Deliritants are a category of hallucinogens that are sometimes referred to as true hallucinogens, since they evoke hallucinations in the proper connotation of the word; people may have conversations with beings or things that do not exists and have no basis in reality, or they may be completely unaware they are talking to themselves in the mirror, and they may have no recollection of certain events at all.

Deliritants are antagonists of the acetlycholine receptors.

Deliritants differ from other hallucinogens because they cause true hallucinations. For this reason they can also be more dangerous. Many of the tropane alkaloids found in the plants listed below are toxic and can cause death in high doses, which is not true for many psychedelics and dissociatives.

Systematics:
Roughly fall into two broad categories: tropane alkaloids and deliriant antihistamines.

Tropane alkaloids: atropine, hyoscyamine and scopolamine. Found in plants of Solanaceae family (Nightshades), Datura spp., Mandragora (Mandrake), Atropa (most notably Atropa Belladonna, the Deadly Nightshade) and Henbane (Hyoscyamus niger).

Deliriant antihistamines: most notably diphenhydramine and dimenhydrinate.

Benzydamine (Benalgin, Tantum Rosa, etc.): should probably be placed in a distinct subset because it's neither tropane nor antihistamine. Even though it manifests many side-effects of anticholinergics, it is also distinctly different and produces a different delirium with less (or none) confusion, disorientation or illogical thinking. Although it produces many true hallucinations (visual, auditory and tactile), there are also many easily recognised as hallucinations (resembling more effects of psychedelics). For the most part of the trip subject is fully aware and moments of being startled and scared by true hallucinations are rare.

RS. Turnbull "Benzydamine Hydrochloride (Tantum) in the management of oral inflammatory conditions."
"Benzydamine HCL (Tantum) is a topical nonsteroidal anti-inflammatory drug (NSAID) with anti-inflammatory, analgesic, antipyretic and local anesthetic activity. This paper reviews the pharmacology of benzydamine and surveys the existing literature relating to its applications in medicine and dentistry."

Opaleye ES, Noto AR, Sanchez ZM, Moura YG, Galduróz JC, Carlini EA."Recreational use of benzydamine as a hallucinogen among street youth in Brazil."

See: Psychedelics v.s. dissociatives v.s. deliriants