Introduction: Primary dysmenorrhea is characterized by pain during menstruation without any pelvic pathology. It is a common problem among females in their reproductive age. However, exercise is a known intervention to relieve the symptoms. This study aimed to assess the effect of core stability exercises on pain severity, pain duration, and drug consumption in primary dysmenorrhea in adult females. Materials and Methods: Thirty-four non-athletic, unmarried girls, aged 18-25 years, who suffered from moderate to severe primary dysmenorrhea, were randomly assigned to the experimental (n=17) and control groups (n=17). The experimental group performed 8 weeks of core stability exercise (3 sessions/week, 45-60 min/session). Before and after the exercise program, pain intensity, pain duration, and the medication usage of the participants were assessed by “Numeric Pain Scale” (10-point scale), “the number of hours that the pain continued” and “the total amount of painkiller consumption for the pain reduction” for 2 days prior to menstruation, and 2 days after menstruation onset. The statistical analysis was performed using ANCOVA and dependent t-test. The confidence interval was considered at 0.95 (α<0.05). Results: In comparison with the control group, there was a significant decrease in pain intensity (P=0.008), pain duration (P=0.021), and the number of painkillers consumed (P=0.018) in the experimental group. Conclusion: Core stability exercises may be effective in reducing pain intensity, pain duration, and consumed painkillers.