An open-label pilot study over 4 months to evaluate the effectiveness of a compound formulation of ingredients, which individually have been demonstrated to be implicated in the pathogenesis of premenstrual syndrome to ameliorate the most troublesome symptoms of the condition. The supplement provided thiamine, riboflavin, pyridoxine, vitamin D, soy isoflavones, rosemary extract, and krill oil and was taken each day for the 3 months of the trial. Statistically significant effect was reported by the 29 women who completed the study in relief of anxiety, bloating, mood swings, breast tenderness, skin outbreaks, food cravings, fatigue, forgetfulness, insomnia, and headache after 3 months of treatment compared with baseline. This pilot study indicates the formulation to be effective, and a larger placebo-controlled trial is now planned.