Date of Award


Document Type

Scholarly Project

Degree Name

Master of Physician Assistant Studies (MPAS)


Physician Assistant Studies

First Advisor

Jay Metzger


Desiccated thyroid hormone; Hypothyroidism; Thyroid hormone replacement; Combination; DTE; Liothyronine


The nature of this systemic literature review and research is to explore the use of thyroxine (T4) monotherapy versus T4 and triiodothyronine (T3) (combination) therapy for the treatment of hypothyroidism. A literature review was conducted using electronic search databases which included PubMed, CINHAL, and Clinical Key. Mesh terms included hypothyroidism/drug therapy, hypothyroidism/diagnosis, thyroid hormones/physiology, and thyroxine. Filters applied to the search included clinical study, clinical trial, guideline, journal article, meta-analysis, randomized controlled study, and systematic review. The search was tapered by limiting results to the last ten years, human species, and adults 19+. The articles were further narrowed by excluding subclinical hypothyroidism and pregnancy. For this review, 21 resources were selected. The reviewed clinical studies resolved that combination and monotherapy are analogous in the general population despite commonly observed trends in those utilizing combination therapy: modest weight loss and subjective improved well-being. Regardless, most investigators deemed no benefit of implementing combination therapy over levothyroxine. Monotherapy remains the appropriate treatment for the general population of primary hypothyroid patients, as the majority experience positive outcomes with this regimen. Yet, combination therapy should not be entirely excluded and should be considered in patients who fail to respond appropriately to monotherapy. It also should be contemplated as a preliminary regimen in this population. Modest changes observed have often been considered trivial and clinically insignificant to investigators but can be substantial to modern patients. Though these perceived moderate improvements may only be observed in a select population, it does not yield them any less significant.