I took Bactrim for about 1 and 1/2 years. I then went through a period where my skin broke out very badly for about two months and went back to Bactrim for about another 8 months. I never had any bad side effects; atleast not visible, or so much physically. However something to remember is that your body becomes dependant whenever you take an antibiotic for such a long time. Basically the bactrim will not only kill the bacteria but also your white blood cells and other friendly bacteria. However it definetly helped clear up my skin almost amazingly while I was taking it.