WordReference Random House Unabridged Dictionary of American English © 2020
truth se′rum, 
  • Drugsa drug, as the barbiturate thiopental, that induces in the subject a desire to talk or a state of heightened suggestibility, used in psychotherapy and in interrogation to discover repressed or consciously withheld information.
  • Also,  truth drug′. Cf.  narcoanalysis. 
    • 1920–25

    Collins Concise English Dictionary © HarperCollins Publishers::
    truth drug, truth serum n
    1. informal any of various drugs supposed to have the property of making people tell the truth, as by relaxing them
    'truth serum' also found in these entries (note: many are not synonyms or translations):
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