Background: Primary dysmenorrhea, which is highly prevalent in young girls, reduces the quality of life. Given the side effects of conventional chemical drugs and evidence of the analgesic and anti-inflammatory properties of Ziziphora tenuior, this study was conducted to determine the effect of this extract capsules on primary dysmenorrhea.

Methods: This was a triple-blind randomized clinical trial conducted in 2024-2025 on 94 students with primary dysmenorrhea. Research instruments included demographic characteristics questionnaire, menstrual status questionnaire, and Visual Analogue Scale for pain. Participants were randomly allocated into two groups of 47: intervention and control. The intervention group received 500 mg capsules containing Ziziphora tenuior extract, while the control group received 500 mg capsules containing dried bread (placebo) every 8 hours during the first three days of menstruation for two consecutive cycles. Data analysis was performed using SPSS version 20, with a significance level of less than 0.05.

Results: The two groups were homogeneous in terms of demographic variables including age , body mass index, mean age at menarche, and onset of painful menstruation (p>0.05). Also, mean pain severity and duration before the intervention showed no significant difference between the two groups (p>0.05). However, pain severity and duration after the intervention in the Ziziphora tenuior group showed a significant decrease compared to the placebo group, with effect sizes of 0.653 and 0.466, respectively.

Conclusion: Given its effectiveness and fewer side effects, this plant can be considered as an adjunctive treatment option to reduce the symptoms of primary dysmenorrhea in young girls.