Recreational use of nitrous oxide
Nitrous oxide (N2O), commonly referred to as laughing gas, along with various street names, is an inert gas which can induce euphoria, dissociation, hallucinogenic states of mind, and relaxation when inhaled. Nitrous oxide has no acute biochemical or cellular toxicity and is not metabolized in humans or other mammals.
Source: Wikipedia — Recreational use of nitrous oxide (CC BY-SA 4.0)