How to Prepare for a Lie Detector Test: The Complete Polygraph Examination Guide

Preparing for a lie detector test is straightforward. Maintain your normal routine, get reasonable sleep, eat a normal meal, stay hydrated, take prescribed medication as directed and wear comfortable clothing. Avoid alcohol, recreational drugs and excessive caffeine. Arrive without rushing, communicate openly with the examiner, and make sure you fully understand every question before physiological recording begins.

In a professionally conducted polygraph examination, no relevant question should come as a surprise. All relevant questions are reviewed and agreed with you during the pre-test interview. The purpose of good preparation is not to learn how to “pass” a lie detector test or to manipulate the process. It is to create the conditions under which a fair, interpretable and professionally defensible examination can take place.

This guide, written by Dr Keith Ashcroft, investigative psychologist and principal forensic polygraph examiner at the Centre for Forensic Neuroscience, covers everything you need to know before, during and after a polygraph examination. Whether you have been asked to attend by a solicitor, therapist, employer, probation officer, safeguarding professional, or on your own initiative, the guidance here is the same.

What Preparing for a Polygraph Examination Really Means

Preparation for a polygraph examination is intended to support the conditions under which the procedure can be conducted fairly, safely and to a professional standard. It is not about learning techniques, rehearsing answers, or finding ways to influence the outcome.

Specifically, good preparation supports:

• Informed consent — understanding the process before agreeing to participate
• Clear question formulation — helping the examiner develop questions that are precise and unambiguous
• Physical comfort — arriving rested, fed and comfortable
• Concentration — being alert enough to listen carefully and respond accurately
• Communication — being able to express concerns, disclose relevant information and ask questions
• Suitability — ensuring the examination is appropriate given your current physical and psychological state
• High-quality physiological recordings — reducing avoidable artefacts or interference
• Responsible interpretation — providing the examiner with the context needed to interpret the data fairly

What the polygraph instrument records

A polygraph examination records several channels of physiological activity simultaneously during the question-and-answer phase. These typically include:

• Respiration — the rate, depth and pattern of breathing, recorded by pneumograph sensors around the chest and abdomen
• Electrodermal activity — changes in the electrical conductivity of the skin, recorded by sensors placed on the fingers
• Cardiovascular activity — relative changes in blood pressure and pulse rate, recorded by a cuff placed on the upper arm
• Movement or activity sensors — in some configurations, sensors that detect deliberate or involuntary movement during recording

It is important to understand that the polygraph instrument does not read thoughts. It does not independently determine whether someone is morally honest or dishonest. It records physiological data, which is then analysed and interpreted by a trained examiner using validated methods. The way a polygraph works involves comparing physiological responses to different categories of carefully structured questions.

What to Do During the Week Before the Examination

The period before a polygraph examination is an opportunity to organise your thoughts, communicate relevant information to the examiner and prepare practically. It is not a time for intensive research or anxiety-driven rehearsal.

Clarify the precise issue

Think about the specific matter the examination is intended to address. Identify the relevant events, the approximate date range, and the key factual questions. If you are instructing the examination yourself, prepare a concise chronology of the relevant events. If a solicitor, therapist or other professional has arranged the examination, they may have already communicated this information.

Provide relevant documents

If documents have been requested, send only those that are directly relevant to the examination issue. Avoid sending large volumes of unrelated material. If you are unsure what is relevant, ask.

Distinguish known facts from suspicions

If you are the person who has requested the examination, it is helpful to distinguish clearly between what you know to be factually established and what you suspect, believe or have been told by others. This distinction helps the examiner develop appropriate questions.

Explain uncertainty

If there are areas of genuine uncertainty — about dates, locations, the precise sequence of events, or the meaning of particular words — it is better to explain this honestly before the appointment than to discover the problem during the pre-test interview.

Inform the examiner about communication requirements

If you have a hearing impairment, processing difficulty, language need, or any other factor that may affect communication, inform the examiner in advance so that appropriate adjustments can be arranged.

Avoid obsessive online research

Reading general information about the polygraph process is reasonable. However, spending hours reading countermeasure advice, sensationalised accounts, or unreliable material is likely to increase anxiety rather than reduce it. Much of what appears online about polygraph examinations is inaccurate, outdated, or designed to generate attention rather than inform.

You do not need to formulate technically perfect polygraph questions yourself. Question construction is part of the examiner’s professional skill. Your task is to communicate the issue clearly and honestly.

How to Communicate with the Polygraph Examiner

Effective communication between the examinee and the examiner is one of the most important factors in a well-conducted polygraph examination. This section explains what to disclose, how to raise concerns, and why open communication protects you.

What to disclose before and during the pre-test interview

The following are examples of statements that examinees should feel comfortable making. They are not admissions of wrongdoing. They are responsible disclosures that help the examiner conduct a fair assessment.

• “I am unsure whether this question includes…”
• “I remember the event but not the exact date.”
• “This word has a different meaning to me.”
• “English is not my first language.”
• “I take the following prescribed medication.”
• “I have difficulty remaining still for extended periods.”
• “I feel under pressure to attend.”
• “I have remembered information that may affect the proposed questions.”

