Theoretically, by drinking small amounts of truth serum over a long period of time, you could build up an immunity to it. Therefore, drinking a whole lot of it all at once should work even better.
(In-game plural: vials of interrogative elixir)
Playing Bastille Battalion with Truth Serum in the Moat
|You drink the vial of interrogative elixir... or did you?|
|TOP 10 interrogative elixir collections|
6. Princess Erin - 2 | 7. Pumpkinheadme - 2 | 8. Terrapin_Man - 2 | 9. runeslayer - 1 | 10. THE Duke of Doi Tung - 1
Collection data courtesy of ePeterso2 and Jicken Wings