Why does chantix give you terrible gas and crazy dreams?

Side effects: All drugs have side effects, and GI symptoms (increased gas, nausea, vomiting, diarrhea or constipation) are among the most common, whether with Chantix or any other drug. Chantix acts on nicotine receptors in the brain, and weird dreams and nightmares are extremely common. Increased depression and suicidal thoughts can also occur, but are less common. Stopping smoking is critical, Chantix helps.