Coenzyme Q10 in Hearing Disorders: Replacement Therapy in Mitochondrial Deafness and Neuroprotective Use in Acquired Hearing Loss

Background/Objectives: Coenzyme Q10 (CoQ10) is crucial for mitochondrial bioenergetics and redox balance and has been studied in hearing disorders. Its clinical use ranges from genetic mitochondrial deafness to acquired hearing loss associated with oxidative stress. This review aimed to map human clinical evidence on CoQ10 in hearing issues and differentiate its therapeutic roles based on underlying causes. Methods: This review was conducted following the PRISMA Extension for Scoping Reviews (PRISMA-ScR). A systematic search of PubMed, Europe PubMed Central, the Directory of Open Access Journals (DOAJ), and ClinicalTrials.gov was performed. Human clinical studies evaluating CoQ10 or water-soluble CoQ10 formulations with hearing-related outcomes were included and synthesized descriptively. Results: Fourteen studies met the inclusion criteria, including randomized controlled trials, non-randomized clinical studies, case series, and case reports. Two distinct therapeutic roles of CoQ10 emerged: in primary mitochondrial hearing disorders caused by defects in mitochondrial DNA or CoQ10 biosynthesis pathways, CoQ10 acted as a replacement therapy and was consistently linked to stabilization or prevention of progressive sensorineural hearing loss. Conversely, in acquired or age-related conditions—including presbycusis, noise-induced hearing loss, ototoxicity, tinnitus, and sudden sensorineural hearing loss—CoQ10 was used as an antioxidant or neuroprotective supplement, with outcomes showing functional preservation, symptom reduction, or decreased cochlear injury. Internal validity varied across studies: most evidence for replacement therapy was derived from observational designs, and antioxidant applications were mainly supported by small or preliminary clinical trials. Conclusions: The available evidence suggests two distinct clinical roles of CoQ10 in hearing disorders: (i) replacement therapy in genetically defined mitochondrial deafness and (ii) adjunctive antioxidant/neuroprotective use in acquired conditions. Given heterogeneity and limited study quality, further well-designed trials are needed before broad clinical recommendations can be made.