Noun
truth serum (countable and uncountable, plural truth serums or truth sera)
(informal, medicine) A psychoactive medication, especially one administered by injection, which supposedly renders a person cooperative and disposed to respond honestly to questions.
Separate tests of THC as a truth serum were equally unsuccessful. Source: Internet
She sends for Snape, demanding that he provide the magical truth serum Veritaserum in order to force Harry to reveal any information he may be hiding. Source: Internet