Pharmaceuticals/Chemicals
T3 (Triiodothyronine)
Also called Liothyronine · Cytomel · T3
T3 comes up in bodybuilding for faster cutting and questions about thyroid levels during growth-hormone use. It is a thyroid-replacement medicine, not a selective fat burner; extra thyroid hormone can bring heart problems and muscle weakness.
Dosage & duration
Medical thyroid-replacement context only; this is not a weight-loss regimen.
Cytomel · adult hypothyroidism label
Product label- Dose
- Usual start:25 micrograms; usual maintenance:25–75 micrograms daily
- How often
- By mouth once daily
- How long
- Ongoing when indicated, with thyroid-function review
Medical replacement only, not a cutting dose. Older adults and people with cardiac disease have lower label starting doses; treatment is individualized.
Sources: 2
The practical difference
Replacement and cutting differ
| Context | Thyroid replacement | Weight-loss use |
|---|---|---|
| Goal | Replace missing thyroid hormone | Sought for faster cutting |
| Cytomel label | Treats diagnosed thyroid deficiency | Warns against use for weight reduction |
Why do bodybuilders look at T3?
The appeal is getting past a cutting stall while keeping muscle. Some people also ask whether growth-hormone use makes thyroid medication necessary. Those are reasons people investigate T3, not evidence that either situation needs it.
Will it target fat and preserve muscle?
Community reports disagree about strength, a flatter appearance and muscle loss. They cannot separate the drug from dieting and other compounds. The Cytomel label warns against weight-loss use: normal replacement amounts do not produce weight reduction in people with normal thyroid function, while excess can cause serious toxicity, including muscle weakness and heart problems.
Does using HGH mean you need T3?
Using growth hormone is not itself a thyroid diagnosis. Liothyronine treatment is assessed through the clinical situation and thyroid tests; neither a fat-loss stall nor a temperature reading provides a personal dose. T3 and T4 also have different treatment roles and are not interchangeable amounts.
What the plot can explain
The relative curve illustrates an assumed rise and fall after entries. It does not measure thyroid function, predict fat loss or establish a bodybuilding cycle. Keep micrograms and milligrams distinct when reading amounts.
Model details: T3 (Triiodothyronine) · relative timing
Compare timing and buildup for this compound. The values are not blood concentrations or a measure of strength.
Shows a relative timing scenario; absolute blood concentrations are not calibrated.
Timing assumptions and sources
Jonklaas 2015 observed timing;22 h depends on chosen late timepoints and endogenous physiology.
One 1 mg input peaks at 1 relative unit after a single dose. Other amounts scale proportionally; overlapping doses add when accumulation is on. Different compounds use separate relative scales.
- Timing half-life used
- 22.04 hours
- Absorption half-life assumed
- 0.4320654 hours
- Reference amount for the relative scale
- 1 mg
- The faster rate is inferred to match the 2.5 h source-scoped peak time; absorption half-life 0.4320654238413822 h is a mathematical shape parameter, not separately measured.
- A single 1-unit input has a peak of 1 relative unit; scaling and repeated-dose addition are mathematical assumptions. This normalization is independent of the example dose.
- Use 0.05 mg=50 mcg, not 50 mg.
- Endogenous suppression/redistribution mean subtracting one fixed baseline is not a complete repeated-dose exogenous model.
- Peak-normalized one-compartment AUC 0–24=4046,2.18×observed.
- Jonklaas et al 2015: single-dose T 3
Table 3:50 mcg, total Cmax 346, baseline 120, Tmax 2.5 h, baseline-corrected AUC 0–24=1860 ng·h/d L, half 22.04 h.
t3-triiodothyronine-relative-timing-2026-10 · version 1
Common questions
Does T3 burn only fat?
No. Excess thyroid effect is not selective for fat; muscle weakness and other effects can occur.
Is 25–75 micrograms a fat-loss recommendation?
No. That is the Cytomel label’s usual adult hypothyroidism maintenance context. It must not be relabelled as a cutting range.
Sources Labels, studies and notes behind this guide
Catalog evidence: Other human research. This describes the type of evidence, not a clinical review of every claim.
Summary and fact source checks: 2026-10-10, 2026-10-07. This records source checking, not medical review of the whole page.
Notes on the quick facts
- Medical purpose
- The treatment goal is normal function, not the highest metabolic rate.
- Physique interest
- The label specifically warns against using T3 for weight reduction.
- Critical unit
- A thousand-fold unit difference can be dangerous.
- 1. Cytomel — current prescribing information
April 2025 label: thyroid replacement, weight-loss boxed warning, laboratory assessment, muscle weakness and cardiac adverse effects.
- 2. Cytomel — US prescribing information
Adult hypothyroidism:25 mcg once daily usual starting dose; 25–75 mcg daily usual maintenance, with lower starts in elderly/cardiac disease. Explicit boxed warning against obesity/weight-loss use; arrhythmia and muscle-weakness risks.
- 3. MedlinePlus — liothyronine
Government patient information: thyroid replacement and potentially serious toxicity when used for weight reduction, especially alongside amphetamines.
- 4. Jonklaas et al 2015: single-dose T 3
Table 3:50 mcg, total Cmax 346, baseline 120, Tmax 2.5 h, baseline-corrected AUC 0–24=1860 ng·h/d L, half 22.04 h.
- 5. Cytomel US prescribing information
Liothyronine label: thyroid indications, microgram tablet strengths and boxed warning against weight-loss use.
- 6. Jonklaas et al., single-dose T3 kinetics
50 microgram Thyromax study in 12 healthy volunteers: T3 peaked at 2.5 hours; TSH response persisted longer. Not a fat-loss or standard Cytomel dosing trial.
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