The Excedrin cycle is totally real and totally horrible. I used to go through that frequently. I couldn’t figure out how a medicine formulated for headaches could make them worse and come back even worse than before. An ER doctor explained the science — which I have long since forgotten — but it was enough for me to switch to Advil for non-migraine headaches. That same ER doctor told me in no uncertain words that he and many of his peers would take Excedrin off the market if they had the power to do it.