Liotrix
Liotrix is a fixed 4:1 combination of synthetic levothyroxine (T4) and liothyronine (T3), marketed as Thyrolar for hypothyroidism. In bodybuilding it is used off-label as a cutting aid to raise metabolic rate, prized for delivering both storage and active thyroid hormone in a single tablet.
01 Overview
Liotrix supplies both thyroxine and triiodothyronine in a physiologic-like ratio, so it produces a steadier active-hormone level than T3 alone while still adding direct T3 to bypass slow peripheral deconversion. It is a genuine prescription drug with decades of clinical use in thyroid replacement.
Metabolic users adopt it to accelerate fat loss during a calorie deficit. As with all exogenous thyroid hormone, supraphysiologic dosing suppresses endogenous TSH and can drive muscle loss, tachycardia and negative nitrogen balance, so it is not benign despite its clinical pedigree.
02 Mechanism
T4 and T3 bind nuclear thyroid hormone receptors, upregulating transcription of genes governing basal metabolic rate, thermogenesis, lipolysis and substrate oxidation. Excess hormone raises resting energy expenditure above baseline.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Cutting (off-label) | 1–2 grain/day | Oral | Supraphysiologic; titrate slowly, monitor heart rate |
| Replacement | 30–120 mg/day | Oral | Thyrolar grains; 1 grain = 50 mcg T4 + 12.5 mcg T3 |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Increased metabolic rateHigher resting energy expenditure accelerates fat loss in a deficit. | +10-30% BMR at supraphysiologic doses | Clinical | |
| Improved lipid oxidationThyroid hormone upregulates hepatic LDL receptors and fat mobilisation. | Lower LDL/total cholesterol | Clinical | |
| Resolution of hypothyroid symptomsRestores energy, thermogenesis and cognition in genuine deficiency. | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Tachycardia and palpitationsElevated resting heart rate, palpitations and arrhythmia risk. | Moderate | Common at high doses | Clinical | |
| Muscle catabolismLean mass loss when hormone is supraphysiologic and calories are low. | Moderate | Common in deficit | Clinical | |
| TSH suppressionExogenous hormone suppresses pituitary TSH and endogenous output. | Moderate | Universal supraphysiologic | Clinical |