Ignoring the whole philosophical issue of what is truth, is there anyway to force someone to tell the truth about something?
This is a pretty common plot device in a wide range of genres. From veritaserum in Harry Potter, to creatures crawling in your brain in Star Trek, to injected drugs in spy movies, it seems that we really want to know that something is available that will help us get to the truth, particularly when we talk to our enemies. But its reality is much less glamorous and reliable.
You can’t make someone tell the truth. But you can potentially reduce their inhibitions so that they are less likely to question why they shouldn’t tell you the truth. Unfortunately, it appears that it also makes a person less likely to question why they shouldn’t make up a story that they think you want to hear. This obviously leads to a high potential for false confessions, which is why confessions under the influence of drugs like sodium pentothol aren’t admissable in court in most countries.
However, these drugs were used by psychiatrists to help patients speak freely about traumatic events, such as war. Unfortunately, it could also be misused to convince patients to create stories to meet what they perceived as the expectations of their physician. There was also a high potential for addiction if misused or mismanaged.
Now, of course, there is also no scientific evidence that you can consume something that will make you lucky. So perhaps, as a muggle I just don’t understand the magic of veritaserum. But, the star trek creatures, and the spy truth serum, they just aren’t possible.
See this interview in Scientific American for more of the history of truth serum.