Journal of Medical Internet Research - International Scientific Journal for Medical Research, Information and Communication on the Internet #Preprint #PeerReviewMe: Warning: This is a unreviewed preprint. Readers are warned that the document has not been peer-reviewed by expert/patient reviewers or an academic editor, may contain misleading claims, and is likely to undergo changes before final publication, if accepted, or may have been rejected/withdrawn. Readers with interest and expertise are encouraged to sign up as peer-reviewer, if the paper is within an open peer-review period. Please cite this preprint only for review purposes or for grant applications and CVs (if you are the author). Background: Hypertension is a chronic disease that is considered to be a public health problem and requires efforts by patients to manage themselves. The global growth in the use of smartphones and tablets has been accompanied by the increased use of health applications. Many of these applications (‘apps’) support the self-management of hypertension, so they have potential benefits for lowering blood pressure (BP). Yet, a synthesis of the evidence for their effectiveness, their usability and patients’ satisfaction with their use in this population has not been conducted. Objective: A systematic review was conducted to assess the effectiveness of apps in lowering BP, as well as their usability and patients’ satisfaction with their use. Methods: We conducted searches in the following databases: MEDLINE (OVID), EMBASE (OVID), PsycINFO (OVID), CINAHL, the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), IEEEXplore ASSIAN, Google Scholar and the main Arabic databases Al Manhal, AskZad and Mandumah. We looked for studies that used apps in the self-management of hypertension from 2008–2016. We also checked the reference lists of the review papers and all the primary studies for additional references. Results: A total of 21 studies with a total of 3112 participants were included in the review. Of the 14 studies that assessed effectiveness of the apps in lowering BP, 10 studies (6 RCTs and 4 nonrandomised studies) reported that using the apps led to significant decreases in BP and seemed to be effective in the self-management of hypertension. Of these 10, only 2 RCTs and 3 nonrandomised studies had a low–moderate risk of bias. The results of this review are inconclusive regarding which combinations of functionalities would be most effective in lowering BP because of variation in the studies’ quality, but the data suggest that apps incorporating more comprehensive functionalities are likely to be more effective. In all the studies that assessed the usability of the apps and users’ acceptance of them, all the apps seemed to be accepted and easy to use. Conclusions: Most of the studies reported that apps might be effective in lowering BP and are accepted by users. Yet, the findings should be interpreted with caution, as most of the studies had a high risk of bias. More well-designed, large-scale studies are required to evaluate the real effect of using apps in lowering BP and to identify the most effective functionality combinations for lowering BP.