A Phase 2/3 interventional study of Trigeminal Nerve Stimulation (TNS) and Active Smell Training (ST) in Smell Dysfunction, Olfactory Disorder and Long COVID, sponsored by Medical University of South Carolina. Recruiting at 1 site in United States. Open to participants aged 18 Years to 65 Years. Per ClinicalTrials.gov, last updated 2026-04-02.
Sponsored by Medical University of South Carolina · Phase 2/3, Interventional, and Treatment
Persistent smell loss that can include diminished or distorted smell function is a common symptom of long COVID syndrome. There are limited treatment options for long COVID-related smell loss. This study aims to determine the efficacy of two at-home treatments, smell training and non-invasive trigeminal nerve stimulation. This study requires participants to conduct daily at-home treatment sessions, attend three in-person study visits at the MUSC Department of Psychiatry and Behavioral Sciences, and complete electronic questionnaires over the 12-week trial, and again at the six-month timepoint. Participants in this trial may benefit directly with an improvement in sense of smell. However, participation may also help society more generally, as this study will provide new information about long COVID-related smell loss and its treatment.
Sudden smell loss (SL), a hallmark feature of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-coV-2/COVID), frequently persists well past the initial recovery; rates of unresolved anosmia (total loss) are 21%, with unresolved hyposmia (reduced smell) or parosmia (distorted smell) higher at nearly 50%. SL is now recognized as a core symptom of "long COVID" (LC), which also includes other impairments in mood, cognition, and sleep. Given that SL itself can negatively impact many of the same problems being recognized in the symptomatology of LC, it is likely that SL is both a symptom of LC and a contributing factor that worsens other LC symptoms (i.e. mood, cognition, sleep, etc.). As such, successful treatment of SL could also help to improve these other LC symptoms.
Smell/olfactory training (ST) is currently being studied as a treatment for COVID-related SL. Classic ST requires twice daily practice of sniffing odorants over the course of 3 months to regenerate olfactory neurons, engage smell-related cognitive functions, and retrain the brain to smell. ST is promising as a stand-alone treatment. However, its limitations include the burden of many months of daily practice that often leads to sub-optimal compliance and dropout.
The current study aims to determine whether the benefits of ST can be accelerated and enhanced by using a novel, adjunct neuromodulatory intervention to conventional ST. Trigeminal nerve stimulation (TNS) is a non-invasive, pain-free, method of neuromodulation that delivers low levels of electrical stimulation to the trigeminal circuit, having potential to enhance smell function through activation of the highly connected olfactory-intranasal trigeminal systems. Prior work demonstrated TNS-enhanced psychophysical detection of odorants. Yet the effects of TNS are extensive, i.e. improved executive functioning (e.g. attention), sleep quality, and daytime sleepiness, as well as therapeutic efficacy across a number of neuropsychiatric disorders. Thus, TNS-as an adjunct to ST-may not only improve overall efficacy and speed of recovery of SL, but may help to treat some of the other symptoms of LC that ST, and improvement in smell function, may not fully resolve.
This randomized, controlled trial (RCT) of ST and combination TNS and ST in adults with COVID-related SL will use a 3- group design: Group 1) Active ST (N=60), Group 2) Placebo ST (PBO, N=60), and Group 3) Active TNS plus Active ST (N=60). Our primary objectives are to 1) determine the efficacy of ST versus potential natural gains in function, 2) determine the TNS-enhanced effects of ST on SL, and 3) determine whether TNS+ST is more efficacious than ST in treating the other symptoms of LC.
180 studies on the registry are indexed under Anosmia; 45 are open to participants now.
This study's planned enrollment of 145 is above the median of 60 across 114 interventional studies indexed under Anosmia.
Browse Anosmia studies →Medical University of South Carolina is the lead sponsor of 874 studies on the registry; 166 are open to participants now.
Of its 131 completed or terminated interventional studies of FDA-regulated products, 104 (79%) have results posted.
