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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:
Exclusion criteria:
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.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Intervention group | Experimental | Olfactory training twice a day with essential oils |
|
| Control group | Placebo Comparator | Olfactory training twice a day with fragrance-free oils |
|
| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Olfactory training with essential oils | Other | 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. |
| Measure | Description | Time Frame |
|---|---|---|
| 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. | 3 months follow-up |
| Measure | Description | Time Frame |
|---|---|---|
| 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). | 3 months follow-up |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Ditte G Gertz Mogensen, PhD-student | Contact | +45 35457508 | ditte.gertz.mogensen@regionh.dk | |
| Vibeke Backer, Professor | Contact | +45 35456033 | nina.vibeke.backer@regionh.dk |
| Name | Affiliation | Role |
|---|---|---|
| Vibeke G Backer, Professor | Rigshospitalet, Denmark | Study Chair |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Department of Otorhinolaryngology, Head and Neck Surgery & Audiology, Copenhagen University Hospital | Recruiting | Copenhagen | 2100 | Denmark |
| PubMed Identifier | Type | Citation | Retractions |
|---|---|---|---|
| 40371997 | Derived | 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. |
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| Type | Includes Protocol | Includes SAP | Includes ICF | Document Label | Document Date | Document Uploaded Date | Document File Name |
|---|---|---|---|---|---|---|---|
| Prot_SAP_ICF | Yes | Yes | Yes | Study Protocol, Statistical Analysis Plan, and Informed Consent Form | Sep 2, 2022 | Sep 9, 2022 | Prot_SAP_ICF_000.pdf |
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| ID | Term |
|---|---|
| D000086382 | COVID-19 |
| D000857 | Olfaction Disorders |
| ID | Term |
|---|---|
| D011024 | Pneumonia, Viral |
| D011014 | Pneumonia |
| D012141 | Respiratory Tract Infections |
| D007239 | Infections |
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| ID | Term |
|---|---|
| D000094562 | Olfactory Training |
| D009822 | Oils, Volatile |
| ID | Term |
|---|---|
| D013812 | Therapeutics |
| D009821 | Oils |
| D008055 | Lipids |
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|
|
| Olfactory training with fragrance-free oils | Other | 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. |
|
|
| D014777 |
| Virus Diseases |
| D018352 | Coronavirus Infections |
| D003333 | Coronaviridae Infections |
| D030341 | Nidovirales Infections |
| D012327 | RNA Virus Infections |
| D008171 | Lung Diseases |
| D012140 | Respiratory Tract Diseases |
| D012678 | Sensation Disorders |
| D009461 | Neurologic Manifestations |
| D009422 | Nervous System Diseases |
| D012816 | Signs and Symptoms |
| D013568 | Pathological Conditions, Signs and Symptoms |