The goal of this observational study is to explore the prevalence of hypercortisolism in a population with difficult to control type 2 diabetes despite receiving standard-of-care therapies. Additionally, the study will evaluate the correlation between salivary cortisol levels and glycemic control.

Despite advanced treatments, many individuals with type 2 diabetes develop refractory disease, leading to poor glycemic control and a higher risk of complications. Hypercortisolism, which promotes hyperglycemia, may be a key contributing factor. A recent study found a 23.8% prevalence of hypercortisolism in patients with difficult to control type 2 diabetes, linking the condition to higher rates of cardiovascular disease. As stable salivary cortisol testing can effectively screen for this condition, this study has two aims. First, the study will evaluate the prevalence of hypercortisolism in patients with difficult to control type 2 diabetes and identify its associated risk factors. Second, the study will establish the correlation between salivary cortisol and glycemic levels in this population.

Inclusion Criteria:

1. Aged between 18 and 80 years.
2. Meets the definition of difficult to control type 2 diabetes:

HbA1c level between 7.5% and 11.5%, AND Taking 3 or more anti-hyperglycemic drugs. OR Taking insulin and other anti-hyperglycemic drugs. OR Taking 2 or more anti-hyperglycemic drugs AND a.) the presence of 1 or more micro-vascular or macro-vascular complication (retinopathy, diabetic nephropathy and chronic kidney disease, diabetic neuropathy, atherosclerotic heart disease with diabetes); AND/OR b.) concomitant hypertension requiring 2 or more anti-hypertension medications.

Exclusion Criteria:

1. Patients with Type 1 diabetes, new-onset diabetes (<1 year duration), or other specific types of diabetes.
2. History of systemic glucocorticoid use within the last 3 months (inhaled or topical agents are not exclusionary).
3. Pregnant or lactating.
4. Presence of severe cardiac, hepatic, renal, or other major organ dysfunction.
5. History of acute diabetic complications, such as diabetic ketoacidosis or hyperosmolar hyperglycemic state, within the last 3 months.
6. Presence of diseases that significantly affect metabolism, such as malignancy or autoimmune disorders.
7. Inability to tolerate adhesive tape, severe skin conditions at the sensor placement site, or presence of a psychiatric illness or cognitive impairment that would interfere with study compliance.
8. A known diagnosis of Cushing's syndrome, or currently receiving treatment with any of the following: mifepristone, metyrapone, osilodrostat, ketoconazole, fluconazole, aminoglutethimide, etomidate, octreotide, larazotide, long-acting octreotide, or pasireotide.
9. Excessive alcohol consumption (defined as >14 units per week for males or >7 units per week for females).
10. Severe, untreated sleep apnea.
11. Night shift workers (defined as being awake between 11:00 PM and 7:00 AM).
12. Known allergy or severe reaction to dexamethasone.

The participants are enrolled from the Department of Endocrinology and Metabolism from Shanghai Sixth People's Hospital.