Figure 2. The first phase of the study will prospectively assess symptom changes throughout the menstrual cycles on continuous fixed-dose treatment. For patients who have less than 2 of 3 symptomatic cycles, the trial ends after the lead-in phase. Those with at least 2 of 3 symptomatic cycles will progress to the second phase of the trial. All patients will continue to receive the standard fixed-dose. Patients are randomized to receive an additional dose premenstrually of either medication or dummy. The patients are crossed-over to the other group multiple times.