Chantix is a medication that acts in the brain in a similar way that nicotine acts. Because of that, the drug will have similar effects on the brain as nicotine. This is why it can work to help you quit smoking. The only difference is that since nicotine has such a short life in the body, it isn't effecting your brain at night when you are sleeping and not smoking. Chantix on the other hand is effecting your brain at night. It turns out that nicotine has a great effect on your ability to remember things in the short term. In fact, it enhances short term memory. So it is possible that Chantix is not causing you to have a nightmare, but rather it is causing you to remember these dreams that you otherwise were having anyway, but were not remembering. At any rate, the chantix is almost certainly responsible for these symptoms.
I suggest that you schedule an appointment with your primary care physician
. He or she can listen to your symptoms and decide if there is any other possible explanation for these dreams. If there is not, then the two of you can discuss the pros and cons of staying on the Chantix.