits within the Thyroid Hormone (T3) class. Drugs from different classes work through distinct mechanisms, so a head-to-head comparison illustrates trade-offs rather than equivalence. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, levothyroxine has 101,062 submissions while liothyronine has 3,262. Those figures reflect cumulative reporting volume, not per-patient risk, so older, widely dispensed drugs typically look worse on count alone. These two drugs have a known minor interaction flagged in FDA labeling, attributed to this interaction can stop your body from turning one type of thyroid hormone into another, which can change your blood test results.. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot represent individual circumstances. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This registry does not provide medical, treatment, substitution, or medication-change directions for levothyroxine or liothyronine.
Registry boundary: This comparison displays source-record fields and does not provide individualized medical direction.