Rankings / Hormones & Endocrine

T3 (liothyronine)

Hormones & Endocrine · Active thyroid hormone

Tier B-

Reviewed by Read Off Label · Last reviewed · How we grade

thyroidprescriptionmitochondrialwarning-only
6.2 / 10
Tier B-
Ev 8 Bn 8 Sf 3.5

Bottom line

Read Off Label grades T3 (liothyronine) as B- (6.2/10) based on strong evidence, high benefit magnitude, and a med-high-risk safety profile.

Often sought by patients who feel unwell on T4 monotherapy despite normal TSH.

Typical use: Clinical: 5-25 mcg/day, often divided, in T4/T3 combo therapy; supraphysiologic 25-100 mcg/day seen in off-label… — Rx.

What this is

Often sought by patients who feel unwell on T4 monotherapy despite normal TSH. AACE/ATA 2014 guidelines acknowledge T3 combination therapy as reasonable. Short half-life (~1 day) typically requires divided dosing. Off-label fat-loss use (supraphysiologic 25-100 mcg/day) is dangerous and not a sound strategy in euthyroid individuals: it suppresses endogenous thyroid function, drives muscle catabolism alongside fat loss, and discontinuation often causes rebound hypothyroidism — the cardiac (arrhythmia) and bone-loss consequences are the binding constraint.

Mechanism

Biologically active thyroid hormone; binds thyroid hormone receptors (TRα, TRβ); upregulates metabolic rate, lipolysis, protein turnover; shorter half-life (~1 day) than T4

Dose & route

Clinical: 5-25 mcg/day, often divided, in T4/T3 combo therapy; supraphysiologic 25-100 mcg/day seen in off-label fat-loss / bodybuilding cutting use (not advised)

Citations

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Common questions

Does T3 (liothyronine) work?
Read Off Label rates the evidence for T3 (liothyronine) as Strong and the benefit magnitude as high, producing an overall grade of B- (6.2/10). Often sought by patients who feel unwell on T4 monotherapy despite normal TSH.
Is T3 (liothyronine) safe?
T3 (liothyronine) has a med-high risk profile in published human data. Legal status: Rx (Cytomel). This is not medical advice — see the disclaimer.
What is the typical dose for T3 (liothyronine)?
Clinical: 5-25 mcg/day, often divided, in T4/T3 combo therapy; supraphysiologic 25-100 mcg/day seen in off-label fat-loss / bodybuilding cutting use (not advised)
How does T3 (liothyronine) work?
Biologically active thyroid hormone; binds thyroid hormone receptors (TRα, TRβ); upregulates metabolic rate, lipolysis, protein turnover; shorter half-life (~1 day) than T4

This is an independent synthesis of published research by a non-clinician. Scores are opinions supported by citations, not prescriptions. See the full disclaimer and methodology for how this score was produced and what it does and doesn't mean.