http://www.medications.com/effect/view/32035 I really like the Zpak. I have taken it several times from things like sinus infections to lung infections. I never experienced any side effects but this time I am experiencing severe smelly gas. I don't know why but I never have such smelly bad gas before. Fri, 01 Aug 2008 21:03:47 -0400 http://www.medications.com/effect/view/32035?item=10676 I had a friend with that experience from the z pac. The gas was actually a result of colitis. This can be very serious if left untreated. I would see a doctor if symptoms do not pass. Hopefully it is not and it is just symptoms of your healthy bacteria http://www.medications.com/effect/view/32035?item=10676