Thyroid Hormone Administration and Cortisol Metabolism

Introduction to Thyroid Hormone-Induced Cortisol Breakdown

Thyroid hormone administration increases cortisol breakdown primarily by accelerating cortisol metabolism through enhanced hepatic enzyme activity, which can potentially precipitate an adrenal crisis in patients with undiagnosed adrenal insufficiency 1, 2

When multiple pituitary hormones are deficient, hydrocortisone must be replaced first before thyroid hormone to prevent adrenal crisis 1, 2
If thyroid hormone is replaced first when cortisol is low, the increase in cortisol metabolism can trigger a potentially life-threatening adrenal crisis 1, 3

Always evaluate for adrenal insufficiency when central hypothyroidism is suspected 1
In patients with suspected combined pituitary hormone deficiencies, check morning cortisol levels before initiating thyroid hormone replacement, and if morning cortisol is low, start hydrocortisone replacement before initiating thyroid hormone replacement 3
Wait at least one week after starting hydrocortisone before initiating thyroid hormone replacement 3
Monitor patients closely during the initial phase of thyroid hormone replacement for signs of increased cortisol clearance 4

Patients taking enzyme-inducing medications along with thyroid hormone may experience even faster cortisol metabolism 4, 5
Hyperthyroid patients may require higher doses of hydrocortisone if they have concurrent adrenal insufficiency 4
Patients receiving immune checkpoint inhibitor therapy are at particular risk for developing both thyroid dysfunction and adrenal insufficiency, requiring careful monitoring of both axes 6, 7