Embodiments of the invention describe compositions and methods for the administration of fast disintegrating atypical antipsychotics, metabolites of atypical antipsychotics, and antidepressants which reduce weight in patients previously taking conventional formulation of atypical antipsychotics and antidepressants. In a preferred embodiment said fast dissolving atypical antipsychotic is FAZACLO. In another preferred embodiment said fast dissolving metabolite of an atypical antipsychotic is desmethyl clozapine. In another preferred embodiment said fast dissolving antidepressant is paroxetine.