Table 1. Future thyroid formulations and directives.

TRβ: thyroid hormone receptor beta; T3: triiodothyronine; T4: levothyroxine; NASH: nonalcoholic steatohepatitis; TRα: thyroid hormone receptor alpha; FDA: U.S. Food and Drug Administration

Therapy/Agent	Mechanism/Description	Potential Benefits	Limitations/Status
Sustained-release T3 (SR-T3)	Modified-release liothyronine designed to mimic the circadian T3 rhythm and reduce serum peaks	More stable T3 levels, fewer cardiac/mood side effects, closer to physiologic secretion	Limited availability; not yet FDA-approved; long-term data pending
TRβ-selective analogs (e.g., eprotirome, VK2809)	Synthetic agents selectively targeting TRβ to modulate liver/lipid metabolism	Lipid-lowering, liver fat reduction, and potential NASH application with fewer TRα-mediated side effects	Not approved for hypothyroidism; still in trials for metabolic diseases
Bioidentical compounded T3/T4	Custom-compounded formulations tailored to patient-specific T4:T3 needs, including slow-release options	Personalized dosing, improved symptom control in T4 non-responders	Variable compounding standards; lack of large-scale clinical data
Future directions (e.g., nanoparticle, transdermal delivery)	Experimental delivery systems aiming for tissue-specific targeting and improved absorption	Precision hormone delivery with minimal systemic peaks	Experimental stage; delivery mechanisms under development