This invention relates to the use of a ligand of the 5-HT4 receptor or of a pharmaceutically acceptable salt of this ligand and to a nucleic acid coding for a 5-HT4 receptor or of a functionally equivalent receptor for a drug for treating and/or preventing a pathology associated with an obsessional behavior such as anorexia, bulimia and the addiction to drugs of abuse or obesity. The invention also relates to a method for identifying a compound that is biologically active in the treatment and/or the prevention of a pathology associated with an obsessional conduct or obesity including: a) placing the 5-HT4 receptor or a functionally equivalent receptor in contact with this biologically active compound, and b) the determination of whether this biologically active compound is capable of modulating the basal activity of the 5-HT4 receptor or of a functionally equivalent receptor.