Overreplacement

Overreplacement is the medical practice of giving a hormone replacement therapy at a dose that exceeds the body’s physiologic needs, resulting in features of hormone excess rather than restored normal function. It occurs when a deficient endogenous substance is substituted with too much of the substitute, or when monitoring fails to keep levels within the normal range. Overreplacement is typically discussed alongside underreplacement, which reflects insufficient dosing.

Common contexts involve thyroid, glucocorticoid, and growth hormone replacement. Thyroid overreplacement, often from levothyroxine, can lead to iatrogenic thyrotoxicosis with symptoms such as palpitations, weight loss, heat intolerance, and anxiety. Laboratory signs include a suppressed thyroid-stimulating hormone (TSH) and elevated free T4. Glucocorticoid overreplacement may cause Cushingoid features, hyperglycemia, hypertension, osteoporosis, and, in children, growth suppression. Growth hormone overreplacement can result in edema, insulin resistance, joint symptoms, and, over long periods, features of excess growth hormone.

Assessment relies on clinical evaluation and appropriate laboratory tests to verify that hormone levels fall within the expected physiologic range for age and condition. For thyroid replacement, TSH and free T4 are used; for adrenal replacement, morning cortisol or ACTH stimulation testing; for growth hormone, insulin-like growth factor 1 (IGF-1) levels.

Management centers on dose adjustment and gradual tapering when feasible. Preventive strategies include starting with conservative dosing, individualized titration, and regular monitoring, considering factors such as age, comorbidities, and potential drug interactions that affect absorption or metabolism.