Adamsite, also known as DM (diphenylaminearsine), is a riot control agent that serves to temporarily incapacitate those exposed. It is relatively safe due to a high LCt50* (11,000 mg/min/m³) and low effective Ct50. The effects are short lived (several hours) once the agent is removed; however, it is longer lasting than other lacrimating agents.

Riot control agents are not considered chemical warfare agents as defined by the Geneva Convention of 1925, and they are utilized by police forces worldwide.

DM is a yellow-green, odorless, crystalline solid. It is disseminated as a smoke or aerosol mist via spray can, tank, grenade, or larger bombs. DM is considered a vomiting agent, although at normal field use concentrations, it initially produces eye and mucosal irritation and violent coughing. It tends to produce less skin irritation than the other riot control agents do. At higher concentrations or after prolonged exposure, it produces severe headache, malaise, nausea, vomiting, abdominal cramping, and diarrhea. Symptoms may last for 1-2 hours. The time to onset of symptoms following exposure is usually several minutes, which is much longer than other riot control agents and usually leads to longer exposure and more severe symptoms (eg, headache, nausea, and vomiting). Thus, by the time the patient experiences warning properties, significant exposure has likely occurred.

*LCt50 (L = lethal, C = concentration of vapor [mg/m³], t = exposure time [minutes]) is the concentration of a chemical agent exposure by inhalation that causes death in 50% of unprotected people.