306 Chapter 10 Results Our database literature searches yielded 331 results in total of which 191 were screened after the exclusion of duplicates (Figure 1A). After screening of the title and abstract, 31 full-text articles were reviewed. Seven original studies studying the possible effects of opioids on narcolepsy symptom severity were selected (Table 1). Three studies involved use of codeine, including two case reports [129, 131] and one report combining a case series, open label study and an RCT [130]. One conference presentation studied use of methadone [128], one case series involved tramadol [127], one case report included oxycodone and buprenorphine [126], and a postmortem study was found on the effects of morphine and heroin on hypocretin-producing neuron counts [125]. Figure 1. Study flow diagrams. (A) The PRISMA flow diagram of the systematic literature review [371]. (B) The recruitment flow diagram of the questionnaire and interview study. EDS = excessive daytime sleepiness; ICSD-3 = third edition of the International Classification of Sleep Disorders; NT1 = narcolepsy type 1; WHO ICTRP = World Health Organization International Clinical Trials Registry Platform.
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