COVID-19SMELLT2022NCT05539560
The Effect of Olfactory Training in Patients With COVID-19 Induced Olfactory Dysfunction
A study testing Olfactory training with essential oils and Olfactory training with fragrance-free oils in people with COVID-19, run by Ditte Gertz Mogensen at 1 site in Denmark.
Trial summary
Aim: The aim is to investigate the effect of olfactory training with essential oils versus olfactory training with placebo-oils in patients with COVID-19 induced olfactory dysfunction Study design: The study is a placebo-controlled randomized clinical trial with an intervention group and a control group. Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- COVID-19
- What is being tested?
- Olfactory training with essential oils and Olfactory training with fragrance-free oils
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 65 participants
- Where
- 1 siteDenmark
- Study dates
- 29 Jun 2022to 30 Sep 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Who may be able to join
- Olfactory dysfunction caused by COVID-19
- Hyposmia (16.25-30.5) or anosmia (<16) with or without parosmia assessed by TDI test with Sniffin Sticks performed in the Unit for Sense of Taste and Smell
- > 18 years of age
Who cannot join
- Cause of hyposmia, anosmia or parosmia other than COVID-19
- Does not read or speak Danish
- Lack of compliance to perform daily olfactory training
Trial locations and contacts
1 site in 1 country.
Denmark1 site, 1 recruiting
- Recruiting
Department of Otorhinolaryngology, Head and Neck Surgery & Audiology, Copenhagen University Hospital
Copenhagen, 2100
Ditte Gertz Mogensen, PhD-student, +45 35457508, ditte.gertz.mogensen@regionh.dk
Vibeke Backer, Professor, +45 3545 6033, nina.vibeke.backer@regionh.dk
About this study
Official title: The Effect of Olfactory Training in Patients With COVID-19 Induced Olfactory Dysfunction - A Randomized Placebo-controlled Clinical Trial
Aim: The aim is to investigate the effect of olfactory training with essential oils versus olfactory training with placebo-oils in patients with COVID-19 induced olfactory dysfunction
Study design: The study is a placebo-controlled randomized clinical trial with an intervention group and a control group. The intervention group receive four essential oils with scents of orange, lavender, clove, and peppermint. Patients in the control group receive a fragrance kit, consisting of the same containers, but with fragrance-free oils added. Both groups are instructed to smell each of the four oils for 30 seconds in the morning and evening, over a three-month intervention period. Patients are given a diary in which to record their olfactory training. The nurse or medical student instructing the patients in the training and performing the smell and taste tests is blinded.
Read more
Study population: Patients referred to the Unit for Sense of Taste and Smell in the Department of Otorhinolaryngology Head \& Neck and Audiology at Rigshospitalet.
Inclusion criteria:
- Impaired sense of taste and smell following COVID-19 > 3 months
- Hyposmia (16.25-30.5) or anosmia (<16) assessed by Sniffin' Sticks Olfactory Test for Threshold, Discrimination and Identification (TDI) performed in the Unit for Sense of Taste and Smell with or without parosmia based on medical history
- > 18 years of age
Exclusion criteria:
- Cause of hyposmia, anosmia or parosmia other than COVID-19
- Does not read or speak Danish
- Lack of compliance to perform daily olfactory training
Procedures:
- TDI-test: To assess patients' sense of smell, the TDI-test with Sniffin' Sticks is used, which is a validated tool with normative data.
Questionnaires:
- 'Taste and Smell Tool for Evaluation' is used to investigate quality of life related to impaired sense of taste and smell.
- Conditions
- COVID-19
- Being tested
- Olfactory training with essential oils, Olfactory training with fragrance-free oils
- Keywords
- Olfactory training, Quality of life, Olfactory dysfunction, Covid-19, Parosmia
- Medical subject headings
- COVID-19, Olfaction Disorders
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Olfactory training with essential oilsOther
Also called Urtegaarden ApS Essential Oils
Olfactory training twice daily with essential oils from Urtegaarden Aps with scents of orange, lavender, clove and peppermint. The olfactory training is performed every morning and evening, by smelling each of the oils for 30 seconds.
