Lexorin was a drug utilized during the late 23rd century.
It was able to alleviate symptoms of malaise and/or multiple personality disorder in those who experienced a Vulcan mind meld, or who carried a Vulcan katra prior to its placement on Mount Seleya.
In 2285, James T. Kirk administered a dose of lexorin to Leonard McCoy to help him feel well enough to travel with Spock's katra to Vulcan. (Star Trek III: The Search for Spock)