Varenicline
"Read the product Warnings.  If you have an auto-immune disease pay attention to side effects, specifically a flu-like feeling at 3 weeks after starting Chantix, then followed by mouth ulcers.  Get immediate medical attention if these appear.  On day 21-22 I felt terrible, just like I had the flu.  On day 24 I noticed several Aphthous Ulcers (something I had never had before).  These progressed to a level that I had to go to the ER on day 26.  On day 25 I discontinued Chantix and on day 38 I am still being treated for this. This response has been repeatedly associated with Chantix and some other drugs as well.  Pay attention to side effects and any unusual symptoms."