A granule including a solid core on which is supported an active ingredient, said active ingredient being selected from gamma-hydroxybutric acid or one of its pharmaceutically acceptable salts, said granule further including, supported on said solid core, one or more compounds which may generate gas evolvement, one or more diluents, said granule being in that it is coated with a membrane, and in that the solid core represents from 15% to 50% by weight based on the total weight of the granule.