Context Neurohypophysis (NH) function in eating disorders (ED) remains poorly elucidated. Studies on vasopressin and oxytocin display inconclusive findings regarding their levels and associations with psychological complications in ED. The profile of opioid tone, a crucial NH activity regulator, is also unknown. Objective To characterise the circadian profile of NH hormones and NH opioid tone using positron emission tomography/MRI (PET/MRI) imaging in patients with ED compared to healthy controls. Methods Twelve‐point plasma circadian profiles of copeptin and oxytocin, alongside nutritional and psychological scores, were assessed in age‐matched female participants: 13 patients with anorexia nervosa restrictive‐type (ANR), 12 patients recovered from AN (ANrec), 14 patients with bulimia nervosa and 12 controls. Neurohypophysis PET/MRI [ 11 C] diprenorphin binding potential (BP ND ) was evaluated in AN, ANrec and controls. Results Results revealed lower copeptin circadian levels in both ANR and ANrec compared to controls, with no oxytocin differences. Bulimia nervosa exhibited elevated copeptin and low oxytocin levels. [ 11 C] diprenorphin pituitary binding was fully localised in NH. Anorexia nervosa restrictive‐type displayed lower NH [ 11 C] diprenorphin BP ND (indicating higher opioid tone) and volume than controls. In ANR, copeptin inversely correlated with osmolarity. Neurohypophysis [ 11 C] diprenorphin BP ND did not correlated with copeptin or oxytocin. Conclusion Copeptin demonstrated significant group differences, highlighting its potential diagnostic and prognostic value. Oxytocin levels exhibited conflicting results, questioning the reliability of peripheral blood assessment. Increased NH opioid tone in anorexia nervosa may influence the vasopressin or oxytocin release, suggesting potential therapeutic applications.