My son took it for 20 weeks...the usual time is 16 weeks, but his was very bad so they gave him the extra 4 weeks. Our doctor also told us that you can repeat it, but not for 2 years.
I would say that it cleared up about 90% of his acne. But he had that last little bit that wouldn't seem to clear up.
Then after about 9 months it started getting bad again. Since I knew we couldn't repeat the Accutane just yet, I bought him ProActive. He used it for about 2 months and it finished clearing up the rest of his acne that the Accutane didn't take care of! That has been about 7 years ago and his face is still clear!
He had no serious problems from the Accutane but he said the dry mouth was REALLY annoying. His skin did get a little dry, but some light moisturizer took care of that.
To do it over again, I think we might try the ProActive first. Then if that didn't work we'd try the Accutane. The ProActive is definitely cheaper and has no side effects as they include a moisturizer for the dry skin it may cause.
Not affiliated with either ProActive or Accutane...just our personal experience.
Edited to add: We tried the antibiotic route before the Accutane and it didn't work for him at all.