A variety of ion channel blockers (inorganic and organic molecules) can modulate ion channel activity and conductance.
Some commonly used blockers include:
* Tetrodotoxin (TTX), used by puffer fish and some types of newts for defense.  It blocks sodium channels.
* Saxitoxin is produced by a dinoflagellate also known as "red tide".  It blocks voltage-dependent sodium channels.
* Conotoxin is used by cone snails to hunt prey.
* Lidocaine and novocaine belong to a class of local anesthetics which block sodium ion channels.
* Dendrotoxin is produced by mamba snakes, and blocks potassium channels.
* Iberiotoxin is produced by the Hottentotta tamulus (Eastern Indian scorpion) and blocks potassium channels.
* Heteropodatoxin is produced by Heteropoda venatoria (brown huntsman spider or laya) and blocks potassium channels.