A stimulant that Leonard McCoy passes off as vitamin shots to the Kelvan Hanar, making him irritable and argumentative as part of the plan to retake the Enterprise.
Formazine is a drug used in the Original Series episode By Any Other Name. The Kelvans who seize the Enterprise have taken human form, and Kirk realises that their unfamiliar bodies leave them open to every human sensation and emotion.
Each senior officer picks a target. McCoy examines the Kelvan Hanar, declares him run down and prescribes a course of vitamin injections; the hypospray actually contains formazine, a stimulant that in repeated doses leaves the patient tense, short-tempered and quarrelsome.
Hanar is soon snapping at his commander Rojan, adding to the disorder caused by Scott's drinking contest with Tomar and Kirk's attentions to Kelinda. Together the provocations break the Kelvans' discipline and persuade Rojan to negotiate.