The objective of this triple-blind trial is to determine effect of combined calcium-vitamin D and only calcium on pain and bleeding in students with primary dysmenorrhea. Ninety students with moderate to severe dysmenorrhea residing in Tabriz dormitories will be allocated into three groups with allocation ratio 1:1:1 and block sizes of 3, 6 and 9. The participants will take combined (1000 mg calcium and 5000 IU vitamin D), only calcium (1000 mg), or placebo tablets daily from approximately 14 days before starting menstrual flow until relieving dysmenorrhea pain in the next cycle (about 18 tablets each cycle) for 3 consecutive cycles. The tablets are identical in terms of size, color, etc. To maintain blinding, a person not involved in the recruitment and data collection will determine allocation sequence and will put the tablets in opaque sealed consecutively numbered envelopes. Gelofen tablets will be given to all participants to use to relieve menstrual pain, if needed. Primary outcomes are pain severity and bleeding amount which will be assessed by visual analogue scale and Hygam chart, respectively. Secondary outcomes are quality of life (assessed by SF36), the number of taken analgesics (Gelofen), satisfaction with treatment and adverse events. Outcomes will be assessed during three months under intervention and one month after intervention. ANCOVA and repeated measurement tests will be used to compare the groups in terms of pain score, amount of bleeding, quality of life, and the number of taken analgesics. Satisfaction with treatment will be compared using Mann-Whitney test.