Feprosidnine (Sydnophen) is a stimulant drug which was developed in the USSR in the 1970s. It is structurally related to another Russian drug mesocarb but unlike mesocarb it has not been developed for medical use in humans.
Sydnophen has multiple mechanisms of action, the relative importance of which has not been clearly established. Effects on the body include cholinergic, adrenergic, opioid and nitric oxide donating actions, all of which may contribute to its pharmacological effects to some extent.
Feprosidnine is a mesoionic sydnone imine.