5 things that can contaminate a lie detector test results

Jul 30, 2022 | News & Science, Polygraph Examiner

Google ‘lie detector test’ and one of the first results that comes up is how to beat a polygraph test. The truth is that when a polygraph test is carried out by a professional examiner, who knows how to carry out the test, without letting any bias contaminate the results, it is near impossible to beat. That being said, there are several factors that can influence a polygraph test so if you’re looking to find accurate answers, keep an eye out for these!


The term ‘lie detector’ is a bit misleading. It would be more accurate to call a polygraph test a ‘deception detector’.
Say you’ve been involved in a crime as an innocent bystander who happened to witness events. The police may ask you to take a polygraph test to eliminate you from the list of suspects. However, while you may be innocent, if you’re holding something back from the police, protecting someone or generally feeling guilty about the events and wishing you’d stepped in earlier, this could alter the results of the polygraph test as it will pick up on your guilt.

It’s natural to feel a bit nervous when going in for a polygraph test but this shouldn’t affect the results: your deception will go up and down if you’re lying to certain questions, while your nervousness won’t be picked up by the machine as much.

Drugs and Medication

Certain drugs and medications can affect how your body responds, or is unresponsive, to guilt and polygraph examinations. Examples include:

  • Anti-hypertensive medication. These are drugs that can alter your blood pressure and heart rate, usually lowering both. The polygraph test detects small changes in these to detect deception, however if your medication is altering the normal rates then results could come back as inconclusive.
  • Anti-anxiety medications. Similar to the above, if these medications alter your emotional state and keep your heart rates and blood pressure low, this could make it much harder for the polygraph test to detect minute changes.
  • Illegal substances. Some drugs may have the same effect as the above medications, lowering both blood pressure and heart rate, but in most cases examiners will be able to tell if you’re intoxicated by these before the test begins.

Tell the examiner about these before you begin and ask if you should wait until you’re medication free to be tested. With the exception of the illegal substances however both of the other medications tend to be prescribed for long term or chronic conditions. A proficient examiner should be able to take the readings to the dummy questions and calibrate the machine accurately to reflect this bias.

Unprofessional Examiners

A good examiner won’t allow any bias to enter the polygraph test. It should be professional and objective, neither making you feel too comfortable or guilty. You’ve no reason to fear the polygraph examiner, if they’re a professional who has been trained properly and is qualified to use the machine you know you’re in good hands.
Pick a professional examiner when you’re looking for a professional polygraph test: if they’re offering to do the test from their home that’s usually a bad sign. They should explain to you about the machine, how it works and what will happen during the test. If you’re unsure or suspicious about your examiner this could affect results. A good polygraph examiner will always behave in a transparent manner.

Test Environment

Again, this is really down to how professional the examiner is. If you’re sitting in an uncomfortable chair, feeling cold and like you’re under interrogation, this can result in inconclusive results.
You should tell the examiner what’s bothering you about the environment or room you’re in, whether it’s a bad smell, a draft on the back of your neck or any worries about the test. If they’re a professional they will make sure that you’re in a clean, quiet environment where you won’t be disturbed. You should feel confident in the examiner by the time the test is about to start.

Mental Illness

A polygraph test will use both physical and emotional indications to detect deceit, but when a person is suffering a mental illness, this can sometimes alter the results. Serious mental health conditions such as paranoid and delusional disorders like schizophrenia can interfere greatly with the test.

Any condition that alters someone’s perception will have abnormal polygraph test results that can’t be relied upon. A professional polygraph examiner should be able to detect that there is an underlying mental illness that could prevent the test from being inconclusive or unethical to conduct.

Polygraph tests can be very effective tools for police work and general deceit detection. When a professional polygraph examiner uses the test correctly, the results can be incredibly accurate, despite the 5 above factors that can sometimes in poor test conditions and contaminate the results.

Copyright 2022 © All rights reserved LIE DETECTOR TEST UK

Regional offices and discreet controlled locations across the United Kingdom