Inhalants

The one family on this tree grouped by route rather than mechanism, and grouped that way deliberately: what is inhaled from a rag, a bag or a bottle shares a risk profile its pharmacology does not predict. Mechanistically the members have almost nothing in common. The alkyl nitrites — amyl, isobutyl and isopropyl — are smooth-muscle vasodilators that release nitric oxide and can oxidise haemoglobin to methaemoglobin. The volatile solvents and gases, toluene, butane, 1,1-difluoroethane and chloroform, are non-specific CNS depressants.

The route-level fact is sudden sniffing death syndrome (SSDS): hydrocarbons and fluorocarbons sensitise the myocardium to adrenaline, so a startle or a run during use can trigger a fatal arrhythmia in someone with no prior warning. Displaced oxygen adds asphyxia on top of it. Nitrites are separately fatal with PDE5 inhibitors. N₂O is inhaled too, but it is an NMDA antagonist and is filed under Dissociatives — route is not a class.