Dextromethorphan has been found to have neuroprotective effects and is being studied for the treatment of amyotrophic lateral sclerosis (ALS). Dexpramipexole reduces mitochondrial reactive oxygen species (ROS) production, inhibits the activation of apoptosis pathways, and improves cell survival in response to various neurotoxins and β-amyloid neurotoxicity. Compared with the S-(-) isomer, dextromethorphan has lower dopamine agonist activity.