Gastroesophageal Reflux Disease (GERD) with Esophagitis: This condition is a common cause of vomiting blood due to the erosion of the esophageal lining, leading to bleeding. The frequent exposure of the esophagus to stomach acid can cause ulcers and bleeding.

Peptic Ulcer Disease: Both gastric and duodenal ulcers can erode into blood vessels, leading to significant bleeding and vomiting of blood. The use of NSAIDs and Helicobacter pylori infection are common risk factors.
Gastritis: Inflammation of the stomach lining can lead to erosion and bleeding. This can be caused by alcohol, NSAIDs, stress, or infections.
Mallory-Weiss Syndrome: This condition involves tears in the mucous membrane or lining of the lower end of the esophagus, where it connects to the stomach. These tears can bleed, and the blood may be vomited up.

Esophageal Varices: These are enlarged veins in the esophagus that can bleed easily due to increased pressure from the liver. This condition is often associated with liver cirrhosis and portal hypertension. Missing this diagnosis can be fatal due to the high risk of severe bleeding.
Aortic Enteric Fistula: Although rare, this condition involves a fistula (abnormal connection) between the aorta and the gastrointestinal tract, which can lead to massive bleeding.
Boerhaave's Syndrome: A rupture of the esophagus, which can lead to severe bleeding and is a medical emergency.

Dieulafoy's Lesion: A rare cause of gastrointestinal bleeding characterized by a small mucosal defect with an exposed, usually large, caliber artery at its base.
Hemobilia: Bleeding into the biliary tree, which can lead to vomiting blood, though this is more commonly associated with melena (black, tarry stools) or hematemesis (vomiting blood) mixed with bile.
Tumor Bleeding: Bleeding from a gastric or esophageal tumor, which can present with vomiting blood. This is less common but should be considered, especially in patients with risk factors for cancer.