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Liothyronine (Cytomel / T3)

Thyroid Hormoneprescriptionoral · inferred

Synthetic triiodothyronine (T3), the active thyroid hormone. 3-5x more potent than T4 (levothyroxine) with faster onset (hours vs days). Used for hypothyroidism (alone or combined with T4), myxedema coma, and T3 suppression testing. Narrow therapeutic index with cardiac risk (tachycardia, arrhythmia) at supratherapeutic levels. ~95% oral bioavailability. Serum T3 peaks within 2-4 hours, causing wider daily fluctuations than T4 monotherapy.

Projected serum levels — 25 mcg (≈ 0.025 mg), once daily

Liothyronine (Cytomel / T3)
Liothyronine (Cytomel / T3) modeled serum levels, 25 mcg (≈ 0.025 mg) once daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 3 days. 0 0.25 0.50 0.75 1 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 3
Liothyronine (Cytomel / T3) modeled serum levels with a loading dose of 49.0 mcg, then 25 mcg (≈ 0.025 mg) once daily The first dose is larger so levels approach steady state faster. 0 0.25 0.50 0.75 1 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule

Maintenance schedule: 25 mcg (≈ 0.025 mg) once daily (oral).

Loading schedule: 49.0 mcg on day 1, then 25 mcg (≈ 0.025 mg) once daily — reaching therapeutic levels sooner.

Modeled steady state after ~3 days: peak ≈ 0.044 mg, trough ≈ 0.023 mg body load. Population-based estimate over 15 days for a reference dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Thyroid Hormone
Route modeled
Oral
Model confidence
inferred
Half-life
24 h
Common dose
25 mcg (≈ 0.025 mg)
Suggested maximum
75 mcg/day
Reference dose range
0.005–75 mcg (single dose)
Suggested cadence
once daily
Validated against
0.050 mg oral — Cmax 0.003 mg/L at 2 h

Documented interactions

  • danger
    Levothyroxine (Synthroid) + Liothyronine (Cytomel / T3) Protein binding

    Liothyronine (Cytomel / T3) may displace Levothyroxine (Synthroid) from plasma protein binding sites, transiently raising free drug concentration. This drug has a narrow therapeutic index; free…

  • warning
    Apigenin + Liothyronine (Cytomel / T3) Protein binding

    Apigenin may displace Liothyronine (Cytomel / T3) from plasma protein binding sites, transiently raising free drug concentration.

  • warning
    Aripiprazole (Abilify) + Liothyronine (Cytomel / T3) Protein binding

    Aripiprazole (Abilify) may displace Liothyronine (Cytomel / T3) from plasma protein binding sites, transiently raising free drug concentration.

  • warning
    Armour Thyroid (Desiccated Thyroid Extract) + Liothyronine (Cytomel / T3) Protein binding

    Liothyronine (Cytomel / T3) may displace Armour Thyroid (Desiccated Thyroid Extract) from plasma protein binding sites, transiently raising free drug concentration.

  • warning
    Astaxanthin + Liothyronine (Cytomel / T3) Protein binding

    Astaxanthin may displace Liothyronine (Cytomel / T3) from plasma protein binding sites, transiently raising free drug concentration.

  • warning
    Atomoxetine (Strattera) + Liothyronine (Cytomel / T3) Protein binding

    Atomoxetine (Strattera) may displace Liothyronine (Cytomel / T3) from plasma protein binding sites, transiently raising free drug concentration.

Serum checks 145 modeled interaction pairings for liothyronine (cytomel / t3) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Effects of thyroxine as compared with thyroxine plus triiodothyronine in patients with hypothyroidism Bunevicius R et al. · New England Journal of Medicine, 1999 DOI

    First RCT demonstrating T4+T3 combination therapy improved mood, cognition, and well-being compared to T4 monotherapy in hypothyroid patients, though subsequent larger trials showed mixed results.

  2. Pharmacokinetics of liothyronine (L-T3) in healthy volunteers Jonklaas J et al. · Thyroid, 2015 DOI

    Controlled PK study establishing liothyronine half-life of ~25 hours, tmax of 2-4 hours, near-complete oral absorption, and quantifying the peak-to-trough serum T3 variability with different dosing frequencies.

2 published studies referenced in the app, each with a plain-language summary.