A one year study on 700 smokers with heart disease who took Chantix to help them stop smoking turned up an increased risk of heart attack vs. placebo. Coverage saying "small" increase, but if you notice it in a one year with only 700 people in the study, that's a decent sized signal.
And it's not like Chantix was trouble free before this came out.
I guess if we keep discovering that drugs we are using have a lot of problems and stop using them (as much), that might net out to cheaper health care with better results. In a case like this (stopping smoking by taking a potentially problematic drug vs. continuing smoking), it's a really tough call.