No, I have never had mouth sores from Seroquel, or from anything else. I've taken Seroquel or Seroquel XR for years and at various doses up to 800 mg. Are you certain they are from medications? There are myriads of other conditions that can cause mouth sores. Perhaps you should go to your GP if your psychiatrist seriously doubts Seroquel or psych issues (stress cold sores?) are the cause.