This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
Muscarine is found in the Fly Agaric, Amanita muscaria, a poisonous mushroom, used in Homeopathic practice under the name, Agaricus muscarius, but largely abandoned by them as a remedy. Agar-icin, derived from it, is a very uncertain and unreliable agent. Muscarine nitrate, in doses of 1-30 to 1-15 grain, has been employed in the treatment of night sweats and in diabetes insipidus. Such use is not to be commended. Synthetic muscarine is a nitrous ester of choline, with a curare-like action. It is about one-tenth as toxic as muscarine, but it should not be used in therapeutics.
Muscarine influences involuntary muscle in the same way but to a greater degree than pilocarpine, but affects the secretory glands to a less degree. Muscarine inhibits heart action by stimulating the vagus nerve-endings. It is antagonized by atropine.