Answer
It makes the kidneys retain water. If fluid intake exceeds the body's needs, the retained water dilutes sodium in the blood.
Sources for this answer
- Desmopressin Spray 10 Micrograms/dose, nasal spray, solution — Current selected SmPCemc · Summary of Product Characteristics
- UK GovernmentUK Government · Reputable Web
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.