Narco test involves the injection of a drug, sodium pentothal, which induces a hypnotic or sedated state in which the subject’s imagination is neutralised, and they are expected to divulge true information.
The drug, referred to as “truth serum” in this context, was used in larger doses as anaesthesia during surgery, and is said to have been used during World War II for intelligence operations.
Different from Narco test, polygraph test is based on the assumption that physiological responses that are triggered when a person is lying are different from what they would be otherwise.
In Selvi & Ors vs State of Karnataka & Anr (2010), a Supreme Court ruled that no lie detector tests should be administered “except on the basis of consent of the accused”.
The court took into consideration international norms on human rights, the right to a fair trial, and the right against self-incrimination under Article 20(3) of the Constitution.