Evaluating the effectiveness of combined T4 and T3 therapy or desiccated thyroid versus T4 monotherapy in hypothyroidism: a systematic review and meta-analysis

Abstract

Background: Persistent symptoms in hypothyroid patients despite normalized TSH levels suggest the need for alternative treatments. This study aims to evaluate the effectiveness of combined T4 and T3 therapy or desiccated thyroid (DTE) compared to T4 monotherapy, with a focus on thyroid profile, lipid profile, and quality of life metrics.

Methods: We conducted a systematic review in Embase, Medline/PubMed, and Web of Science up to 11/23/2023. We used the following keywords: "Armour Thyroid," OR "Thyroid extract," OR "Natural desiccated thyroid," OR "Nature-Throid," "desiccated thyroid," OR "np thyroid," OR "Synthroid," OR "levothyroxine," OR "Liothyronine," "Cytomel," OR "Thyroid USP," OR "Unithroid." AND "hypothyroidism. " We only included RCTs and excluded non-RCT, case-control studies, and non-English articles.

Results: From 6,394 identified records, 16 studies qualified after screening and eligibility checks. We included two studies on desiccated thyroid and 15 studies on combined therapy. In this meta-analysis, combination therapy with T4 + T3 revealed significantly lower Free T4 levels (mean difference (MD): -0.34; 95% CI: -0.47, -0.20), Total T4 levels (mean difference: -2.20; 95% CI: -3.03, -1.37), and GHQ-28 scores (MD: -2.89; 95% CI: -3.16, -2.63), compared to T4 monotherapy. Total T3 levels were significantly higher in combined therapy (MD: 29.82; 95% CI: 22.40, 37.25). The analyses demonstrated moderate to high heterogeneity. There was no significant difference in Heart Rate, SHBG, TSH, Lipid profile, TSQ-36, and BDI Score. Subjects on DTE had significantly higher serum Total T3 levels (MD: 50.90; 95% CI: 42.39, 59.42) and significantly lower serum Total T4 (MD: -3.11; 95% CI: -3.64, -2.58) and Free T4 levels (MD: -0.50; 95% CI: -0.57, -0.43) compared to T4 monotherapy. Moreover, DTE treatment showed modestly higher TSH levels (MD: 0.49; 95% CI: 0.17, 0.80). The analyses indicated low heterogeneity. There was no significant difference in Heart Rate, SHBG, Lipid profile, TSQ-36, GHQ-28, and BDI Score.

Conclusions: Our study revealed that combined therapy and DTE lead to higher T3 and lower T4 levels, compared to T4 monotherapy in hypothyroidism. However, no significant effects on heart rate, lipid profile, or quality of life were noted. Given the heterogeneity of results, personalized treatment approaches are recommended.

Keywords: Desiccated thyroid extract; Hypothyroidism; Levothyroxine; Liothyronine.

Fig. 1

PRISMA Flow diagram of literature search and study selection process

Fig. 2

Forest plots illustrating the effects of combined T4 + T3 therapy vs. T4 monotherapy on TSH, Total T4, Free T4, Total T3, Heart rate, and SHBG levels

Fig. 3

Forest plots illustrating the effects of combined T4 + T3 Therapy vs. T4 Monotherapy on lipid profiles, quality of life, and mental health outcomes

Fig. 4

Forest plots illustrating the effects of DTE therapy vs. T4 monotherapy on lipid profiles, quality of life, and mental health outcomes

Fig. 5

Forest plots illustrating the effects of DTE therapy vs. T4 monotherapy on lipid profiles, quality of life, and mental health outcomes

Fig. 6

Forest plots illustrating the effects of DTE therapy vs. T4 monotherapy on IMI and DMI