Olfactory training with fragrance-free oilsOther
Also called Urtegaarden ApS Essential Oils (Fragrance-free custom made)
Olfactory training twice daily with fragrance-free oils from Urtegaarden Aps in the same four containers as the intervention group. The olfactory training is performed every morning and evening, by smelling each of the oils for 30 seconds.
| Study group | Role | What they receive |
|---|---|---|
| Intervention group | Experimental | Olfactory training twice a day with essential oils Receives: Other: Olfactory training with essential oils |
| Control group | Placebo comparator | Olfactory training twice a day with fragrance-free oils Receives: Other: Olfactory training with fragrance-free oils |
What is being measured
The primary outcome is the main question the study is designed to answer.
Change in Extended Sniffin' Sticks Test score
Change in TDI score measured by Burghart Extended Sniffin' Sticks Test (TDI test). The TDI test, consists of a threshold test, a discrimination test, and an identification test. The results of the three subtests makes a total TDI score, where the minimum score is 1 and the maximum score is 48. A score >30 indicates normal olfactory function, a score between 15-30 indicates hyposmia and a score <15 indicates anosmia in the form of severely impaired or complete loss of olfaction.
Measured: 3 months follow-up
Secondary outcomes (1)
Change in Quality of Life
Change in Quality of Life measured by the questionnaire Taste and Smell Tool for Evaluation. The minimum score is 21 and the maximum score is 105. A higher score means worse outcome (quality of life).
Measured: 3 months follow-up
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted14 Sep 2022
- Study start29 Jun 2022
- Primary completion30 Apr 2024
- Study completion30 Sep 2025 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for COVID-19Studies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 65 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Ditte Gertz Mogensen
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor-investigator, Ditte Gertz Mogensen, Copenhagen University Hospital, Rigshospitalet
- Investigators
- Vibeke G Backer, Professor, Study chair, Copenhagen University Hospital, Rigshospitalet
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT05539560
- Sponsor's protocol ID
- 2022-ENT-1-olfactory
- Acronym
- SMELLT2022
- Status last verified
- Sep 2024
- First submitted
- 2 Sep 2022
- Last updated
- 23 Sep 2024
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
Publications
Mogensen DG, Aanaes K, Andersen IB, Jarden M, Backer V. Effect of Olfactory Training in COVID-19 Related Olfactory Dysfunction-A Placebo-Controlled Trial. Laryngoscope. 2025 Dec;135(12):4849-4857. doi: 10.1002/lary.32275. Epub 2025 May 15.
PubMed 40371997
Study at a glance
From the registry record, last updated by the sponsor on 23 Sep 2024. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- The Effect of Olfactory Training in Patients With COVID-19 Induced Olfactory Dysfunction - A Randomized Placebo-controlled Clinical Trial
- ClinicalTrials.gov ID
- NCT05539560
- Acronym / sponsor ID
- SMELLT2022 / 2022-ENT-1-olfactory
- Conditions
- COVID-19
- Keywords
- Olfactory training, Quality of life, Olfactory dysfunction, Covid-19, Parosmia
- Study type
- Interventional
- Recruitment status
- Unknown status
- Enrolment
- 65 participants (estimated)
- Lead sponsor
- Ditte Gertz MogensenUniversity, hospital or other
- Study start
- 29 Jun 2022 (actual)
- Primary completion
- 30 Apr 2024 (actual)
- Study completion
- 30 Sep 2025 (estimated)
- First posted
- 14 Sep 2022 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
Aim: The aim is to investigate the effect of olfactory training with essential oils versus olfactory training with placebo-oils in patients with COVID-19 induced olfactory dysfunction
Study design: The study is a placebo-controlled randomized clinical trial with an intervention group and a control group. The intervention group receive four essential oils with scents of orange, lavender, clove, and peppermint. Patients in the control group receive a fragrance kit, consisting of the same containers, but with fragrance-free oils added. Both groups are instructed to smell each of the four oils for 30 seconds in the morning and evening, over a three-month intervention period. Patients are given a diary in which to record their olfactory training. The nurse or medical student instructing the patients in the training and performing the smell and taste tests is blinded.
