Zantac is well tolerated by the majority of people, and its common adverse effects, such as headaches, diarrhea, and nausea, are moderate and only last a few days. Rarely, severe complications such as liver failure, acute porphyria, and pneumonia have been observed. However, the US Food and Drug Administration asked that all ranitidine products be taken off the market in April 2020 due to concerns about contamination with NDMA, a cancer-causing substance.