Most venomous lizard

Based upon current research results, the world's most venomous lizard is the Gila monster (Heloderma suspectum) native to south-west USA and north-west Mexico. LD50 (lethal dose) values for its venom as low as 0.4 mg/kg have been recorded when administered intravenously in mice. This is comparable to the toxicity of the venom of the western diamondback rattlesnake (Crotalus atrox). Human deaths from Gila monsters are few, because only relatively small amounts of venom are delivered as the lizards have to "chew" the venom in as they lack the hollow, syringe-like fangs of venomous snakes.

LD50 values as low as 1.4 mg/kg have been recorded in the Gila monster's only close-living relative, the Mexican beaded lizard (H. horridum).

For many years, these two species were believed to be the world's only venomous lizards alive today, but in recent times scientists have been surprised to discover that several species of monitor lizard and iguana are also venomous, including the largest living lizard, the Komodo dragon (Varanus komodoensis), of Indonesia.