Lexorin
From Star Trek : Freedom's Wiki
Lexorin is a drug utilized during the late 23rd century that was developed to alleviate symptoms of malaise and/or multiple personality disorder in those who experience a Vulcan mind meld, or who carry a Vulcan katra prior to its placement on Mount Seleya.
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)
