truth drug 
noun
A drug supposedly able to induce a state in which a person answers questions truthfully.I'm also going to administer the truth drug here as well, ‘he said touching the tube connected to the man's leg.’...
- If you took a truth drug, what would you be worried about divulging?
- As he explained, it can refer to anything from the use of so-called truth drugs to application of one or another method of torture.