NCT04764981.

Study name	Olfactory training for olfactory dysfunction after coronavirus disease ‐ 19 (COVID‐19)
Methods	Two‐arm, unblinded, single‐centre, parallel‐group RCT with 3 months duration of treatment and follow‐up NB trial registry states double‐blinded, but no intervention used in comparator group, therefore must be unblinded to participants
Participants	Individuals with persistent olfactory dysfunction following COVID‐19; duration of dysfunction unclear Inclusion criteria: Confirmed diagnosis of COVID‐19 by real time polymerase chain‐reaction for SARS‐CoV‐2 or serological tests for SARS‐CoV‐2 antigens Olfactory dysfunction confirmed by Connecticut Chemosensory Clinical Research Test (CCCRC‐T) Exclusion criteria: Smokers Individuals with diagnosed rhinitis Individuals with diagnosed neurological diseases Individuals undergoing brain surgery Previous history of hyposmia and/or anosmia Pregnancy Allergy to any of the substances present in the olfactory test kit Individuals who are undergoing another treatment for olfactory dysfunction Estimated sample size: 300 participants (additional 50 healthy controls will be recruited for a separate study arm)
Interventions	Intervention group: Olfactory training: 4 odours (rose, eucalyptus, lemon and cloves), twice daily training for 30 seconds per odour for a total of 3 months Control group: No intervention
Outcomes	Outcomes of interest in the review: Primary outcomes: Presence of normal sense of smell CCCRT olfactory test will be used to assess olfactory function, and classify individuals as having normosmia Serious adverse effects Not reported Change in sense of smell CCCRT olfactory test will be used to assess olfactory function. An olfactory function score (0 = worst score, 7 = best score) will also be assessed. It is unclear whether these will be reported as dichotomous or continuous outcomes. Secondary outcomes: Prevalence of parosmia Not reported Change in sense of taste Not reported Disease‐related quality of life Not reported Other adverse effects (including nosebleeds/bloody discharge) Not reported Other outcomes reported by the study: MRI of the olfactory bulb
Starting date	May 2021
Contact information	Alna Carolina Mendes Parahnos, no contact details provided
Notes	Registered in Brazil  Estimated study completion date 1 May 2024 It is unclear if participants will have had symptoms for < 4 weeks at baseline, therefore this study may not be suitable for inclusion in this review. Further details will be obtained when the trial is published.