When mice can choose when to get nicotine (like smoking), they don’t eat less or lose weight on normal food — but they do if they’re on junk food, showing nicotine’s effect depends on what and when you eat.

Even when young rats got nicotine, they didn’t gain more or less weight than rats that got a fake pellet — as long as they all ate the same amount of food.

People who smoke tend to weigh less than non-smokers, and when they quit, they usually gain about 4 kg because their body goes back to how it normally weighs without nicotine.