Compared within Anosmia, this study's primary condition as ClinicalTrials.gg classifies it; the registry's first condition term is Olfaction Disorders. The counts are of registry records indexed under each term, refreshed daily. How we classify →
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
30 minutes of once/day TNS and twice/day ST conducted 5 days/week for 12 weeks and a total of 60 stimulation and 120 smell training sessions
Device: Trigeminal Nerve Stimulation (TNS) · Other: Active Smell Training (ST)
5 minutes of daily ST conducted twice/day, 5 days/week for 12 weeks and a total of 120 training session
Other: Active Smell Training (ST)
5 minutes of daily PBO conducted twice/day, 5 days/week for 12 weeks and a total of 120 training sessions
Other: Placebo Smell Training (PBO)
Non-invasive, pain-free, low-level electrical stimulation to the forehead to modulate the trigeminal nerve and enhance smell function through activation of the highly connected olfactory-intranasal trigeminal brain circuits.
Also known as: Transcutaneous Electrical Nerve Stimulation
Sniffing various higher intensity odorant chemicals while performing odor-related cognitive tasks. 16 odorant chemicals will be used for training including: 2 phenyl ethanol, eugenol, lemon, eucalyptus, cinnamon, peppermint, coffee, mandarin, lavender, vanilla, lilac, ginger, chocolate, thyme, banana, and bacon.
Also known as: Olfactory Training
Sniffing the same lower intensity odorant chemicals (i.e. N-butanol and 2-phenyl ethanol) over the course of the trial and performing no odor-related cognitive tasks.
Change in Psychophysical Olfactory Function from Baseline to 4 and 12 Weeks
Sniffin' Sticks (Bughardt Messtechnik, Wedel Germany) will be used to determine odor threshold (T), odor discrimination (D), and odor identification (I), each on 16-point scales, and summed for a total TDI score. Higher scores indicate better function.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Perceived Intensity of Odorants from Baseline to 4 and 12 Weeks
Perceived intensity on 100-mm visual analog scales with anchor points: 0="imperceptible" to 100="extremely intense" will be rated for suprathreshold concentrations of PEA, vanilla, eugenol, and eucalyptus.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Perceived Hedonics of Odorants from Baseline to 4 and 12 Weeks
Perceived hedonics on 100-mm visual analog scales with anchor points: 0="extremely unpleasant" to 100="extremely pleasant".
Time frame: 2 times: 4 weeks, 12 weeks
Change in Olfactory-related Quality of Life from Baseline to 4 and 12 Weeks
The Modified Questionnaire of Olfactory Disorders-Negative Statements (QOD-NS) consists of 17 negative statements (rated on a scale from 0 to 3; total score ranging from 0 to 51), with lower scores indicating better olfactory-related quality of life.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Impact of Olfactory Loss from Baseline to 4 and 12 Weeks
The Impact of Olfactory Loss Visual Analog Scale (IOL-VAS) consists of 9 separate items assessing the impact of olfactory loss upon mood, food enjoyment, social interactions, safety, hygiene, sex, cooking, appetite, and weight changes, rated from 0 (no impact) to 10 (biggest impact possible).
Time frame: 2 times: 4 weeks, 12 weeks
Change in Long COVID Symptoms from Baseline to 4 and 12 Weeks
53 long COVID symptoms (scored from 0-53 reflecting the number of different symptoms experienced) and the impact of those symptoms (scored from 0=no impact to 10=maximal impact) will be obtained.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Sustained Attention from Baseline to 4 and 12 Weeks
The Sustained Attention to Response Task (SART) is a computer-based go/no-go task that requires participants to withhold behavioral response to a single, infrequent target (often the digit 3) presented amongst a background of frequent non-targets (0-2, 4-9).
