Gases

Gases and volatile agents acting at NMDA receptors: nitrous oxide and xenon, with the anaesthetic vapours sevoflurane and diethyl ether filed beside them. N₂O is here rather than under Inhalants for the reason the taxonomy gives generally — it is inhaled, but route is not a class, and the mechanism is the one ketamine works through.

What varies is that everything here except N₂O is a medical anaesthetic given with oxygen, an airway and monitoring; remove those and the margin being relied on was the setting's, not the drug's. The characteristic harm of this family is not the receptor at all. It is displacement of oxygen — from a mask, a bag or an enclosed space — and unconsciousness reached somewhere falling is dangerous. Sustained heavy nitrous use also inactivates vitamin B12, and the resulting nerve damage can outlast the drug.