Provided herein are compositions comprising a dextromethorphan analog according to Formula I or Formula II or a pharmaceutically acceptable salt thereof of either of the foregoing, and a co-agent, e.g. , an antidepressant such as a serotonin norepinephrine reuptake inhibitor； a serotonin noradrenaline dopamine reuptake inhibitor； a norepinephrine dopamine reuptake inhibitor； a monoamine oxidase inhibitor； a selective serotonin reuptake inhibitor； and a tricyclic antidepressant or a pharmaceutically acceptable salt of any of the foregoing. The compositions are useful in the treatment of pseudobulbar affect, neuropathic pain, neurodegenerative diseases, brain injuries, and the like.
