Neuromuscular blocking drugs are often classified into two broad classes:
*Pachycurares, which are bulky molecules with nondepolarizing activity
*Leptocurares, which are thin and flexible molecules that tend to have depolarizing activity.
It is also common to classify them based on their chemical structure.
*Acetylcholine, suxamethonium, and decamethonium
Suxamethonium was synthesised by connecting two acetylcholine molecules and has  the same number of heavy atoms between methonium heads as decamethonium.  Just like acetylcholine, succinylcholine, decamethonium and other polymethylene chains, of the appropriate length and with two methonium, heads have small trimethyl onium heads and flexible links. They all exhibit a depolarizing block. 
* Aminosteroids
Pancuronium, vecuronium, rocuronium, rapacuronium, dacuronium, malouètine, dihydrochandonium, dipyrandium, pipecuronium, chandonium (HS-310), HS-342 and other HS- compounds are aminosteroidal agents. They have in  common the steroid structural base, which provides a rigid and bulky body. Most of the agents in this category would also be classified as non-depolarizing.
* Tetrahydroisoquinoline derivatives
Compounds based on the tetrahydroisoquinoline moiety such as atracurium, mivacurium, and doxacurium would fall in this category. They have a long and flexible chain between the onium heads, except for the double bond of mivacurium. D-tubocurarine and dimethyltubocurarine are also in this category. Most of the agents in this category would be classified as non-depolarizing.
* Gallamine and other chemical classes
Gallamine is a trisquaternary ether with three ethonium heads attached to a phenyl ring through an ether linkage. Many other different structures have been used for their muscle relaxant effect such as alcuronium (alloferin), anatruxonium, diadonium, fazadinium (AH8165) and tropeinium.
*Novel NMB agents
In recent years much research has been devoted to new types of quaternary ammonium muscle relaxants. These are asymmetrical diester isoquinolinium compounds and bis-benzyltropinium compounds that are bistropinium salts of various diacids.  These classes have been developed to create muscle relaxants that are faster and shorter acting. Both the asymmetric structure of diester isoquinolinium compounds and the acyloxylated benzyl groups on the bisbenzyltropiniums destabilizes them and can lead to spontaneous breakdown and therefore possibly a shorter duration of action.