Objective: Study on effects of topical Nigella sativa seed oil in treatment of cyclic mastalgia. Study population: Women with cyclic mastalgia attending the Yazd Shahid Rahnemoon hospital (Iran). Sample size: 150 patients. Inclusion criteria: Iranian outpatient females with cyclic mastalgia, patients aged 25-45 years; patients with regular menstrual cycles; patients with cyclic mastalgia diagnosis based on history of cyclic mastalgia for at least the past 3 consecutive cycles, patients with pain duration of at least 7 days per month and mastalgia severity score greater than 4 on a 10 centimeter visual analogue scale requiring pharmacotherapy. Exclusion criteria: Patients receiving hormone therapy or hormonal contraceptive; patients with irregular menstrual cycles; patients with history of breast and endometrial cancer, hysterectomy and bilateral oophorectomy; pregnanct women; brest-feeding women; women planning pregnancy; women with serious health problems. Intervention: Each of the Nigella sativa seed oil, diclofenac and placebo gels is separately applied 2 times daily to the site of breast pain in a group of 50 women with cyclic mastalgia. At the end of the study, the drugs effects on the 10 centimeter visual analog pain score are determined and compared with each other.