Nitrous oxide (N2O) is a colourless gas discovered by Joseph Priestly in 1772. In human and veterinary medicine, it is used with oxygen as an anaesthesia due to its pain-relieving effects. It is often referred to as ‘laughing gas’ because it can give those who inhale it a euphoric mood. Other legitimate uses of nitrous oxide include as a fuel additive and as an approved food additive when used as a propellant for whipped cream.

Recreational users typically inhale via a balloon inflated with the gas. There are health risks associated with the recreational use of nitrous oxide.