Decamethonium bromide is primarily used in medical settings as a neuromuscular blocking agent. It functions by inducing muscle paralysis, which is particularly useful during surgical procedures to facilitate endotracheal intubation and to ensure controlled muscle relaxation. This allows surgeons to operate more safely and effectively. Additionally, it is employed in certain diagnostic procedures where temporary muscle paralysis is required. However, its use has declined over time due to the development of safer alternatives with fewer side effects.