Classification of Chemical-Warfare Agents Toxic chemical warfare agents are divided into 4 major classes: Nerve agents Pulmonary agents Systemic asphyxiants (blood agents) Vesicants (blistering agents) Nerve agents inhibit the enzyme acetylcholinesterase, causing excess cholinergic stimulation and cholinergic crisis (eg, diarrhea, urination, miosis, bronchorrhea, bronchoconstriction, emesis, lacrimation, salivation).