N₂O (Nitrous Oxide): general

N₂O is a colourless, slightly sweet-smelling gas, usually breathed in through a mask or nosepiece [1]. It has been used in medicine since the mid-19th century and remains one of the most widely used anesthetic gases today, given for labour pain, dental work, procedural sedation, and general anesthesia [2][1]. It is also classed as a short-acting sedative [1].

Two things matter before anything else.

1. N₂O is the least potent inhalational anesthetic used in medicine, and reaching a full anesthetic effect on N₂O alone would require a concentration of 104%, which is not achievable [2]. For general anesthesia it cannot serve as the sole agent and is often combined with a more potent, volatile anesthetic [2].

2. Outside medical and industrial settings, nobody has good numbers on this. How many people use N₂O non-medically, and how often, is not known [3]. What data exists suggests non-medical use is most common among adolescents and young adults, and appears to be rising in some countries [3].

N₂O has a long paper trail — first made in 1772 by Joseph Priestley, who called it "dephlogisticated nitrous air" [4]; named "laughing gas" by Humphry Davy in 1799, who also identified its pain-relieving effect and predicted its surgical use [5]. It is manufactured and sold both as a medical gas under various trade names [3] and for industrial purposes — food processing, semiconductor manufacture, spectrometry, and as an engine additive — in canisters, bulbs, and cylinders of varying sizes [3][5].

References

1. Nitrous Oxide (Laughing Gas): Uses, Side Effects & Safety — Cleveland Clinic
2. Nitrous Oxide - StatPearls - NCBI Bookshelf — NCBI (StatPearls)
3. Nitrous oxide - Expert Committee on Drug Dependence Information Repository — WHO (ECDD)
4. Nitrous oxide — Wikipedia
5. Advances in Understanding the Actions of Nitrous Oxide — PMC (National Institutes of Health)