The vasoconstrictor was a medical tool used to ease inflammation, by reducing blood flow in the relevant vessels.

In 2373, The Doctor used a vasoconstrictor to treat B'Elanna Torres' headache. (VOY: "The Swarm")

According to the call sheet for the second day of filming on VOY: "Scientific Method", Wednesday 30 July 1997, a vasoconstrictor was also used in the scene on the bridge in which a crewmember dies. However, no such tool was visible in this scene.