Abstract: The invention relates to controlled release pharmaceutical compositions. These contain as active ingredient valproic acid, a salt of valproic acid, an ester of valproic acid, Valpromide, or any other pharmaceutically acceptable derivative of valproic acid which upon administration to humans provides a serum level of valproic acid, in combination with an additive which is selected from physiologically acceptable polymeric substances and from native proteins. The active ingredient is usually in the range of from 10 to 80 weight percent. The novel pharmaceutical compositions are prepared by applying a high pressure to a mixture of the ingredients. They result in a prolonged serum level of the active ingredient.