Histamine diphosphate is widely used in medical and research settings. It serves as a key reagent in diagnostic tests, particularly for assessing allergic reactions and hypersensitivity. In clinical studies, it is employed to evaluate the responsiveness of histamine receptors, aiding in the development of antihistamine drugs. Additionally, it is used in physiological research to study the role of histamine in various bodily processes, such as immune response, gastric acid secretion, and neurotransmission. Its application in skin prick tests helps diagnose allergies by inducing a controlled histamine response for comparison with allergen reactions.