Day 12 after quitting smokingThe slow gut

By Yevhenii, who smoked for 26 years · Updated 30 Oct 2026 · 2 min read

What's happening in your body

Nicotine speeds up the movement of the bowel, which is why the first cigarette of the day so often worked like a switch. Without it the gut runs slowly for a while. In a study of more than a thousand people at a stop smoking clinic, about one in six became constipated, and about one in eleven went from no trouble at all to being very or extremely constipated. It was worst at two weeks and was still above its old level at four, when the study stopped measuring.

What to expect

Bloating, discomfort, a routine that has stopped being routine. It is rarely mentioned in leaflets and it genuinely bothers people, so it helps to know it is a recognised effect of stopping and not a sign that something is wrong. It peaks around now. In the same study the rise was smaller in people using nicotine replacement, which fits the explanation.

The gut is reacting to the missing nicotine, not to the missing cigarette. The study did not follow people past four weeks, so there is no good figure for when it ends; what the numbers do show is that the worst of it comes early. See a doctor rather than waiting if there is blood in the stool, strong or worsening pain in the belly, vomiting or unexplained weight loss, or if nothing has helped after a few weeks.

What else you could do

More water through the day. Fibre from real food, such as oats, beans, pears, prunes and wholegrain bread, added gradually so that the bloating does not get worse. A walk after meals, because moving the body helps move the gut. If a week of that has not helped, a pharmacist can suggest a gentle laxative that suits you.

Sources. Hajek P, Gillison F, McRobbie H. Stopping smoking can cause constipation. Addiction, 2003.