This a clinical study to improve medication adherence among patients with hypertension in Switzerland. Adult men and women who suffer from high blood pressure and have been prescribed a therapy consisting of at least 4 tablets per day can participate in this study. The investigators intend to examine whether Collabree, a mobile phone application, is effective in supporting patients with hypertension to more successfully following their therapy plan. The study will also investigate if the use of Collabree can help lower blood pressure. The study consists of 4 visits that take place during a 90-day adherence promotion program plus a 90-day follow-up period. There is also a screening visit before the study to determine whether the participants qualify for the study. The visits are carried out at the University Hospital Basel. Each visit lasts about 1-2 hours. During the visits, blood pressure is measured in the clinic and also through 24-hour ambulatory blood pressure monitoring (ABPM). Participants will also fill out questionnaires. Participants are randomly assigned to one of 3 groups in a ratio of 1: 1: 1. Two of these groups will receive the Collabree mobile phone application. All participants will receive a box for storing their antihypertensive medication. This box serves as a system for measuring medication intake as it records the time the box is opened and closed. Standard care will given to all participants.