The present invention is directed to immediate release film coating systems for use on oral dosage forms such as compressed tablets and other orally-ingestible substrates which have improved moisture barrier properties. The film coating systems can be applied either directly to a substrate or after the substrate has been coated with a subcoat. In preferred aspects, the moisture barrier film coating is prepared as a dry powder mixture containing polyvinyl alcohol, a polymer with pH dependent solubility, a plasticizer, a glidant, and, optionally, a detackifier, an alkalizing agent and a pigment. Film coating compositions containing an aqueous suspension of the powder mixtures, methods of applying the coatings to substrates and the coated substrates are also disclosed.