Neurozine
From Star Trek : Freedom's Wiki
Neurozine is an anesthetic that was used during the late 24th century that can be dispensed in a gas form. In 2374, neurozine, axonol and anesthezine were considered to be "only the best."
That year, the Doctor and EMH Mark II used three canisters of neurozine gas, distributed through the ventilation system, to incapacitate the Romulans who had hijacked the USS Prometheus. (VOY: "Message in a Bottle")
