Gallamine triethiodide is primarily used as a neuromuscular blocking agent in medical settings. It functions by competitively inhibiting acetylcholine at the neuromuscular junction, leading to muscle relaxation. This makes it valuable in surgical procedures where muscle paralysis is required to facilitate endotracheal intubation and controlled ventilation. Additionally, it is utilized in certain diagnostic procedures to prevent involuntary muscle movements that could interfere with accuracy. However, its use has declined with the advent of newer agents with fewer side effects.