The atypical antipsychotic drugs (AAPDs) have markedly enhanced the treatment of schizophrenias but their use has been hindered by the major weight gain elicited by some AAPDs. We report that orexigenic AAPDs potently and selectively activate hypothalamic AMP-kinase, an action abolished in mice with deletion of histamine H1 receptors. These findings may afford a means of developing more effective therapeutic agents and provide insight into the hypothalamic regulation of food intake.