Study aim: The effect of epigallocatechin gallate (extracted from green tea) loaded nanostructured lipid carriers on the treatment of oral lichen planus Design: controlled clinical trial, phase 3, with two-parallel groups, duble -blind Settings and conduct: This study will be conducted in the clinics of the University of Medical Sciences and the dental faculty of Tabriz. The random assignment sequence will be determined by a person not involved in the study using G-Power software. To conceal the allocation of drugs , it will be placed in opaque, sequentially numbered bottles. Qualified people will be placed in two intervention and control groups using the random block method with a block size of 6 and with a 1:1 allocation sequence. Participants/Inclusion and exclusion criteria: Inclusion Criteria: Definite Diagnosis of Lichen Planus via clinial criteria and histopathology, approvement range of 17 to 70 years old؛ Exclusion Criteria: pregnancy or breastfeeding, usage of Immuno supressor Drugs. Intervention groups: Intervention group: Mouthwash containing Epigallocatechin gallate loaded nanostructured lipid carriers will be used 3 times a day, 5 cc each time for 4 weeks. Control group: Mouthwash containing Epigallocatechin gallate will be used 3 times a day, 5 cc each time for 4 weeks. Main outcome variables: Pain intensity, lesion size, Thongprasom scale