Gastritis is divided into erosive gastritis and non-erosive gastritis. Gastritis can also classify into different kinds according to the different parts of the stomach (such as cardia , body of stomach, antrum of stomach). According to the types of inflammatory cells gastritis can be further divided into acute gastritis and chronic gastritis from the point of histology. However, there is no a classified method consistent with pathophysiology, and a variety of classifications are overlapping. The saying goes: "one thirds of drugs are toxic." Vast majority of drugs have to pass through the gastrointestinal system, being digested and absorbed, so gastrointestinal tract bears the brunt of certain drugs’ stimulation and damage.

According to clinical data people who suffer diseases, such as gastritis, gastrointestinal ulcers and bleeding, which are caused by inadvertently taking drugs, account for about one-third of the total number of patients who have stomach trouble, which is an increasing trend year by year.

 Clinical findings showed that commonly used drugs causing gastritis are mainly salicylic acid preparations (aspirin, aspirin compound tablet), butazone, indomethacin, adrenal cortical hormone, and anti-bacterial anti-inflammatory drugs (such as SMZco, tetracycline, erythromycin). Other drugs, such as digitalis , reserpines, and antihistamines , can also cause gastritis. Why these drugs would cause gastritis? There are the following main reasons: 

1．Inhibiting gastric secretion of prostaglandin E. Prostaglandin E has the function of protecting gastric mucosa, so the suppression and reduction of prostaglandin E secretion can cause gastric mucosal injury and inflammation after taking phenylbutazone or indomethacin.

  2．Reducing the secretion of gastric glands; changing the composition of glandular secretion; weakening the protective role of gastric mucosal barrier; increasing gastric acid and pepsin secretion; inhibiting gastric epithelial cell regeneration. Substantial use of prednisone can cause gastritis and gastrointestinal ulcers, even perforation. 

 3．Undermining lipoprotein layers of the gastric epithelial cells. Long-term orally taking pungent drugs (salicylic acid preparations) can cause the infiltration of hydrogen ions into mucosal, the expansion of mucosal injury to gastric mucosa which would be digested by pepsin digestion. Then this results in stomach erosion and bleeding. At the same time, under the acid environment, a large amount of salicylic acid can directly damage the lipoprotein layer of the epithelial cells on the gastric mucosa and result in damage of gastric mucosal barrier, which leads to inflammation.

People who suffer from gastritis should chose drugs with enteric solubility, such as enteric-coated aspirin, erythromycin, or take injection, not take by mouth as much as possible. 

Non-enteric-coated drug-taking patients must take drugs after a meal. Long-term- pungent- drug-taking patients must simultaneously take the gastric mucosa protective drugs (such as aluminum hydroxide), and control the dose.