Endocrine Abstracts

Isolated central hypothyroidism in adults is extremely rare, though emerging data suggest that antidepressant drugs may occasionally alter the hypothalamic–pituitary–thyroid axis. We present three adult cases referred for nonspecific symptoms who were found to have abnormal thyroid function tests (TFTs) while taking antidepressant medications. The first, a 40-year-old woman on olanzapine, venlafaxine and mirtazapine, had normal TFTs until early 2025, when fT4 was repeatedly low (7.1-7.5 pmol/l), with inappropriately normal TSH (1.55-2.99 mUI/l), normal fT3 and negative TPO-Ab. The second, a 36 year old man on clomipramine, quetiapine, mirtazapine, and fluvoxamine, showed persistently low fT4 (5.1–8.8 pmol/l) since 2022 with TSH between 0.7–1.4 mIU/l, and an otherwise intact pituitary profile. The third, a 48 year old woman on Sertraline, had annual normal TFTs until recent testing, which revealed fT4 7.8 pmol/land TSH 2.8 mIU/l. None used lithium, amiodarone, steroids, or checkpoint inhibitors. These findings raise concern for antidepressant/antipsychotic induced central hypothyroidism. Existing literature supports this condition, particularly for sertraline or tricyclic antidepressants. In addition, a retrospective study indicated an increased risk of hypothyroxinaemia in patients taking mirtazapine. No consensus exists on management, but case reports suggested recovery of thyroid function when the offending medication is discontinued. Given minimal symptoms, which may be attributed to depressive disorder, the relative stable TFTs, and the potential reversible cause, we opted for conservative management. In conclusion, an increased awareness regarding potential interaction of psychotropic medication and thyroid function could prevent unnecessary imaging, overtreatment and patient anxiety regarding a new diagnosis.