Riot-control agents are compounds that were initially developed for crowd control but that have also been used in military conflicts (see also Overview of Chemical-Warfare Agents). Riot-control agents are also referred to as harassing agents, tear agents, or lacrimators and are often incorrectly called tear gas, but in fact they do not exist as gases or vapors. Instead, they are solids that can be dispersed as liquids (by dissolving the solid agent to form a solution and then spraying the solution) or as aerosols (small particles released explosively or as smoke). Like anticholinergic agents, they are intended to cause incapacitation rather than serious injury or death, although deaths due to pulmonary edema (acute lung injury) have occurred.
Military versions of these agents include chloroacetophenone (CN, also marketed as Mace#174;), chlorobenzylidenemalononitrile (CS), dibenzoxazepine (CR), and diphenylaminoarsine (adamsite, or DM, a so-called vomiting agent). Oleoresin capsicum (OC, pepper spray) is a more recently developed riot-control agent used primarily for law enforcement and personal protection. Chloropicrin (PS) is a compound used during World War I that is occasionally regarded as a riot-control agent, although it is more properly classified as a pulmonary agent.