Impact of taking thyroxine with herbal brews

Background/Objectives: Herbal brews other than tea/coffee are becoming popular. We observed that these interfered with absorption of thyroxine. Since no prior studies have examined this, we sought to estimate this interaction effect, if any. Materials and Methods: This study was conducted among outpatients of a tertiary care hospital in India. Patients on thyroxine replacement were interviewed regarding the drink used with thyroxine. Various herbal brews used were compared against plain water. Thyroid-stimulating hormone was measured and compared. Results: Total of 121 patients fulfilled the inclusion and exclusion criteria, and 69 (57.0%) patients among them took thyroxine with a herbal brew. Various herbal products included cutch-tree (Karingali) 26 (37.7%), herbal mixture (Dahashamini) 28 (40.6%), and others 15 (21.7%). Risk of not achieving euthyroidism with any herbal brew was 7.6 times high (odds ratio [OR] 7·6 with 95% confidence interval [CI]: 3·1–18·5) as against plain water and was the highest for cutch, OR 12.4 with 95% CI: 4.0–38.0. Conclusions: Several patients take thyroxine with water brewed with herbal products. Effectiveness of thyroxine was greatly reduced when taken with herbal brews.