Levothyroxine dosage produces a predictable ratio of T4 increase per mcg consumed
the verdict
REFUTED
the evidence says no
confidence 16/100
The claim that levothyroxine dosage produces a predictable ratio of T4 increase is refuted by evidence showing that individual pharmacokinetics, variable intestinal absorption, and tissue-specific deiodination make dosing highly unpredictable.
Evidence against · 4
Replacement therapy for hypothyroidism with thyroxine alone does not ensure euthyroidism in all tissues, as studied in thyroidectomized rats.
1995 · cited by 292
Demonstrates that fixed doses of thyroxine fail to produce uniform, predictable tissue-specific T3 levels across organs.
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More against · 3
A Review of the Pharmacokinetics of Levothyroxine for the Treatment of Hypothyroidism
2010 · cited by 166
Highlights that the pharmacokinetics of levothyroxine are complex and under-appreciated, meaning dosing does not yield a simple predictable ratio.
Gastrointestinal Malabsorption of Thyroxine
2018 · cited by 160
Notes that gastrointestinal malabsorption, drug interactions, and individual variability heavily disrupt the predicted efficacy of T4 doses.
Levothyroxine Dose Adjustment to Optimise Therapy Throughout a Patient’s Lifetime
2019 · cited by 92
Emphasizes that initial dosing of levothyroxine varies greatly and requires ongoing, complex adjustments rather than a fixed predictable ratio.