Treatment of Postviral Olfactory Dysfunction

A decreased sense of smell (hyposmia) is often caused by viral infections, such as COVID-19. Today, the only recommended treatment for hyposmia is olfactory training, a time consuming method with limitations in terms of both compliance and effect. The aim of this study is therefore to evaluate, as well as optimize, a new treatment method for olfactory loss.

Hyposmic participants will be recruited and randomized into two different treatment conditions. One group will do regular olfactory training and the other will do passive olfactory training with scented nose plugs. The training will be conducted in the home of the individual monday through friday for two consecutive months. Subjective and objectvie measures of olfactory problems will be assessed before and after treatment, as well as subjective measures related to quality of live and genereal wellbeing.

Study Overview

• Status: Completed
• Conditions: Hyposmia
• Intervention / Treatment: Device: Nose plug; Other: Regular olfactory training

• Study Type: Interventional
• Enrollment (Actual): 120
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Sweden
  • Stockholm County
    • Solna, Stockholm County, Sweden, 17177
      • Karolinska Institutet

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• 18 - 65 years old
• Physically and cognitively capable of participating in the study
• Having appropriate olfactory screening test scores (hyposmic)

Exclusion Criteria:

• Anosmics
• Individuals with other diagnoses that could affect the study results

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Olfactory training with nose plugs; Participants will complete olfactory training with scented nose plugs.	Device: Nose plug; Participants will complete olfactory training with scented nose plugs.
Active Comparator: Olfactory training with household odors; Participants will complete olfactory training with odors found in their household.	Other: Regular olfactory training; Participants will complete olfactory training with regular odors found in their home.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Objective olfactory function	Does the use of scented nose plugs increase the effect of olfactory training on objective olfactory function compared to regular olfactory training? For this outcome, we will use the standardized Sniffin' Sticks test to assess olfactory function.	2 months
Subjective symptoms and social/emotional consequences	Does the use of scented nose plugs increase the effect of olfactory training on subjective symptoms and social/emotional consequences compared to regular olfactory training? For this outcome, we will use the Sino-Nasal Outcome Test (SNOT).	2 months
Subjective health	Does the use of scented nose plugs increase the effect of olfactory training on subjective health compared to regular olfactory training? For this outcome, we will use the Self-Rated Health 5 measure and SF-36.	2 months
Subjective olfactory function	Does the use of scented nose plugs increase the effect of olfactory training on subjective olfactory function compared to regular olfactory training? For this outcome, we will use the Self-Reported Mini Olfactory Questionnaire.	2 months
Subjective degree of suffering from olfactory impairment	Does the use of scented nose plugs increase the effect of olfactory training on subjective degree of suffering from olfactory impairment compared to regular olfactory training? For this outcome, we will use the Questionnaire of Olfactory Disorders - Negative Statements.	2 months
Subjective parosmia	Does the use of scented nose plugs increase the effect of olfactory training on subjective parosmia compared to regular olfactory training? For this outcome, we will use the Landis parosmia questionnaire.	2 months
Subjective depressive symptoms	Does the use of scented nose plugs increase the effect of olfactory training on depressive symptoms compared to regular olfactory training? For this outcome, we will use the Beck Depression Inventory (BDI).	2 months
Subjective general wellbeing	Does the use of scented nose plugs increase the effect of olfactory training on depressive symptoms compared to regular olfactory training? For this outcome, we will use the General Well Being Schedule.	2 months
Compliance	Does the use of scented nose plugs increase the compliance of olfactory training compared to regular olfactory training? For this outcome, we will use questions asking the participants about their experience during the olfactory training, specifically targeting their compliance, such as how often they actually completed the olfactory training and how often they forgot to.	2 months

Collaborators and Investigators

• Sponsor: Karolinska Institutet
• Collaborators: Region Skane
• Investigators: Principal Investigator: Johan N Lundstrom, Karolinska Institutet

Publications and helpful links

General Publications

• Winter AL, Henecke S, Thunell E, Swartz M, Martinsen J, Sahlstrand Johnson P, Lundstrom JN. Olfactory training using nasal inserts is more effective due to increased adherence. Rhinology. 2025 Aug 1;63(4):477-485. doi: 10.4193/Rhin24.369.

Study record dates

Study Major Dates

• Study Start (Actual): October 17, 2023
• Primary Completion (Actual): June 21, 2024
• Study Completion (Actual): July 1, 2025

Study Registration Dates

• First Submitted: November 8, 2023
• First Submitted That Met QC Criteria: November 16, 2023
• First Posted (Actual): November 21, 2023

Study Record Updates

• Last Update Posted (Estimated): September 3, 2025
• Last Update Submitted That Met QC Criteria: August 26, 2025
• Last Verified: August 1, 2025

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Neurologic Manifestations; Nervous System Diseases; Sensation Disorders; Olfaction Disorders; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Anosmia
• Other Study ID Numbers: 2023-03779-01; 2021-06527 (Other Grant/Funding Number: Swedish Research Foundation)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No