I use Zithromax and still have flare ups. I notice when I'm sicker and in need of a tune up, my acne will be worse. I've been told its cuz acne is caused by bacteria and we always have some sort of bug reeking havoc. But right now my face is clear, I'm on Zpac, but also just had a tune-up in March. So....I'm not convinced Zpac does squat for me but the bacteria thing does make sense...