Smoking has been linked to many illnesses of the digestive tract. Some of these are relatively minor, such as increased belching, bloating and heartburn. Others are more serious, such as peptic ulcers, liver impairment and Crohn's disease. Finally, smoking can cause cancers in the digestive tract, including the mouth, throat and esophagus.

The effects of smoking on the digestive tract vary in severity. For example, the negative effect of smoking on the body’s ability to produce sodium bicarbonate – a substance that helps neutralize the stomach acid that contributes to ulcers – appears to last for only about 30 minutes after the patient stops smoking a single cigarette. Patients who smoke and later quit remain at increased risk for developing Crohn’s disease during their lifetime.