Ingestion of capsaicin-containing foods causes a burning sensation to the mouth that can be unpleasant (although some people find it enjoyable, possibly due to endorphin release[1]). Topical capsaicin can result in a burning sensation at the application site.
Capsaicin can provoke adverse gastrointestinal (GI) symptoms (e.g., abdominal pain, diarrhea, and heartburn), especially in high dosages and in people with GI disorders (e.g., irritable bowel syndrome, gastroesophageal reflux disease (GERD)).[2][3][4][5] There is some evidence that GI symptoms subside with regular consumption, although more research is needed.[6][7]
Case-control studies have frequently observed an association between chili pepper consumption and a higher risk of stomach cancer.[8] However, this finding remains controversial, given the limitations of case-control evidence and the fact that the China Kadoorie Biobank study, one of the highest quality studies on the topic, found that people who ate chili peppers more frequently actually seemed to have a lower risk of stomach cancer.[9]