Supplementary Material for: Effectiveness of Intranasal Insulin for the Treatment of Olfactory Dysfunction: A Systematic Review

Introduction: To assess the effectiveness and safety of Intranasal Insulin (INI) for the treatment of Olfactory Dysfunction (OD) in patients with anosmia and/or hyposmia compared to placebo or no treatment.
Methods: We searched four databases: Medline, Scopus, Directory of Open Access Journals (DOAJ), and Springer Nature Journals. The study protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (ID: CRD42023456891). The protocol design was in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Participants with hyposmia or anosmia, aged 18 years or older, were included. Patients with an altered sense of smell due to anatomical malformations, trauma, neurodegenerative diseases, surgery, or intranasal lesions were excluded.
Results: Five studies that enrolled 131 participants were included. There were 131 participants, of whom 63 were male and 68 were female. The participants’ ages ranged from 16 to 56 years old. Almost all studies had a dose of 40 IU, but one study had different doses for different participants. Glycemic assessment was performed in three studies, which showed a very slight decrease in glucose, except in one study in which the drop in glucose reached 10.4 mg/dl. All studies agreed that there was an improvement in olfactory function after INI administration.
Conclusion: This systematic review concluded that INI can be an effective treatment option for patients with OD. However, conducting further well-designed clinical trials is highly recommended to establish robust clinical recommendations.