Materials and Methods: In this study, 63 students with primary dysmenorrhea were randomly allocated into 2 intervention (receiving one tablet a day combined 600 mg calcium carbonate and 300 mg magnesium stearate, or only 600 mg calcium carbonate from 15th day of cycle until no pain day on the following cycle) and 1 placebo groups. The subjects filled in a diary including pain intensity (0-10 visual analog scale) and rest length for 2 cycles before intervention and 2 cycles under intervention. Univariate general linear model was used for data analysis.

Results: One from each intervention groups were lost to follow up. Both combined calcium- magnesium and calcium alone groups had better outcomes than the placebo group in pain intensity (adjusted difference -1.9, 95% CI -2.2 to -1.7 and -0.9, -1.2 to -0.6, respectively), rest length (-2.5 hours, -3.2 to -1.9 and -1.7, -2.4 to -1.1) and number of Ibuprofen taken (-2.6, -4.1 to -1.1 and -1.5, -2.9 to -0.1). The calcium-magnesium group had significantly better outcomes than the calcium group in pain relief and rest length but not in the Ibuprofen group. No side effect was reported.

Conclusion: Both combined calcium-magnesium and calcium alone are effective in relieving the pain and decreasing the rest length due to primary dysmenorrhea, but better efficacy was obtained from combined calcium and magnesium in comparison with its counterpart.