Neurozine was an anesthetic that was used during the late 24th century and that could be dispensed in gaseous 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")