An interventional study of Nasal Insert + VNS and Nasal Insert in Hyposmia, sponsored by Karolinska Institutet. Active, not recruiting at 1 site in Sweden. Open to participants aged 18 Years to 65 Years. Per ClinicalTrials.gov, last updated 2025-08-27.
Sponsored by Karolinska Institutet · Not applicable, Interventional, and Treatment
Hyposmia, a reduced sense of smell, is commonly linked to viral infections like COVID-19. Currently, the sole recommended treatment is olfactory training, a method that is both time-intensive and limited in its effectiveness. Our team has previously evaluated a new type of olfactory training using nasal inserts that show increased adherence to training (compared to standard olfactory training using common household odors) but with similar treatment effect. The investigators recently demonstrated that brief transcutaneous vagus nerve stimulation (VNS) in the cymba conchae region affected participants olfactory abilities but only when a stimulation frequency relevant to olfactory bulb processing frequencies was used. The notion that VNS might modulate olfactory functions stems from findings in rats where VNS of the cervical nerve inhibited neurons within the periglomerular layers of the olfactory bulb. Although there is no known monosynaptic connection between the vagus nerve and the olfactory system in humans, VNS activates areas with mono-synaptic connections to the olfactory bulb, such as amygdala, hippocampus, and the hypothalamus. Given that VNS modulates the olfactory bulb in rats and our treatment protocol modulate olfactory functions in humans, the investigators hypothesize that VNS, when paired with olfactory training, will enhance olfactory functions in patients with hyposmia.
Participants with hyposmia will be recruited and randomly assigned to one of two treatment groups. One group will engage in olfactory training using nasal inserts while the other will use olfactory training with nasal inserts along with VNS. Both interventions will take place at home, Monday through Friday, over a two-month period. To evaluate the outcomes, subjective and objective measures of olfactory function will be collected before, during, and after the treatment, along with assessments of quality of life and overall well-being. Treatment adherence will also be evaluated at the end of treatment.
180 studies on the registry are indexed under Anosmia; 45 are open to participants now.
This study's planned enrollment of 40 is below the median of 60 across 114 interventional studies indexed under Anosmia.
Browse Anosmia studies →Karolinska Institutet is the lead sponsor of 1,148 studies on the registry; 276 are open to participants now.
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Exclusion Criteria:
Participants will complete olfactory training with scented nose plugs along with VNS
Other: Nasal Insert + VNS
Participants will complete olfactory training with scented nose plugs
Other: Nasal Insert
Participants will complete olfactory training with scented nose plugs along with VNS
Participants will complete olfactory training with scented nose plugs
Sniffin' Sticks TDI test (objective olfactory function)
Objective olfactory function will be measured using the Sniffin' Sticks TDI extended test (Burghart Messtechnik) which gives separate scores for odor threshold, odor discrimination, and odor identification; as well as a summated score (TDI) of objective olfactory function.
Time frame: From enrollment to the end of treatment at 8 weeks
Self rated olfaction questionnaire (subjective olfactory function)
Does the use of VNS increase the effect of olfactory training on subjective qualitative (parosmia) and quantitative (hyposmia) symptoms compared to only olfactory training? For this outcome, we will use self-ratings of qualitative and quantitative olfactory function, for example "Do you experience smell distortion (parosmia)?" (if yes, rate your problem from 0 to 10) and "rate your sense of smell from 0 to 10"
Time frame: From enrollment to the end of treatment at 8 weeks
General Wellbeing Questionnaire (general wellbeing)
Does the use of VNS increase the effect of olfactory training on subjective general wellbeing compared to only olfactory training? For this outcome, we will use the General Wellbeing Questionnaire (GWB).
Time frame: From enrollment to the end of treatment at 8 weeks
Adherence to training questionnaire (Compliance)
Does the use of VNS affect the compliance of olfactory training compared to olfactory training only? For this outcome, we will use a questionnaire that participants answer during their final visit. The questionnaire separately assesses consistency, perceived tediousness, forgetfulness, and cause for potential discontinuation of the training, for example by asking "how many times did you forget your training?"
Time frame: From enrollment to the end of treatment at 8 weeks
Plan to share: Yes — anonymized data
No publications or documents are linked to this record.
Started Mar 2025 (actual). Primary completion is estimated for May 2026, 14 months after the start.
Of 50 non-industry interventional studies with no phase under Anosmia, half reached primary completion within 28 months of starting (the median), counting those still running; a quarter within 14 and three quarters within 37. This study's planned 14 months is below that.
Counting every sponsor, half of 50 studies reached it within 28 months; a quarter within 14 and three quarters within 37.
How these figures are worked out, and which studies are left out of them.
This study is active, not recruiting, as verified in Aug 2025. You cannot join it, but the record below documents what was studied.
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