Introduction: Oral lichen planus (OLP) is a chronic mucocutaneous disease with an immunological etiology. This study was conducted to evaluate the effect of coenzyme Q10 (CoQ10) as an adjunctive to topical corticosteroids in the treatment of erosive–ulcerative lichen planus. Materials and methods: A total of 30 patients with a confirmed clinical diagnosis of OLP participated in this clinical trial. Patients were randomly allocated into one of two groups and treated as follows: group I received topical corticosteroids and group II received CoQ10 combined with topical corticosteroids. Assessment of outcome measures including clinical score and pain was carried out at the time of initial visit (baseline) and at 2, 4, 8, and 12 weeks following treatment protocol. All recorded data were analyzed using paired t-test and independent t-test. The level of significance was established at a P value of 0.05 or less. Results: The two studied groups showed a marked reduction in pain sensation and size of lesions, particularly in the final follow-up period. However, healing and decrease in the size of the lesions were effective in group II, and a significant difference was found between the two groups favoring group II over group I. Conclusion: CoQ10 in combination with topical corticosteroids was found to be effective in managing ulcerative lesions of OLP; however, more studies with a larger sample sizes and longer duration with evaluation of the adjunctive effect of CoQ10 on inflammatory markers expressed in OLP are recommended.