Indian police use truth serum to find clues in cases
India's Supreme Court has said that the use of a "truth drug" by police in questioning suspects is illegal and a violation of their fundamental rights.
The court said a suspect's consent was required to do the test and even then it could not be treated as evidence.
"Truth drug" test results have never been admissible in Indian courts but police say they have provided leads.
Correspondents say the ruling effectively means the police will no longer be able to do such tests.
"Narco, brain mapping and polygraph tests are illegal and a violation of personal liberty," a three-judge bench headed by Chief Justice KG Balakrishnan ruled.
The court's order came in response to petitions filed by several accused questioning the validity of such tests.
In the tests, a suspect is injected with sodium penthanol, a chemical that numbs powers of perception and supposedly makes it difficult for a person to lie during questioning.
The test results were never admissible in court as evidence, but police often made suspects take the tests in order to get "vital clues" in a case, correspondents say.
Such tests were conducted on Maoist leader Kobad Ghandy who was arrested last year.
They were also performed on two men accused of killing 17 young women and children in Noida, a suburb of the Indian capital, Delhi.