Subject: What is Truth Serum?

Dear Sir/Madame,

 Something has been puzzling me for a while now. I cannot seem to 
grasp the concept of the truth serum. I have difficulty understanding 
how a drug can coerce someone to tell the truth without inflicting 
pain and even if pain was used as means of getting the truth out of 
someone, if the person who does not know the truth (and wants to find 
that out) it does not neccesarily mean that the information that he is 
getting - through inflicting pain- is correct.
 I can understand how drugs can have effect on emotions because 
emotions can be defined in terms of chemicals but lying is not an 
emotion (I think).
 If truth serum is indeed as effective as people claim, why is it not 
applied to every court case or can it be applied? Is their an ethics 
or free will arguement, or financial reason for this?
 I would also like to know if truth serum can tap through the 
unconscious. In other words, let us say that someone is brainwashed or 
suffers from memory loss can truth serum help?
 Thanking you in advance, I remain,

                                               Yours truly,

                                               Mr. A. Peterson

Re: What is Truth Serum?