If people are willing to swear that they will tell the truth and nothing but, then there is no reason not to go ahead and use truth serum. However, it should ultimately be each person's right to decide if they will submit to using truth serum or not, though if they refuse then it is clear they probably will not be telling the entire truth in the first place, which will be just as well.
I would say yes to this question, if only we didn't have that pesky thing known as the fifth amendment. A person cannot be compelled to testify against themselves, unless it is of their own free will. Using a truth serum or otherwise compelling a confession runs afoul of the constitution.
In the United States, there is a constitutional right against self incrimination. Defendants should not be forced to testify against themselves under the influence of a "truth serum". There are certainly many ways in which the process could be abused. Additionally, dosing a person against their will or under coercion is a violation of bodily integrity.
A person under trial who is suspected of being guilty has not yet been convicted, therefore they are still innocent. No innocent person should have their body violated with a drug against their will. Furthermore, this infringes upon an individual's fifth amendment right to not be "compelled in any criminal case to be a witness against himself". It is simply unconstitutional.
In our legal system one constitutionally has the right to be defended on the absolute facts as they appear. When a foriegn agent is entered into one's body there is no scientific explanation whether the person is stating a fact or being manipulated by the questioner. When the courts and the pharmaceutals act in concert to be invovled with the trial it is constituionally wrong