Anticholinergic agents, and particularly scopolamine, have long been known to decrease opioid-related nausea and vomiting, although their narrow therapeutic range and inconvenient route of administration (typically transdermal) has limited their application. Anticholinergic agents are thought to act via inhibition of muscarinic receptors in several regions of the medulla oblongata, which are implicated with nausea and vomiting generation; in addition to the chemoceptor trigger zone, these receptors are particularly concentrated in, but not limited to the nucleus tractus solitarius. Cholinergic receptors have been typically associated with motion sickness, but cholinergic agonists such as neostigmine have been shown to increase the incidence of PONV, especially when injected intrathecally.