Nicotine does have a laxative effect. Most people who quit smoking deal with constipation for a while.
Since you know this is going to be an effect for you WHEN you quit smoking (
), go ahead and plan for it. Increase fiber, water and physical activity in your daily routines. All of this will help you with the quit, too. Something that worked for me, too, (and still does if I have a bout of constipation) is a serving of fruit juice before bedtime. Not just apple or orange juice, either. A can of apricot nectar or a glass of plum juice does the trick.
Do not go back to smoking because you're constipated. That's just crazy! Deal with the constipation that way most of us ex-smokers had to. A brisk walk, fiber, lots of water and a daily serving or two of extra-special fruit juice will help both the constipation and craves
Best of luck to you!