Gallbladder disease (cholecystitis or cholelithiasis): This is often the most common cause of right upper quadrant (RUQ) pain, especially if the pain is severe and persistent. Gallstones can cause obstruction of the cystic duct, leading to inflammation of the gallbladder.

Peptic ulcer disease: Both gastric and duodenal ulcers can cause RUQ pain, especially if the pain is related to eating or worsens at night.
Hepatitis: Inflammation of the liver can cause RUQ pain, and it can be due to viral, alcoholic, or autoimmune causes.
Right kidney stone or pyelonephritis: While kidney stones or infections can cause flank pain, they can also radiate to the RUQ, especially if the stone is in the upper pole of the kidney or if there is significant inflammation.

Appendicitis (with an atypical presentation): Although appendicitis typically presents with right lower quadrant pain, in some cases (especially if the appendix is retrocecal), the pain can be felt in the RUQ.
Myocardial infarction: Cardiac causes of chest pain can sometimes be referred to the RUQ, especially if there is involvement of the right coronary artery.
Pneumonia or pulmonary embolism: Right lower lobe pneumonia or a pulmonary embolism can cause referred pain to the RUQ due to the shared innervation of the diaphragm and the lung.

Hepatic artery aneurysm or thrombosis: These are rare vascular conditions that can cause RUQ pain due to ischemia or rupture of the hepatic artery.
Right adrenal gland pathology (e.g., tumor or hemorrhage): Although rare, diseases of the right adrenal gland can cause RUQ pain due to its location near the liver and kidney.
Intestinal obstruction or volvulus: While these conditions more commonly cause diffuse abdominal pain, they can occasionally present with localized RUQ pain if the obstruction or volvulus involves the small intestine in the right upper quadrant.