According to boasts by Pfizer, the drug's maker, "approximately one-in-five" users quit smoking for a year. This boast is based on their own study in which the subjects received intense counselling sessions for a entire year.
Pfizer's five clinical trials of varenicline were published in July and August 2006. Three are comparable in that they involved a 12-week treatment period using 1mg of Chantix twice daily. In the Chantix study headed by Gonzales, 21.9% of Chantix users were still not smoking at one year. In Oncken the rate was 22.4% and in Jorenby 23%.
That's an average one-year rate of 22% or, on the flip side, a relapse rate of 78%. But these rates were achieved under highly artificial clinic study conditions. History and common sense teach that use under real-world conditions will likely generate a significantly higher failure rate.