Truth Serum: The Basics
The Truth Serum is a drug that is used exclusively by Candor in upholding their virtue of honesty. The serum is used mainly for Candor initiation and interrogation.

It has been mentioned by Christina that when she was growing up in Candor, they gave her the truth serum which forced her to share all of her deepest secrets in front of the entire faction.
Truth Serum: Books to Film
In Insurgent, the Truth Serum was visibly used for the first time on Four and eventually on Tris upon arriving in Candor for the first time. Jack Kang, Candor's leader, ordered the two be arrested and interrogated for allegedly committing crimes against humanity after seeing Four running the Attack Simulation and seeing Tris supposed help him. Jack ordered the two to be interrogated in front of the entire Candor population.

Their interrogator was a Candor man named Niles. He injected a needle containing the truth serum into Four's neck. They asked him for his name, in which he said "Four." Due to that not being his real name, they asked for his real name, in which he eventually said Tobias Eaton (though after a lot of resistance against the serum). After realizing that Four is the son of Marcus Eaton, they asked him if the rumors about his father's abuse was true. Four tried his best to resist the serum, but in the end, he eventually confirmed the rumors when Niles asked him why he switched to Dauntless and Four responded with, "Because I wanted to escape my father."

After Four, Tris was next to be interrogated. However, instead of Niles plunging the serum into her neck, she wanted to do it herself. Her reasoning behind it was because it gave her a sense of control. Niles asked for her name to which she responded with "Beatrice Prior." Eventually, Niles started questions her about what her role was related to the attack simulation. She was acquitted as well when they found out that she was in the Dauntless control room only to try to stop Four and the simulation itself. However, by the end of it, she was forced to tell everyone that she was the one her killed Will when Niles asked her what her greatest regret and biggest secret was. At the end of Tris' interrogation, the Candor said the same thing as they said to Four, "Thank you for your honesty."


 
Truth Serum: The Effects
The Truth Serum, as its name suggests, puts the person administered with it under a lethargic effect that makes them willingly answer questions without much struggle. Upon being administered the serum, Tris forgot why she was being asked questions, adding to the powerful effects of the serum.

It is said by Christina that no one is able successfully deny answering any question while under the Truth Serum. However, due to the special nature of the Divergent, Tris was able to keep the answer from leaving her when under the serum. It can be concluded that those who are Divergent are able to, with enough effort, resist the effects of the Truth Serum.

Not many Divergents or Genetically Pures are seen completely resisting truth serum to the point where it doesn’t work at all (Nita when about to inject David), only Tris in recent memory (said by Matthew). But Tris can still feel the weighing effects of the Truth Serum.
Coded by Serena Addams