Scopolamine

Structurally similar to the nerve substance acetylcholine, a chemical released to trigger nerve impulses. This substance therefore competes with acetylcholine thus interfering with the transmission of nerve impulses in the parasympathetic nervous system and produces symptoms typical of parasympathetic system depression. These symptoms include dilated pupils, rapid heartbeat, and dry skin, mouth, and respiratory passages. As scopolamine depresses the central nervous system, it is used as a sedative prior to anesthesia and as an antispasmodic in certain disorders characterized by restlessness and agitation. Overdosage of scopolamine causes delirium, delusions, paralysis, and stupor.

Found in many of the nightshade species.