The most common causes of gastritis are:
Certain medications, such as aspirin, ibuprofen, or naproxen, when taken over a longer period of time
Drinking too much alcohol
Infection of the stomach with a bacteria called Helicobacter pylori
Less common causes are:
Autoimmune disorders (such as pernicious anemia)
Backflow of bile into the stomach (bile reflux)
Cocaine abuse
Eating or drinking caustic or corrosive substances (such as poisons)
Extreme stress
Viral infection, such as cytomegalovirus and herpes simplex virus, especially in people with a weak immune
system