In a double-blind, placebo-controlled, parallel group, multicenter study, 555 women with moderate to severe mastalgia were randomized to one of the four treatment groups to receive (a) gamolenic acid (GLA) and antioxidants, (b) placebo fatty acids and antioxidants, (c) GLA and placebo antioxidants, or (d) placebo fatty acids and placebo antioxidants, for four menstrual cycles. This was followed by a further eight menstrual cycles of open treatment in which all patients received GLA, but continued to be randomized to active or placebo antioxidants as in the preceding parallel phase. Diary pain cards and linear analog charts were used for assessment of response. A reduction in breast pain was seen in all four treatment groups during the blinded treatment phase. There was a substantial improvement in the placebo fatty acids groups (response rate of 40%), and there were no significant differences among the four treatment groups. During the open treatment phase, a further reduction in breast pain was seen in all groups, with no statistically significant differences between groups. This study showed that GLA (Efamast) efficacy did not differ from that of placebo fatty acids, regardless of whether or not antioxidant vitamins were present.