Axonol was a sedative medicine used by the Federation and Starfleet. One use was for psychiatric patients. It could also be dispersed in gaseous form, as a crowd-control anesthetic.
According to his medical file, Spock's physician recommended that he be treated with axonol, as well as dylamadon, melorazine, tetrovaline, and cortropine, when he had himself admitted to the psychiatric ward of Starbase 5. (DIS: "Point of Light")
On the USS Prometheus, it was one of three agents recommended for use at the behest of the Emergency Medical Hologram Mark II, the other two being anesthezine and neurozine. (VOY: "Message in a Bottle")