Can a polygraph be “cheated”: an expert’s explanation

3 November 2025 19:34

In the process of preparing for polygraph testing, people resort to various methods of distorting the results of the interview. However, all these methods have weaknesses, and an experienced polygraphologist will detect them. Volodymyr Vedmid, Chairman of the National Association of Polygraphologists of Ukraine, told about it in an interview to the YouTube channel "Komersant Ukrainian".

According to him, there are three methods of countering the polygraph: mechanical, chemical (medication) and psychological.

Mechanical techniques are the most primitive, says the specialist.

“There are sensors built into the polygraph chair. Every movement of a person is recorded – this is, for example, finger tapping, foot tapping and the like. This method of counteraction is the easiest to detect,” Vedmid specified.

Chemical counteraction is the use of various medications or chemicals to distort the test results, the specialist continued.

“Medications come in two types of action: sedatives that make the respondent too relaxed, or various energizers or drugs that make a person overactive,” he explained.

People also often resort to psychological ways of counteracting – for example, depriving themselves of sleep for long periods of time.

“In my practice there were people who before polygraph testing did not sleep for several nights in a row. Such people come in and can hardly breathe. Or they don’t visit the restroom for a day. Then they come in and can’t think about anything else – this, of course, distorts the test results,” he said.

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However, according to Medved, an experienced polygraphologist will easily detect any method of counteraction.

“Every polygraph test begins with a stimulus name test, during which the polygraphologist assesses the state of the person – how he reacts to the addressed speech, how adequate he is, how quickly he responds, does not slow down. If during the pre-test we see that the person is not adequate, we do not let him pass further,” he explained.

Thus, the polygraph does not determine the truth or lie in the literal sense. Polygraph equipment only records the body’s reactions to certain questions. And although attempts to mislead the polygraph happen, an experienced polygraph examiner can see everything from body movements to the slightest signs of stress or medication.