There are various types of Ranitidine, such as taking Bismuth Ranitidine Citrate may cause darkening of stools, such as taking Ranitidine Hydrochloride usually does not cause darkening of stools. Ranitidine belongs to acid inhibiting drugs, is a common gastric mucous membrane protection drug, the common types mainly include bismuth ranitidine citrate, ranitidine hydrochloride and so on. Due to the large amount of bismuth contained in bismuth ranitidine citrate, which is a black substance and is not absorbed by the intestines, it can color the contents of the intestines black, and consequently, after the formation of stools, the discharged stools show black color; therefore, there is a possibility of black stools when taking a drug like bismuth ranitidine citrate. If black stools occur, it is recommended to go to the hospital immediately to improve the examination to clarify the cause of the disease and standardize the treatment under the guidance of the doctor.