Yup... I've had a few. The one that scared me the most was a blood boil near the roof of the mouth. The typical white caps and blisters seem to set in the first month but they quickly receded. I have been told to brush more often, drink lots of water and to see a dentist to get my teeth cleaned. (Which is a great idea for anyone who quits smoking) The best advice I have heard was changing the PG/VG blend to a higher VG. IE; 30/70 or 20/80. Some have even mention going 100% VG. In my own experience, the 30/70 blend seems to help, but I've only been doing that for a few weeks, so the jury is still out on that theory. My doctor did tell me that he wants to be kept in the loop, since cancer runs pretty high in my family and that he really has not seen a lot of good factual studies for long term use of e juice.