Scopolamine acts by interfering with the transmission of nerve impulses by acetylcholine in the parasympathetic nervous system (specifically the vomiting center).
Scopolamine is a muscarinic antagonist structurally similar to the neurotransmitter acetylcholine and acts by blocking the muscarinic acetylcholine receptors and is thus classified as an anticholinergic. Scopolamine has many uses including the prevention of motion sickness. It is not clear how Scopolamine prevents nausea and vomiting due to motion sickness. The vestibular part of the ear is very important for balance. When a person becomes disoriented due to motion, the vestibule sends a signal through nerves to the vomiting center in the brain, and vomiting occurs. Acetylcholine is a chemical that nerves use to transmit messages to each other. It is believe that Scopolamine prevents communication between the nerves of the vestibule and the vomiting center in the brain by blocking the action of acetylcholine. Scopolamine also may work directly on the vomiting center. Scopolamine must be taken before the onset of motion sickness to be effective.
1. Putcha L, Cintron NM, Tsui J, Vanderploeg JM, Kramer WG: Pharmacokinetics and oral bioavailability of scopolamine in normal subjects. Pharm Res. 1989 Jun;6(6):481-5.