RecruitingPhase 3Drug trialHYDROchlorothiazide to PROTECT Polycystic Kidney Disease Patients and Improve Their Quality of LifeAutosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive formation of renal cysts which ultimately lead to a loss of renal function. Tolvaptan (a V2R antagonist) is currently the only effective treatment for preserving renal function in ADPKD. However, side-effects such as polyuria limit its tolerability and thereby the therapeutic potential. This study will test whether co-administration with hydochlorothiazide can improve V2RA efficacy (slowing kidney function decline) and tolerability (quality of life) in ADPKD. Approximately 300 patients will be enrolled.