Methods: A 3-month retrospective history and 1-month prospective baseline (run-in) period is used to assess the baseline attack frequency. The study setting is actually triple-blinded (participant-blind, investigator-blind, sponsor-blind). Placebo preparation with design and package identical to the test preparation will be used. Parallel group design instead of cross-over design is used. Randomization will be performed using a random number generator, with blocks size of 4, and creating unique randomization codes for each subject. The stratified randomization is based on the attack frequency is used as the stratification variable, using 4 attacks per month as the cut-off for low-and high frequency.