http://www.hypersomniafoundation.org/how-long-does-it-take-for-sodium-oxybate-to-work/
Background
According to the Narcolepsy Network, although it affects more than 200,000 people in the US, narcolepsy is estimated to be undiagnosed or untreated in 75% of people with the disorder. This lack of recognition leads to delays in effective treatment and decreased quality of life. The US Food and Drug Administration has approved a variety of drugs to treat narcolepsy-associated excessive daytime sleepiness (EDS), including modafinil (Provigil), armodafinil (Nuvigil), methylphenidate, and amphetamine. Sodium oxybate (Xyrem) has been approved to treat the EDS and cataplexy associated with narcolepsy.