I was on brevicon for about 9 months which i believe is the generic form of modicon, im not totally sure. But i know the pills are very similar. Anyway, anytime i missed a pill, and took two pills in one day, i ALWAYS had break through bleeding, which drove me crazy. It's nothing to worry about, its just really really annoying. The best thing i found to avoid break through bleeding, was if i missed a pill, and had to take two pills in one day, i'd take one pill wait five minutes, and then take the next pill. and somehow it didn't cause break through bleeding. But after nine months i went off brevicon and onto another pill.