I have gained 20 lbs in about 4 to 6 months after just 4 weeks of taking the chantix. I stoped the medication after 4 weeks and have been smoke free for a year now But have gained belly fat. Is this normal and have there been others with the same side effect. I know my father took chantix and has also gained 20 lbs of belly fat. He has be smoke free for 9 months after 60 years of smoking. So I will say that it has worked for us. I just don't like the weight gain ( belly fat)