Gastritis can be categorized into two kinds: erosive gastritis and non-erosive gastritis, and it can also be classified according to the body part which the stomach affects (such as the cardia, corpora ventriculi, antrum of stomach). Based on the types of the inflammatory cells, gastritis can be further categorized into acute gastritis and chronic gastritis in histology. However, there is no means of classification so far can tally exactly with the pathophysiologic symptoms of the disease and different classifications still may overlap. There is an old saying goes that every medication has side effect. Most medication need to be transmitted, digested and absorbed through the gastrointestinal system, so the gastrointestinal tract bears the brunt of being irritated and harmed by certain medication.  

Clinical data shows that the number of patients who suffer from gastritis, gastrointestinal ulcers and haemorrhage or other such kind of disease due to their using medications inadvertently, accounts for over one third of the total number of gastritis patients, and it tends to increase year by year.

Clinical treatments indicate that the common medications which cause gastritis are Salicylic Acid preparation (Aspirin, Acetyl salicylic acid compound), Phenylbutazone, Indomethacin, adrenal cortical hormone, antibacterial and anti-inflammatory medications   (Trimethoprim-sulfamethoxazole, Tetracycline, Erythromycin), and other medications such as Digitalis, Reserpine, antihistamine drug; can also cause gastritis. The reasons why those medications can cause gastritis are explained as follow.

1. Those medications inhibit the secretion of prostaglandin E from stomach lining. Prostaglandin E can protect the stomach lining. When the secretion of Prostaglandin E was inhibited or reduced, it can result in damage to the stomach lining and cause inflammation, and this often occurs after taking Phenylbutazone or Indomethacin.

2. Those medications reduce the secretion from stomach lining gland; change the component of the secretion from stomach lining gland; weaken the protective function of the stomach lining; increase the secretion of gastric acid and pepsin; inhibit the reproduction of epithelial cells of the stomach lining. Taking prednisone in large dosage for long time can cause gastritis, gastrointestinal ulcers, even stomach perforation.

3. Those medications destroy the lipoprotein in the epithelial cells of the stomach lining. Taking stimulant medication orally for a long time can cause hydrogen gene penetration into stomach lining, expansion of damage to stomach lining, and lead to the assimilation of the stomach lining by pepsin; thus result in erosion and haemorrhag. At the same time, in the acid environment in the stomach, too much salicylic acid can directly destroy the lipoprotein in the epithelial cells of the stomach lining, and make the stomach lining protection being destroyed and cause the gastritis.

 Patients with a history of gastritis should choose enteric medication, such as Aspirin, Erythromycin, or choose injection, and try not to choose oral administration 

Patients who take non-enteric medication must take it after meal. People who take stimulant medication orally for a long time must take medication that can protect stomach lining such as aluminum hydroxide) at the same time and the dosage must be controlled.