Nicotinamide is a component of coenzyme I and coenzyme II, and is a coenzyme for many dehydrogenases. Its deficiency can affect normal cellular respiration and metabolism, thus causing pellagra. What are the clinical uses for it? One is pellagra, stomatitis, tongue inflammation, and then there is atrioventricular block of the heart. Nowadays, niacinamide is put in skin care products to repair the skin barrier and to promote skin repair. What are the contraindications of niacinamide? Some patients may experience flushing and itching of the skin after using it. Some patients may experience nausea, epigastric discomfort, loss of appetite, etc. If used in large doses for a long time, it can cause fetal malformations, so pregnant patients should not use this drug as much as possible. Some people who use it for a longer period of time can develop gastric ulcers. As a drug, it is best to apply it under the guidance of a doctor and stop it once a more serious side effect occurs, and then go to the hospital.