Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 20 0 2023 06 11 1 8 Gohar Eslami Cardiovascular Research Center, Mazandaran University of Medical Sciences, Sari, Iran Anahita Ghorbani 3. Department of Oral Medicine, Faculty of Dentistry, Mazandaran University of Medical Sciences, Sari, Iran Jafar Akbari Department of Pharmaceuticals, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran Ali Farmoudeh Department of Pharmaceuticals, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran Fereshteh Faghih Department of Oral Medicine, Faculty of Dentistry, Mazandaran University of Medical Sciences, Sari, Iran Minoo Moghimi Department of Clinical Pharmacy, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran 2020 05 07 2021 07 14 Objectives: This study aimed to assess the efficacy of oral mucoadhesive N-acetylcysteine (NAC) tablets for treatment of recurrent aphthous stomatitis (RAS). Materials and Methods: Forty-nine patients with RAS were randomized to receive mucoadhesive NAC tablets (n=25) or placebo (n=24). Tablets were prescribed three times a day for 7 days in each group. Pain intensity was evaluated with visual analog scale (VAS) three times a day from day 1 to day 7. Also, patients were clinically examined on days 0 (before entering the study), 3, 5, and 7 using a metal caliper to measure the diameter of the lesions. The data were statistically analyzed and P<0.05 was considered statistically significant. Results: Regarding the VAS score, all participants in the treatment group showed complete recovery on day 7 (P<0.01). Also, the diameter of the lesions was significantly smaller in the treatment group than the placebo group at the end of the study (P<0.001). Conclusion: The results of this clinical trial showed for the first time that mucoadhesive NAC tablets can significantly decrease pain and the diameter of RAS lesions without any systemic complications. https://fid.tums.ac.ir/index.php/fid/article/view/3577