Quetiapine induced hypothyroidism is a rare side effect requiring either drug discontinuation or initiation of thyroid replacement therapy. We highlight the potential reversibility of quetiapine induced hypothyroidism in two such cases.

Two case reports.

Case 1.Quetiapine (200mg/day) was initiated to a psychotic female patient due to exaggeration of positive symptomatology. Although her thyroid function tests (TFTs) upon admission were normal after a month significant decreases in T3 and T4 level and an elevation in TSH was observed. 45 days later the TFT returned to normal, although she remained on quetiapine. Case 2. Quetiapine (300mg/daily) was prescribed to a bipolar male patient due to a mixed affective episode with a very good response. Despite his normal admission TFTs, three weeks later a decrease in total T4 and a marked increase in TSH was observed .45 days later, although no measures were taken, TFTs returned within reference range.

These are the first cases reporting reversibility of quetiapine induced hypothyroidism. TFTs alterations are dose related, relatively slight and linked to a positive history of thyroid abnormality. Our patients did not fulfil any of these criteria. Besides, hypothyroidism resolved although the antipsychotic therapy was continued and no thyroid replacement therapy was given. We suggest a careful thyroid monitoring for patients initiating quetiapine. However, physicians should wait in cases of thyroid dysfunction, since thyroid dysregulation may soon be resolved.