Top 10 Reasons for Failing a Polygraph Test (2024)

So you’re scheduled to take a polygraph test soon. Maybe it’s for a new job application, or your partner thinks you’re being dishonest about something. Whatever the reason, you’re probably feeling anxious about it.

Failing a polygraph test can have serious consequences. It could cost you your dream job or relationship. The good news is that, with the right mindset, you can improve your chances of passing. Understanding the most common reasons people fail polygraph tests is the first step.


1. Physiological Responses

A person hooked up to a polygraph machine and a tester in the background.

The polygraph records several of your physiological responses while you answer questions. Things like blood pressure, pulse, respiration, and skin conductivity. When you feel anxious or stressed, these responses can fluctuate.

The examiner compares your responses to baseline levels. Significant changes may indicate deception. But there are many reasons why you may have a strong physiological reaction unrelated to lying.

For example, if you’re very nervous about the test itself, you may exhibit increased vitals even when answering truthfully. Things like having to urinate, feeling too hot or cold, or being uncomfortable in the chair can also alter your physiology.


  • Get a good night’s sleep before the test. Being tired can exacerbate anxious feelings.
  • Avoid caffeine and other stimulants close to the test time. They can increase heart rate and blood pressure.


2. Overthinking Questions

The polygraph examiner will ask you some simple baseline questions first, like “Is your name [your name]?” This establishes your normal responses.

When answering the main questions, people often overthink rather than going with their gut reaction. This causes longer response times and changes in physiology.

For example, say the question is: “Did you steal money from your employer?” If you did not, the immediate response should be no. But you may start thinking “What if they don’t believe me?” This self-doubt can alter your reaction.


  • Don’t try to outsmart the test. Go with your first instinct.
  • Answer questions directly without elaboration. Simply yes or no.
  • Don’t worry about what the examiner may think. Focus on answering honestly.


3. Lack of Clarity

A Man Appealing A Failed Or Inconclusive lie detector Result

Ambiguous or unclear questions can also lead to failed polygraph results. If you’re unsure exactly what the examiner is asking, you may stumble over your response. Or you may make assumptions about the question that are incorrect.

For example, the question “Did you ever steal from work?” seems straightforward. But does this refer only to direct theft? What about using office supplies for personal use or fudging time cards?

Without knowing exactly what theft means in this context, you can’t give a definitive yes or no answer. This confusion will show up in your results.


  • Ask for clarification if a question seems unclear. Don’t guess the meaning.
  • Answer only the question asked, not what you think they meant to ask. Stick to the facts.
  • If a question seems overly broad, ask for specifics about dates, locations, etc.


4. Trying Countermeasures

There are many myths about fooling the polygraph machine through countermeasures. Things like biting your tongue, pressing toes to the floor, or counting backward. Not only are these ineffective, but they can backfire.

Countermeasures require extra focus and can actually heighten your stress responses. The examiner is also trained to notice these physical actions. Getting caught using them is essentially a failed test.


  • Be honest. Don’t try to outsmart the machine or use tricks. They don’t work.
  • Listen carefully and answer calmly. Attempting countermeasures will only raise suspicion.
  • Keep still during the test without extraneous movements. This can alter your results.


5. Disclosing Too Much

An examinee is attached to a lie detector test machine.

Before the official polygraph, the examiner will usually conduct a pre-test interview. This allows them to review the questions and get to know you better. Some candidates think disclosing everything upfront will help “clear the air.”

In reality, offering too much unsolicited information can hurt you. It provides more leads for the examiner to pursue on the actual test. Even if these issues are unrelated, they can alter your frame of mind.


  • Keep responses to interview questions brief and honest without elaborating too much.
  • Don’t mention anything negative about yourself that is not directly relevant to their questions.
  • Be cooperative but don’t feel like you have to tell your whole life story.


6. Lack of Sleep

Being tired affects both your mental clarity and physiological responses. You are more likely to react strongly to questions simply because you’re exhausted.

The night before the polygraph, many people have difficulty sleeping due to anxiety. This compounds the issue further. Arriving to the test already worn out makes it much easier to fail.


  • Try to get at least 8 hours of sleep the night prior to be fully rested.
  • Avoid strenuous activity right before bedtime to improve sleep quality.
  • If you have insomnia issues, speak to your doctor about sleep aids to use temporarily.
  • Inform the examiner if you are very sleep deprived. They may reschedule you.


7. Medication Effects

A box of Xanax is laid out on a table.

Certain medications, supplements, and drugs can alter polygraph results by changing heart rate, blood pressure, and breathing depth. These include:



  • Inform the examiner of all medications you are taking, prescribed and over the counter. They will evaluate the risk.
  • Stop taking stimulants or depressants at least 24 hours prior if possible.
  • Avoid herbals like ephedra, ginseng, guarana, etc. close to test time.
  • Drink caffeine moderately the day of the test, not in excess.


8. Emotional Stress

Going through a very stressful life event right before or during the polygraph test can impact your mental state and alter results. Events like:

  • Divorce or breakup.
  • Family member death.
  • Losing job.
  • Financial hardship.


Even if the stressor is positive, the emotions and lack of stability can subconsciously manifest.


  • If an extremely stressful event just occurred, try to reschedule the test for a more stable time.
  • Incorporate relaxation techniques into your daily routine until the test date.
  • Avoid major life changes right before the test if possible.
  • Be upfront with the examiner regarding stress factors that may be impacting you.


9. Health Conditions

A woman looks anxious next to a window curtain.

Certain medical conditions can also affect your polygraph readings, including:

  • Heart disease.
  • Asthma or COPD.
  • Digestive disorders like IBS.
  • Neurological disorders like PTSD.
  • High blood pressure.
  • Respiratory infections.
  • Physical injuries causing pain.


The machine cannot differentiate between symptoms due to health problems versus deception.


  • Notify the examiner of medical conditions upfront, especially cardiac and respiratory.
  • Get health problems under control before the test through medication, diet, etc.
  • Reschedule if you have a cold, virus, or fit of IBS on test day.
  • Take prescribed medications normally before the test to keep symptoms stable.


10. Not Following Instructions

Some simple mistakes can doom your polygraph results. Things like:

  • Forgetting to stay still during the test.
  • Not listening carefully to all instructions.
  • Arriving very late and feeling rushed.
  • Taking medications against direction.
  • Having something stressful right beforehand like an argument.


The examiner will provide guidelines to follow before and during the test. But if you neglect to adhere to them, it will show in your readings.


  • Review instructions carefully at least 24 hours prior so they are fresh.
  • Allow plenty of time to arrive early and settle in.
  • Avoid altercations or stress right before the test.
  • Follow medical instructions exactly as directed.
  • Remind yourself to sit very still and focus.


While failing a polygraph test can be disastrous, with proper knowledge, you can set yourself up for success. Avoiding the most common mistakes that trip people up is half the battle. The rest comes down to staying calm, being honest, and listening closely to the examiner’s guidance.

With a good night’s sleep, a clear mindset, and trust in the process, you will be well on your way to passing. Stay positive but realistic. You’ve got this!


What questions will I be asked?
They pertain to the purpose of your test. Expect baseline questions first, then relevant questions about your possible deception.
No. Countermeasures do not work and will only backfire by raising suspicion and anxiety responses. Answer truthfully.
Certain conditions like COPD and heart disease can. Be upfront so the examiner is aware and can make accommodations.
Inform the examiner first. Slight movements won’t always affect results. Try to sit still during the critical question period.
No. Trying to rehearse “perfect” answers will backfire. Respond naturally and honestly in the moment.
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