Objective Individuals requiring psychiatric emergency services are often highly distressed and intoxicated. To provide an objective and comprehensive measure of their stress-related physiological dysregulations, we indexed allostatic load with 14 biomarkers collected within 24 h of patients' admission to the largest psychiatric hospital in the Canadian province of Quebec. Methods This study (N = 278) combines data for emergency patients (n = 76; 65.8% women; M age = 44.97, SE = 1.6) and hospital workers who served as sex- and age-matched controls (n = 202; 70.8% women; M age = 40.10, SE = 0.83). Sex-specific allostatic load indices summarized neuroendocrine (cortisol), immune (tumor necrosis factor-α, interleukin-6, c-reactive protein), metabolic (insulin, glycosylated hemoglobin, total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, body mass index), and cardiovascular (heart rate, systolic and diastolic blood pressure) functioning. Well-validated questionnaires assessed substance (ab)use. Results Individuals presenting at psychiatric emergency showed elevated allostatic load, drug abuse, and tobacco use compared to controls. Elevated allostatic load in emergency patients was driven by elevated cortisol, interleukin-6, systolic blood pressure, and heart rate; however, allostatic load was not explained by substance (ab)use or demographic variables. Sub-group analyses revealed that emergency patients primarily diagnosed with bipolar, depressive, or anxiety disorders showed higher allostatic load than those diagnosed with personality disorder(s). Conclusions This study demonstrates that individuals presenting at psychiatric emergency services show physiological dysregulations associated with chronic stress. Future research should explore the clinical utility of allostatic load in predicting comorbidities among psychiatric patients.