Physuline is an oral vasopressin V2-receptor antagonist drug that has proven effective in patients with syndrome of inappropriate antidiuretic hormone (SIADH), a condition resulting in fluid overload due to the excessive release of antidiuretic hormone.

Current views maintain that the role of hormones in the salivary glands--particularly aldosterone and antidiuretic hormone is solely to modify the ionic content of the saliva.

This is due to two factors: 1) all such drinks are hypotonic (<135 mmol/L), and therefore will cause dilution of serum [Na+] if water is retained in the body to excess; and 2) it is well known that even administration of isotonic saline will not increase serum [Na+] in hyponatremic patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) because in a euvolemic or hypervolemic state, the infused sodium will be excreted in the urine rather than retained (65).