Perhaps it's important to dust off your copy of The Bill of Rights and re-read the 5th amendment which explicitly states that: "No person shall be nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law..." See: <http://www.nara.gov/exhall/charters/billrights/billrights.html>
However, this means that IF you have due process, then a person CAN be compelled to be a witness against himself, and be deprived of life, liberty and property. Hence using truth drugs or torture would be perfectly constitutional if due process is used, according to the Fifth Amendment. As a supporter of the Constitution you are now obligated to defend to the death those who would torture prisoners, as long as they first get a judge's approval.