This article critically examines the ways in which the disruptive capabilities of generative AI have propitiated and fostered a synthetic public opinion. This synthetic public opinion is characterised by the breakdown of communicative action, the datafication of opinions, the monopolisation of the public sphere, information intoxication, mass social surveillance, the predominance of synthetic and artificial content over real content, and the difficulty of differentiating synthetic content from real content. The objective of this article is to examine the emergence and emergency of the synthetification of public opinion in democracies of the European Union with a view to determining the most appropriate courses of action to address the negative impacts of this phenomenon. In order to achieve this purpose, firstly, the situation of artificialisation of public opinion prior to the irruption of the most sophisticated generative AI is presented. Secondly, the changes produced by the irruption of generative AI in the public sphere and in public opinion are examined in depth. Thirdly, it analyses the main negative impacts of the synthetification of public opinion on the proper functioning of democratic systems. Finally, a number of potential courses of action are proposed with the aim of strengthening the fundamental pillars of the deliberative democracies of the European Union in the face of the impacts of synthetification.