Demadex is used to treat high blood pressure or water retention in adults. Although Demadex cannot cure these conditions, it can help to lower blood volume by increasing the amount of water and salt the kidneys remove from the blood. As a result, this can help to decrease the risk of developing health problems associated with high blood pressure, such as heart disease and congestive heart failure. At this time, there are no universally accepted off-label Demadex uses.