There is no serious danger if you take a few puffs of smoke from a cigarette when you’re on nicotine replacement therapy. The problem is when you smoke many cigarettes in a day. This can lead to nicotine poisoning and even death in severe cases. Another side effect of smoking while on nicotine therapy is that it will increase your body’s tolerance to nicotine. This will increase your chance to relapse back to smoking. And in the best case, it will take you longer to wean out of taking nicotine lozenges. Therefore, the takeaway is, even though it is dangerous per se, it is not at all a good thing to do.