Objective: The primary objective of this study was to examine the effect of HypericumPerforatum on mitigating premenstrual syndrome symptoms in comparison to a placebo among female patients seeking treatment at the Apadana Clinic in Yasuj City. Method: The present study comprised double-blind clinical research involving 105 Iranian women diagnosed with premenstrual syndrome (PMS). These participants were selected through random selection and subsequently assigned to two groups, namely HypericumPerforatum, and placebo, using random categorization. The Premenstrual Symptoms Screening Questionnaire (PSST), which has been standardized for Persian speakers, was employed for data collection. The repeated measures statistical method was employed in this study due to the inclusion of two distinct groups and the implementation of three assessments: pre-test, post-test, and follow-up. The data analysis was conducted using SPSS version 26. Results: The results of the present study revealed that there was no statistically significant difference (P>0.05) in the demographic factors between the two groups. Furthermore, the analysis of the data revealed that Perforan, in comparison to the placebo, exhibited a statistically significant reduction in the severity of symptoms associated with premenstrual syndrome (F=4.041, P<0.05). Additionally, the statistical analysis revealed that both the effect of time (P<0.05, F=29.189) and the interaction effect between groups and time on the severity of premenstrual syndrome (PMS) symptoms are statistically significant (P<0.05, F=5.825). Conclusion: The results of the present study indicate that the administration of Perforan leads to a reduction in the severity of premenstrual syndrome (PMS) symptoms when compared to a placebo. Nevertheless, the limited number of clinical trials conducted in this particular domain necessitates further investigation and research.