Time frame: 2 times: 4 weeks, 12 weeks
Change in Cognitive Function from Baseline to 4 and 12 Weeks
The NIH Toolbox Cognitive Battery is a widely used assessment for detecting cognitive impairment. This test assesses short-term memory, executable performance, attention, and focus.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Mood State from Baseline to 4 and 12 Weeks
The Profile of Mood States Short Form (POMS-SF) is a psychological rating scale used to assess transient, distinct mood states across six different dimensions including Tension or Anxiety, Anger or Hostility, Vigor or Activity, Fatigue or Inertia, Depression or Dejection, and Confusion or Bewilderment.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Sleep Quality from Baseline to 4 and 12 Weeks
The Pittsburgh Sleep Quality Index (PSQI) is a self-report questionnaire that assesses sleep quality over a 1-month time interval. The measure consists of 19 individual items, creating 7 components that produce one global score. Scores greater than 5 are indicative of a sleep disturbance.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Excessive Daytime Sleepiness from Baseline to 4 and 12 Weeks
The Epworth Sleepiness Scale (ESS) is a measure intended to assess daytime sleepiness. Items consist of 8 different activities which are rated according to how likely it would be to doze off or fall asleep if engaged in that activity. A score of 10 or more is indicative excessive daytime sleepiness.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Symptoms of Depression from Baseline to 4 and 12 Weeks
The Patient Health Questionnaire-9 (PHQ-9) is a self-administered 9-item questionnaire to screen for the presence and severity of depression. Items are rated on a 3pt scale ranging from 0="Not at all" to 3="Nearly every day". Total score ranges from 0-27 and is used to classify depression severity: 0-4=None/Minimal; 5-9=Mild; 10-14=Moderate; 15-19=Moderately Severe; 20-27=Severe.
Time frame: 2 times: 4 weeks, 12 weeks
Change in Symptoms of Anxiety from Baseline to 4 and 12 Weeks
The Generalized Anxiety Disorder-7 (GAD-7) is a 7-item questionnaire to screen for presence and severity of anxiety disorder. Items are rated on a 3pt scale ranging from 0="Not at all" to 3="Nearly every day". Total score ranges from 0 to 21 and is used to classify anxiety severity: 0-4 (minimal anxiety), 5-9 (mild anxiety), 10-14 (moderate anxiety), 15-21 (severe anxiety).
Time frame: 2 times: 4 weeks, 12 weeks
Treatment Feasibility, Acceptability, and Fidelity at 4 and 12 weeks
Quantitative measurements will include the number of 1) sessions completed (completion rate), 2) technical problems, 3) adverse events, 4) study drop-out, and 5) the number of study-issued treatment cases returned at the end of treatment. The Feasibility of Intervention Measure (FIM) and the Acceptability of Intervention Measure (AIM) will be used. Both the FIM and AIM contain 4 items that are scored on a 5-point scale (1=completely disagree to 5=completely agree). Responses are averaged across the 4 items, with a score of 4 or more indicating adequate feasibility and acceptability of an intervention. Fidelity (i.e. adherence) that the treatment is delivered as intended will be measured by study staff who will rate adherence on a 5-point scale (1=little to 5=complete). Qualitative data using open-ended questions regarding the nature of any technical problems and the reasons for missed treatment sessions will be assessed.
Time frame: 2 times: 4 weeks, 12 weeks
Durability of Treatment on Subjective Olfactory Function at the 6-month Follow Up
Subjective function will be assessed with the QOD-NS and IOL-VAS.
Time frame: 1 time: 6 months
Durability of Treatment on Long COVID Symptoms at the 6-month Follow Up
53 long COVID symptoms (scored from 0-53 reflecting the number of different symptoms experienced) and the impact of those symptoms (scored from 0=no impact to 10=maximal impact) will be obtained.
Time frame: 1 time: 6 months
Durability of Treatment on Mood at the 6-month Follow Up
Mood will be assessed with the PHQ-9, GAD-7, and POMS-SF
Time frame: 1 time: 6 months
Durability of Treatment on Sleepiness and Sleep Quality at the 6-month Follow Up
Sleepiness and Sleep Quality will be assessed with the ESS and PSQI
Time frame: 1 time: 6 months
Plan to share: Yes — Original data (de-identified) will be available to other researchers upon request. Human subjects' rights to privacy will be protected and the identity of human subjects will not be revealed with any request.
Supporting information: Study protocol
Time frame: IPD will be shared after the primary data analyses are complete and our final findings are published.
Access criteria: Information on where the data will be available and how to access it will be published with all publications/presentations that come from this study
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