It is defined as less-than-maximally-dilute urine in the presence of plasma hypo-osmolality (hyponatremia) without volume depletion or overload, emotional stress, pain, diuretics, or other drugs that stimulate vasopressin secretion (eg, chlorpropamide, carbamazepine, vincristine, clofibrate, antipsychotic drugs, aspirin, ibuprofen) in patients with normal cardiac, hepatic, renal, adrenal, and thyroid function.