Study population: Patients referred to the Unit for Sense of Taste and Smell in the Department of Otorhinolaryngology Head \& Neck and Audiology at Rigshospitalet.
Inclusion criteria:
- Impaired sense of taste and smell following COVID-19 > 3 months
- Hyposmia (16.25-30.5) or anosmia (<16) assessed by Sniffin' Sticks Olfactory Test for Threshold, Discrimination and Identification (TDI) performed in the Unit for Sense of Taste and Smell with or without parosmia based on medical history
- > 18 years of age
Exclusion criteria:
- Cause of hyposmia, anosmia or parosmia other than COVID-19
- Does not read or speak Danish
- Lack of compliance to perform daily olfactory training
Procedures:
- TDI-test: To assess patients' sense of smell, the TDI-test with Sniffin' Sticks is used, which is a validated tool with normative data.
Questionnaires:
- 'Taste and Smell Tool for Evaluation' is used to investigate quality of life related to impaired sense of taste and smell.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| Intervention group | Experimental | Other: Olfactory training with essential oilsOlfactory training twice a day with essential oils |
| Control group | Placebo comparator | Other: Olfactory training with fragrance-free oilsOlfactory training twice a day with fragrance-free oils |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (3 listed)
- Olfactory dysfunction caused by COVID-19
- Hyposmia (16.25-30.5) or anosmia (<16) with or without parosmia assessed by TDI test with Sniffin Sticks performed in the Unit for Sense of Taste and Smell
- > 18 years of age
Key exclusion criteria (3 listed)
- Cause of hyposmia, anosmia or parosmia other than COVID-19
- Does not read or speak Danish
- Lack of compliance to perform daily olfactory training
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Olfactory training with essential oilsAlso: Urtegaarden ApS Essential OilsOlfactory training twice daily with essential oils from Urtegaarden Aps with scents of orange, lavender, clove and peppermint. The olfactory training is performed every morning and evening, by smelling each of the oils for 30 seconds. | Other | Intervention group |
| Olfactory training with fragrance-free oilsAlso: Urtegaarden ApS Essential Oils (Fragrance-free custom made)Olfactory training twice daily with fragrance-free oils from Urtegaarden Aps in the same four containers as the intervention group. The olfactory training is performed every morning and evening, by smelling each of the oils for 30 seconds. | Other | Control group |
Primary outcome
Change in Extended Sniffin' Sticks Test score
Time frame: 3 months follow-up
Change in TDI score measured by Burghart Extended Sniffin' Sticks Test (TDI test). The TDI test, consists of a threshold test, a discrimination test, and an identification test. The results of the three subtests makes a total TDI score, where the minimum score is 1 and the maximum score is 48. A score >30 indicates normal olfactory function, a score between 15-30 indicates hyposmia and a score <15 indicates anosmia in the form of severely impaired or complete loss of olfaction.
1 secondary outcome
Change in Quality of Life
Time frame: 3 months follow-up
Results and safety
Results are not available in the source record.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 23 Sep 2024.
- Derived from this study: PubMed 40371997Mogensen DG, Aanaes K, Andersen IB, Jarden M, Backer V. Effect of Olfactory Training in COVID-19 Related Olfactory Dysfunction-A Placebo-Controlled Trial. Laryngoscope. 2025 Dec;135(12):4849-4857. doi: 10.1002/lary.32275. Epub 2025 May 15.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Vibeke G Backer, Professor study chair
Copenhagen University Hospital, Rigshospitalet
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Olfactory training with essential oils and Olfactory training with fragrance-free oils in people with COVID-19, run by Ditte Gertz Mogensen at 1 site in Denmark.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 3 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: status not confirmed, as of the sponsor's last update on 23 Sep 2024. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Denmark. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
Results are not available in the source record.
How can a doctor refer a patient or contact the research team?
Contact Ditte G Gertz Mogensen, PhD-student (+45 35457508, ditte.gertz.mogensen@regionh.dk), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Change in Extended Sniffin' Sticks Test score (time frame: 3 months follow-up). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT05539560, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 23 Sep 2024; AzTrials last refreshed its copy on 7 Nov 2026.