Pentathnol

Pentathnol (also known as truth dope) was a type of drug that was used in the 23rd century to induce narcosynthesis in a patient.

In 2266, Captain James T. Kirk wanted Dr. Leonard H. McCoy to give Professor Robert Crater a dose of pentathnol so that he could interogate him, and identify what Crater knew about the M-113 creature. (TOS novelization: "The Unreal McCoy").