Alcohol is an irritant and a diuretic and can cause ulcers in the stomach as a result of the alcohol eating away at the lining, as well as affecting the oesophagus causing chronic heartburn and bleeding.
The stomach is coated by a thick mucosal lining, which protects the stomach tissues from its own hydrochloric acid production. Small or moderate amounts of alcohol are generally tolerated in most people. However, over use of alcohol can increase the production of this acid, causing GERD or gastritis (inflammation of the mucosal stomach lining.) Gastritis causes nausea, vomiting, stomach pain or aching, and a sense of fullness. Long term abuse of alcohol can lead to the underproduction of stomach acid, or hypochloridia . Exposed stomach tissues due to alcohol abuse can become vulnerable to tearing and lead to internal bleeding.
Besides acid reflux, alcohol abuse can lead to chronic vomiting and dry heaves, which puts extra stress on the esophagus. This can cause tearing of the mucus membranes, leading to serious internal bleeding, called Mallory-Weiss syndrome.
If certain conditions such as chronic GERD, acid reflux or gastritis are already present, alcohol can exacerbate the issue. Because alcohol is a relaxant, it affects the LES (lower esophageal sphincter) by making it weak or loose and therefore allowing stomach acid to rise up into the esophagus, causing heartburn and eventually, esophageal damage.