The invention relates to octahydro-pyrrolo[3,4-b]pyrrole N-oxides as prodrugs of CNS-active compounds, compositions comprising such compounds, methods for making the compounds, salts, and polymorphs, and methods of treating conditions and disorders using such compounds and compositions. Octahydro-pyrrolo[3,4-b]pyrrole N-oxides of formula (I) are prodrugs of histamine-3 antagonists, and are useful in treating conditions or disorders prevented by or ameliorated by histamine-3 receptor ligands. Octahydro-pyrrolo[3,4-b]pyrrole N-oxide compounds, methods for using such compounds, compositions for making them, and processes for preparing such compounds are disclosed herein.