Disclosed herein are polymorphic and amorphous forms of anhydrate, hydrate, and solvates of (R)-2-hydroxy-2-methyl-4-(2,4,5-trimethyl-3,6-dioxocyclohexa-1,4-dienyl)butanamide and methods of using such compositions for treating or suppressing oxidative stress disorders, including mitochondrial disorders, impaired energy processing disorders, neurodegenerative diseases and diseases of aging. Further disclosed are methods of making such polymorphic and amorphous forms.