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

The aim of the study was 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.

We searched four databases: Medline, Scopus, Directory of Open Access Journals (DOAJ), and Springer Nature. The study protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (ID: CRD42023456891). The protocol design was in accordance with the PRISMA. Participants with hyposmia or anosmia aged ≥18 years were included. Patients with an altered sense of smell due to anatomical malformations, trauma, neurodegenerative diseases, surgery, or intranasal lesions were excluded from the study.

Five studies with 131 participants were included. There were 131 participants, of whom 63 were men and 68 were women. The participants' ages ranged from 16 to 56 years. Almost all studies used a dose of 40 IU, except one that used 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 olfactory function improved after INI administration.

This systematic review concluded that INI can be an effective treatment option for patients with OD. However, further well-designed clinical trials are required to establish robust clinical recommendations.