A phase III, randomized, placebo-controlled, double-blind trial of flaxseed for the treatment of hot flashes: North Central Cancer Treatment Group N08C7.

Objective: Preliminary data suggest that flaxseed, a rich source of dietary lignans, may be a potentially effective treatment of hot flashes. A phase III, randomized, placebo, controlled trial was conducted to evaluate the efficacy of flaxseed in reducing hot flashes.

Methods: Postmenopausal women with or without breast cancer were randomly assigned to a flaxseed bar (providing 410 mg of lignans) for 6 weeks versus a placebo bar. Participants completed daily, prospective, hot flash diaries during the baseline week, and then ate one study bar per day for 6 weeks while recording their daily hot flashes. The intraparticipant difference in hot flash activity between baseline and the last treatment week was the primary endpoint. Adverse effects were evaluated through a self-report and the Common Terminology Criteria assessment.

Results: A total of 188 women were enrolled in this trial. The mean hot flash score was reduced 4.9 in the flaxseed group and 3.5 in the placebo group (P = 0.29). In both groups, slightly more than a third of the women received a 50% reduction in their hot flash score. Only one adverse effect was significantly different between groups, grade 1 pruritus, which was more common in the placebo group (8% vs 1%). Both groups reported abdominal distension, flatulence, diarrhea, and nausea. Adherence and ability to detect treatment assignment did not differ between groups.

Conclusions: The results of this trial do not support the use of 410 mg of lignans for the reduction of hot flashes. The bars were fairly well tolerated, with both groups reporting gastrointestinal effects, probably due to the fiber content.