The US justice department told the CIA in 2002 that its agents would not be prosecuted for carrying out harsh interrogations if they believed they would not cause "prolonged mental harm", according to a memo written by a senior official.
The memo, released on Thursday by a civil rights group, approved the CIA's harsh interrogation techniques method by method.
The August 1, 2002 legal opinion, signed by Jay Bybee, the then assistant attorney-general, was obtained by the American Civil Liberties Union along with other documents.
The heavily censored document specifically approved proposed interrogation techniques that were devised for use against al-Qaeda suspects who were resistant to other questioning methods.
However, it also warned that if circumstances changed, interrogators could be prosecuted under anti-torture laws.
The standards used to judge how physically rough an interrogation was were censored.
"The healthier the individual, the less likely that the use of any one procedure or set of procedures will result in prolonged mental harm."
The memo suggested psychiatrists or psychologists should be consulted prior to interrogations to assess the likely mental health effect on the prisoner.
"The healthier the individual, the less likely that the use of any one procedure or set of procedures will result in prolonged mental harm," the memo stated.
Bybee wrote the memo the same day he wrote one for Alberto Gonzales, the then-White House counsel, that defined torture as only those "extreme acts" that cause pain similar in intensity to that caused by death or organ failure.
The Bybee legal opinion defining torture was withdrawn more than two years later.
More at the news organization that Republicans love to hate Al Jazeera.