Inhalants are a broad range of drugs whose volatile vapors are taken in via the nose and trachea. They are taken by volatilization, and do not include drugs that are sniffed after burning or heating. For example, amyl nitrite and toluene are considered inhalants, but tobacco, marijuana, and crack are not.
While some inhalant drugs are used for medical purposes, as in the case of nitrous oxide (a dental anxiolytic), this article focuses on inhalant abuse as recreational drugs that are used for their intoxicating effect. Inhaling volatile substances because of their intoxicating effect is called huffing.
Read more about Inhalants: Classification, Inhalant Users, Administration and Effects, Dangers and Health Problems, "Sudden Sniffing Death", Socioeconomic Factors