Atropine is a naturally occurring tropane alkaloid
Tropane alkaloid
Tropane alkaloids are a class of alkaloids and secondary metabolites that contain a tropane ring in their chemical structure...

 extracted from deadly nightshade
Deadly nightshade
Atropa belladonna or Atropa bella-donna, commonly known as Belladonna, Devil's Berries, Death Cherries or Deadly Nightshade, is a perennial herbaceous plant in the family Solanaceae, native to Europe, North Africa, and Western Asia. The foliage and berries are extremely toxic, containing tropane...

 (Atropa belladonna), Jimson weed
Datura stramonium
Datura stramonium, known by the common names Jimson weed, devil's trumpet, devil's weed, thorn apple, tolguacha, Jamestown weed, stinkweed, locoweed, datura, pricklyburr, devil's cucumber, Hell's Bells, moonflower and, in South Africa, malpitte and mad seeds, is a common weed in the...

 (Datura stramonium), mandrake
Mandrake (plant)
Mandrake is the common name for members of the plant genus Mandragora, particularly the species Mandragora officinarum, belonging to the nightshades family...

 (Mandragora officinarum) and other plants of the family Solanaceae
Solanaceae are a family of flowering plants that include a number of important agricultural crops as well as many toxic plants. The name of the family comes from the Latin Solanum "the nightshade plant", but the further etymology of that word is unclear...

. It is a secondary metabolite
Secondary metabolite
Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolities does not result in immediate death, but rather in long-term impairment of the organism's...

 of these plants and serves as a drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

 with a wide variety of effects. It is a competitive antagonist
Competitive antagonist
A competitive antagonist is a receptor antagonist that binds to a receptor but does not activate the receptor. The antagonist will compete with available agonist for receptor binding sites on the same receptor...

 for the muscarinic acetylcholine receptor
Muscarinic acetylcholine receptor
Muscarinic receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled in the plasma membranes of certain neurons and other cells...

. It is classified as an anticholinergic drug (parasympatholytic
A parasympatholytic agent is a substance or activity that reduces the activity of the parasympathetic nervous system. A parasympatholytic agent is a substance or activity that reduces the activity of the parasympathetic nervous system. A parasympatholytic agent is a substance or activity that...

). The species name "belladonna" comes from the original use of deadly nightshade as a way of dilating women's pupils to make them beautiful.