TRANQUILIZER FOILS LIE-DETECTOR TESTS (Published 1981) (2024)

A small dose of the widely used tranquilizer meprobamate allows people to lie without detection in polygraph, or lie-detector tests, according to a report in the journal Science.

Polygraph instruments are widely used in police investigations and personnel screening. They measure such physical reactions as changes in breathing, heart rate and electrical conductivity of the skin. They depend on the proposition that the person being tested will be under more stress and react more vigorously when trying to deceive than when telling the truth.

But the tests have long been controversial both because of their implied threat to personal privacy and because of specialists' questions concerning their reliability. Critics have questioned whether expert habitual liars can escape detection. Some have also suggested that innocent people might sometimes overreact to stressful questions even while telling the truth. Experts in the testing say the method is reliable even in the face of these circ*mstances.

The new report in the April 3 issue of Science said that normal people outwitted the tests after taking one 400-milligram dose of meprobamate, the widely used minor tranquilizer sold as Miltown and under many other brand names. Furthermore, the people administering the tests were unable to tell who had taken the tranquilizer and who had not. The dose was chosen as the typical minimum that is medically useful. Model for Study of Social Stress

The scientists at the Institute of Pennsylvania Hospital and the University of Pennsylvania said they had been investigating the detection of deception both as a practical problem and as a model for studying social stress. The authors are William M. Waid, Emily Carota Orne, Martin T. Orne and Mary R. Cook.

''One question that is important for both purposes,'' said their report, ''is whether a tranquilizer selectively reduces the physiological response to social stress - in this instance, the stress of attempting to deceive.''

The scientists found that the tranquilizer did reduce that stress but left the person otherwise apparently unchanged. The evidence came from a study involving 44 normal volunteers, male college students 18 to 24 years old. They were all assigned the task of memorizing six words. Then 33 were assigned to a ''guilty'' group and were told to lie when asked about the words on a polygraph test. The other 11, assigned ''innocent'' status, were instructed to tell the truth. Three Groups of 'Guilty' Men

The ''guilty'' men were divided into three groups: one taking the tranquilizer; another taking an ineffective sham pill and the third receiving nothing. The men in the first two groups were told they were being given a tranquilizer to help them deceive the test.

The polygraph testers identified most of the ''guilty'' subjects in the groups who had taken the sham pills or no pills, but most who had taken the tranquilizer were incorrectly identified as innocent.

The results did not stem from a total lack of responsiveness in the tranquilized men, the report said, but from a lack of heightened response when the men were lying.

''It is possible that meprobamate is effective in the experimental laboratory but would be ineffective in the lie-detection laboratory where fear of detection is presumably greater, '' said the report. ''It should be noted, however, that 400-mg doses of meprobamate are effective in reducing the anxiety of psychiatric patients.''

The scientists also said it was possible that substantially higher doses of the drug could be used, without detection, to defeat the polygraph. Several studies have shown that it is possibe to take single doses as high as 800 milligrams with no observable impairment in behavior, the researchers said.

The researchers concluded that their results supported doctors' observations that tranquilizers such as meprobamate did selectively reduce the physiological responses to disturbing events rather than simply reducing overall arousal.