Abnormally low levels of acylcarnitine have been observed in patients with narcolepsy.[48] These same low levels have been associated with primary hypersomnia in general in mouse studies. "Mice with systemic carnitine deficiency exhibit a higher frequency of fragmented wakefulness and rapid eye movement (REM) sleep, and reduced locomotor activity." Administration of acetyl-L-carnitine was shown to improve these symptoms in mice.[49] A subsequent human trial found that narcolepsy patients given L-carnitine spent less total time in daytime sleep than patients who were given placebo.[50]