Deliriants are a class of hallucinogen. The term was introduced by David F. Duncan and Robert S. Gold to distinguish these drugs from psychedelics and dissociatives, such as LSD and ketamine respectively, due to their primary effect of causing delirium, as opposed to the more lucid states produced by other hallucinogens (psychedelics and dissociatives). The term is generally used to refer to anticholinergic drugs.