SUN-387 Difference in Clinical Symptoms between Generic and Branded Thyroid Preparations

Abstract Disclosure: C.M. Barrera: None. K. Sanabria: None. Context: The United States Food and Drug Administration established levothyroxine bioequivalence to make levothyroxine preparations interchangeable. Owing to multiple variables, interchangeability has not been achieved. Currently, dose adjustment is the only recommendation to offset symptoms developed after any medication change. Objective: Routine office patients on generic levothyroxine with anxiety were offered a branded equivalent dose.Design: Patients who were switched to branded equivalents took the PROMIS short-form anxiety scale and were categorized into three groups. Group 1 showed improved anxiety, Group 2 showed no difference, and Group 3 showed worsened anxiety. Data between generic and branded levothyroxine patients for PROMIS raw scores and TSH/T4 levels in Groups 1, 2, and 3 were analyzed using one-way analysis of variance.Main Outcome: 49 patients (female/male:46/3) were recruited from routine office visits. The mean PROMIS score in Group 1 (N = 33) on generic and branded (mean ± SD) was 25.76 ± 5.58 and 13.27 ± 4.91; p < 0.001, respectively, in Group 2 (N = 13) on generic and branded was 16.31 ± 5.72 and 15.77 ± 5.89; p = 0.82, respectively, and in Group 3 (N = 3) on generic and branded was 7 ± 0.0 and 28 ± 10.44; p < 0.03. After switching brands, 23.5% had dose adjustments before taking the PROMIS scale and measuring TSH and T4. No statistically significant difference in TSH and T4 was observed between generic and branded patients in Groups 1, 2, and 3.Post-hoc Cohen’s d power analysis on PROMIS scale in Group 1= 2.38, Group 2 = 0.09, Group 3 = 2.85. Learning Point: 1. Resolution of chronic anxiety in Group 1 was achieved after switching from generic to branded levothyroxine. There was no statistically significant change in TSH and T4 to explain the anxiety.2. Branded levothyroxine in Group 3 can worsen anxiety compared to generic in a minority of patients.3. Post hoc Cohen’s d was highly significant for Groups 1 and 3, suggesting these results apply to a broader population.4. Monitoring symptoms when treating hypothyroidism is essential, and beyond dose adjustment, changing thyroid preparations is a new tool available to the practicing clinician. References: 1.Hennessey JV. Generic vs. name brand L-thyroxine products: interchangeable or still not? J Clin Endocrinol Metab. 2013;98(2):511-514. 2.Benvenga S, et al. Levothyroxine formulations: pharmacological and clinical implications of generic substitution. Adv Ther. 2019 Sep;36(Suppl 2):59-71.3.Fliers E, et al. European thyroid association (ETA) and thyroid federation international (TFI) joint position statement on the interchangeability of levothyroxine products in EU countries. Eur Thyroid J. 2018;7(5):238-242. 4.Tarescavage AM, et al. Construct validity of DSM-5 level 2 assessments (PROMIS depression, anxiety, and anger): evidence from the MMPI-2-RF. Assessment. 2021;28(3):788-795. Presentation: Sunday, July 13, 2025