Humans have known since the time of the Roman Empire that we're more readily truthful while under the influence. That's where the idea behind the term "truth serum" comes from. Truth serum refers to a number of mind-altering drugs that are supposed to make you incapable of lying, but the reality is no drug is powerful enough to grip the human mind so tightly as to make it impossible to lie. Some truth serums, like sodium thiopental, slow the speed at which your body sends messages from your spinal cord to your brain. As a result, it's more difficult to...