An adhesive for medical patches or for transdermal therapeutic systems which contains a component or a combination of at least two components, such as (a) polyvinyl alcohols, (b) cellulose derivatives, (c) polyethers, (d) acid anhydrides and their acids and salts, as well as (e) non-pressure-sensitive adhesive polyacrylates. The adhesive has a tackiness which is activated and/or increased by contact with moisture or by absorption of moisture.