Provided herein are pharmaceutical compositions and formulations comprising mixed salts of gamma-hydroxybutyrate (GHB). Also provided herein are methods of making the pharmaceutical compositions and formulations, and methods of their use for the treatment of sleep disorders such as apnea, sleep time disturbances, narcolepsy, cataplexy, sleep paralysis, hypnagogic hallucination, sleep arousal, insomnia, and nocturnal myoclonus.