A water-soluble film having a thickness of from 0.05 mm to 0.3 mm, comprising at least one biologically active substance and/or at least one therapeutically active substance and, as a film-forming agent, an alginate salt of monovalent cation or a mixture of alginate salts of monovalent cation, the film-forming agent being such that a 10% aqueous solution thereof at a temperature of 20°C has a viscosity of 100-1000 mPas, as measured at a shear rate of 20 rpm by use of a Brookfield viscometer with a spindle No. 2. A method of preparing the film. The film is useful for delivery of active ingredients to a mammal.
