Decamethonium iodide is primarily used in medical and pharmacological research as a neuromuscular blocking agent. It functions by mimicking the action of acetylcholine at the neuromuscular junction, leading to prolonged muscle relaxation. This property makes it valuable in studies related to anesthesia and muscle physiology, where controlled paralysis is required. Additionally, it serves as a tool in experimental settings to investigate the mechanisms of neuromuscular transmission and the effects of various drugs on muscle function. Its application is strictly confined to research due to its potent effects and potential risks.