Lethozine is a neurochemical isolator.
Lethozine can be used with metrazene to reduce the physiological response in the body of an individual who has been joined with a Trill symbiont. (ST - Divided We Fall comic: "All Fall Down", ST reference: The Starfleet Survival Guide)
In 2376, Julian Bashir used lethozine, metrazene and metraprovoline when Ezri Dax started to reject the Dax symbiont after an encounter with the "cathedral artifact" in the Gamma Quadrant. (DS9 - Mission Gamma novel: Cathedral)