This is an odd question, but I wondered if anyone else agrees with me on this...
I've had acne since at least age 11, and I've never used any treatment that made my skin "purge" or get worse before it got better. If my skin became worse (as in having a lot more acne), or didn't improve almost immediately, the treatment never worked in the long run. I was always very fastidious about following the doctor's treatment protocol, so it wasn't as if I didn't "wait long enough" for the medication/treatment to work.
I've been on Accutane twice, and neither time then did I have a "worse" period before my skin improved. The acne that was already existing on my skin became slightly more red and tender, but my skin didn't break out before it improved.
After being off Accutane for a couple months recently, the doctor put me on Acanya gel and Tazorac since I was having a very slight relapse. The Acanya gel didn't work when I used it on my skin prior to my second round of Accutane, but this time it seems to help-- again, though, I didn't have to endure any "skin purging" before my skin cleared up.
I can't think of any other medical problem, aside from treatment for cancer, where a person is expected to deal with worse symptoms before improvement! It's not as if you go to see the doctor for an ear infection, he/she gives you antibiotics, and you're told "Your ear is going to hurt a lot more for a while, and THEN it will get better!" It seems almost like a cop-out, since acne (at least for me) seems to go in cycles. Sometimes it will get better on it's own. If I wait six weeks for my skin to "purge", it will almost always go through a week or two where it's better, and then will get worse.