Tolvaptan is an oral medication prescribed for treating hyponatremia due to conditions like SIADH and autosomal dominant polycystic kidney disease (ADPKD). It functions by binding to and inhibiting vasopressin V2 receptors in the renal collecting ducts, promoting aquaresis—the excretion of free water without losing electrolytes—and helping to restore water balance. In the context of ADPKD, tolvaptan slows the progression of kidney function decline in adults at high risk of rapid disease advancement by reducing cyst growth and kidney volume, which may help delay or prevent the need for dialysis or kidney transplantation. The drug is also approved for the treatment of clinically significant hypervolemic and euvolemic hyponatremia associated with conditions such as SIADH, liver cirrhosis, and heart failure. Tolvaptan has notable pharmacokinetic properties, including a stereospecific ratio of the S-(-) to R-(+) enantiomer. It is primarily bound to plasma proteins and metabolized in the liver by CYP3A4, with its metabolites being inactive. The drug is mainly excreted in feces (59%), with a smaller amount eliminated through urine (40%). Its elimination half-life is around 12 hours, supporting a once-daily dosing regimen. Several analytical methods have been developed to detect tolvaptan in human plasma, including the extraction of the analyte and internal standard, chromatographic separation on a C18 column, the creation of a linear calibration curve, forced degradation studies, high-performance liquid chromatography coupled with tandem mass spectrometry for drug detection, electrochemical behavior analysis, and optimization of self-microemulsifying drug delivery systems