A water-dissolvable drug delivery device designed so as to reliably maintain a drug or active agent within a defined region against a mucosal surface. The drug delivery device comprises a water-dissolvable backing layer, an adhesive layer adjacent to at least a portion of the backing layer, and an active layer that is circumscribed by the backing layer and adhesive layer. The backing layer may optionally include a water-dissolvable hydrophilic region and a non-hydrophilic region at least partially encapsulated within the hydrophilic region that inhibits migration of water, drugs, or other active agents through the backing layer. The adhesive layer may be water-activated or it may have a peelable cover layer that, when removed, exposes the adhesive material. The active layer may comprise any drug or other active agent, either alone or in combination with (i) an enhancer that increases the ability of the drug or other active agent to diffuse through a mucosal membrane and/or (ii) a matrix material such as an alginate to hold the active layer together.