Although topical steroids constitute the first-line therapy for recurrent aphthous ulcers (RAUs), their long-term use often leads to candidiasis. Although cannabidiol (CBD) can be an alternative for pharmacologically managing RAUs due to its analgesic and anti-inflammatory in vivo effects, there is a lack of clinical and safety trials concerning its use. The aim of this study was to evaluate the clinical safety and efficacy of topical 0.1% CBD for managing RAU. A CBD patch test was performed on 100 healthy subjects. CBD was applied on the normal oral mucosa of 50 healthy subjects 3 times/day for 7 days. Oral examination, vital signs, and blood tests were performed pre- and post-CBD use. Another 69 RAU subjects randomly received one of three topical interventions: 0.1% CBD, 0.1% triamcinolone acetonide (TA), or placebo. These were applied on the ulcers 3 times/day for 7 days. The ulcer and erythematous size were measured on day 0, 2, 5, and 7. Pain ratings were recorded daily. The subjects rated their satisfaction with the intervention and completed a quality-of-life questionnaire (OHIP-14).