I was on Chantix for like 4 months, and did not have one bad side effect. No weight gain or constipation. The drug works really well, if you are commited. I have been off it for 2 months. I have slipped some because of emtional issues that have been going on in my life. I know that is a poor excuse. Its not like I am back to a pack a day or anything. I called in a refill for the chantix and will resume it for a month or two. I hope this info helps!