How are competitive (non depolarizing) blockers?

Curare (d-Tubocurarine) was first drug capable of blocking neuromuscular junction. D-d-Tubocurarine is a prototype agent in this class, naturally occurring mono-quaternary alkaloids, largely replaced by other agents due to side effects (allergisant), increased safety of anesthesia, less anesthetic required for muscle relaxation so patients recover quickly and completely after surgery.