COPANOS: use of gabapentin in the management of post-viral parosmia - a double-blind, randomised, placebo-controlled, multi-site trial - study protocol.

introductionParosmia is a qualitative olfactory disorder characterised by a distorted perception of smell, often experienced as unpleasant or offensive. Although parosmia has multiple aetiologies, post-viral parosmia has become increasingly prevalent following the COVID-19 pandemic. In the UK, post-viral parosmia affects an estimated 637 836 individuals and has a substantial negative impact on quality of life and mood. At present, there is no licensed or standardised treatment for this condition. Gabapentin, a gamma-aminobutyric acid analogue with neuromodulatory properties, has shown potential benefits at low doses in small, non-randomised studies; however, its efficacy requires further evaluation.

methodsUse of Gabapentin in the Management of Post-Viral Parosmia: A Double-Blind, Randomised, Placebo-Controlled, Multi-Site Trial (COPANOS) is a phase III, double-blind, randomised, placebo-controlled trial comparing gabapentin with placebo in adults aged 18-65 years with post-viral parosmia persisting for ≥6 months and <5 years. Participants will be randomised 1:1 to receive gabapentin, titrated to a maximum dose of 600 mg daily or a matching placebo for 8 weeks. The primary outcome is the between-group difference in mean parosmia severity scores at the end of treatment (week 8), measured using the parosmia domain of the validated Smell-Qx questionnaire. Secondary outcomes include quality of life (Smell- Qx), olfactory function assessed using the Sniffin' Sticks test battery, safety and tolerability and objective parosmia severity measured with the Sniffin' Sticks Parosmia Test (SSParoT). The trial will recruit 90 participants across two UK sites. ANALYSIS: The results will provide robust preliminary evidence on the efficacy and safety of low-dose gabapentin for managing post-viral parosmia and will inform the feasibility and design of targeted treatment guidelines. Defining effective treatment for post-viral parosmia is essential given the significant impact on patient well-being and the absence of current evidence-based interventions. ETHICS AND DISSEMINATION: The trial protocol has been reviewed and approved by Health Research Authority (HRA) and Health and Care Research Wales (HCRW): 25/WA/0298, 21/10/2025. Results will be analysed and published as soon as possible following trial completion. Findings will be summarised on the study webpage and shared with trial participants in plain English. Trial results will also be uploaded to relevant trial registries within 12 months of trial completion. The Rosetrees Trust will be acknowledged in all publications. Publications will follow International Committee of Medical Journal Editors authorship guidelines, and professional medical writers will not be used. TRIAL REGISTRATION NUMBER: ISRCTN82171427, IRAS 1012783.