Pain-relieving compounds as strong as morphine have been extracted from the venom of the black mamba, one of the world's deadliest snakes.
Injecting the chemicals, called mambalgins, into mice produced powerful pain relief without serious side effects.
The protein building blocks, or peptides, act on acid-sensing ion channels (Asics) which control the passage of electricity across cell membranes.
Ion channels play a key role in the nervous system and are often targeted by the venom of poisonous snakes, spiders and fish.
Mambalgins shut down Asics, which are specific to sensory neurons to block pain signals.
The scientists led by Anne Baron, from the Institute of Molecular and Cellular Pharmacology in Valbonne, France, wrote in the journal Nature: "It is essential to understand pain better to develop new analgesics.
"The black mamba peptides discovered here have the potential to address both of these aims.
"They show a potent role for different Asic subtypes in both the central and peripheral pain pathways, providing promising new targets for therapeutic interventions against pain, and they are themselves powerful, naturally occurring, analgesic peptides of potential therapeutic value."