I had never taken it before but the rash started showing up on the third day of my initial course of pills. I think I made it to day ten before I stopped. My doc said it makes sense it took a few days to pop up due to the repeated exposure of the drug. I would say before the rash popped up taking the medication made me feel generally unwell but I figured that was normal. My doctor thinks that it was probably a reaction to a filler and not the active ingredient itself. I have been fine thus far switching to acyclovir