Honest disclosure of uncertainty is not the same as admitting deception. It is a sign of good faith and assists the examiner in ensuring that the questions are fair, the data is interpretable, and the examination is conducted to a professional standard.

Do not agree to a question simply to appear cooperative

One of the most important principles of a properly conducted polygraph examination is that the examinee must genuinely understand and agree to every question before physiological recording begins. You should not agree to a question when:

• The time period covered is unclear or too broad
• Important words have not been defined or could mean more than one thing
• The question combines multiple behaviours into a single yes-or-no format
• The question assumes a fact that you dispute
• The question asks about another person’s intentions or state of mind
• You cannot answer the question clearly with a yes or no
• You do not fully understand what is being asked

Agreeing to a question you do not understand does not make you appear cooperative. It introduces ambiguity, which compromises the quality of the physiological data and may produce an unreliable or uninterpretable result. A professional examiner will want you to raise concerns, not suppress them.

What to Eat Before a Lie Detector Test

No special diet is required before a polygraph examination. The best approach is to eat normally.

• Eat a normal meal at your usual time before the appointment. Arriving hungry can affect your comfort, concentration and general wellbeing during the examination.
• Do not deliberately fast. Fasting can cause light-headedness, irritability and difficulty concentrating, none of which are helpful.
• Avoid an unusually large meal immediately before the appointment. Excessive fullness can cause discomfort when sitting for an extended period.
• Choose a familiar meal. The appointment is not the time to try unfamiliar foods or supplements.
• Bring a snack if medically required. If you have diabetes or another condition that requires you to eat at specific intervals, bring appropriate food or glucose treatment.
• Avoid unfamiliar supplements or “detox” products. These are unnecessary and may cause unpredictable effects.

Examples of suitable ordinary meals include toast or cereal, a sandwich, soup, a pasta dish, or whatever you would normally eat at that time of day. None of these is medically recommended for a polygraph examination — they are simply examples of normal meals.

Hydration, Caffeine and Energy Drinks

Drink water normally throughout the day. Do not deliberately dehydrate yourself before the appointment, and do not overhydrate in an attempt to influence the outcome. Normal hydration supports comfort and stable physiological recordings.

A normal amount of tea or coffee is generally preferable to a sudden and complete change in your usual caffeine intake. If you normally drink two cups of coffee in the morning, your usual routine is unlikely to cause a problem. However, consuming significantly more caffeine than you normally would — or consuming high-caffeine energy drinks — may increase restlessness, muscle tension and cardiovascular activity, which can affect the quality of physiological data.

Equally, sudden caffeine withdrawal in habitual users may cause headaches, fatigue, irritability and difficulty concentrating. The general principle is to maintain your normal routine rather than making significant changes immediately before the appointment.

Caffeine does not automatically invalidate a polygraph examination. The concern is with excessive or unusual consumption, not with normal dietary habits.

Medication and Health Conditions

Continue to take all prescribed medication as directed. Medication use does not automatically make someone unsuitable for a polygraph examination. Suitability must be assessed individually, and the examiner needs accurate information to make that assessment. For more detail on how suitability is assessed, see the pre-screening questionnaire.

What information to disclose

When you attend, inform the examiner about:

• The name of each medication you are taking
• The dose
• The time you last took it
• How long you have been taking it
• Any recent changes to your prescription
• Any significant side effects you are experiencing

Over-the-counter products

In addition to prescribed medication, also mention:

• Cold remedies and decongestants
• Antihistamines
• Pain medication (including codeine-containing products)
• Sleep aids
• Pre-workout or stimulant supplements
• Herbal or “natural” products taken regularly

The examiner is not making a medical judgement about your medication. The information is needed to assess whether the examination can proceed appropriately and to take relevant factors into account during interpretation. If you have specific concerns about how medication may interact with the polygraph examination, raise them with the examiner.

Alcohol and Recreational Drugs

Do not attend a polygraph examination while intoxicated or significantly impaired by alcohol or recreational drugs. Substance use can affect your ability to participate meaningfully, to concentrate, to give informed consent, and to produce physiological data that can be reliably interpreted.

Avoid alcohol for at least 24 hours before the examination. Avoid recreational drugs entirely.

If you have used alcohol or drugs before the appointment, disclose this to the examiner. Concealment is unhelpful. If impairment is evident, the examiner may decide to postpone the examination. Postponement in these circumstances is a professionally appropriate decision, not a punishment.

If you are physically dependent on alcohol or another substance and abrupt cessation would be medically unsafe, do not attempt unsupervised withdrawal. Discuss the situation with the examiner in advance so that appropriate arrangements can be considered.

Sleep and Fatigue

Aim for a normal night’s sleep before the appointment. This does not need to be perfect sleep — some difficulty sleeping before an unfamiliar event is entirely normal and not a reason to panic.

• Do not stay awake the night before researching countermeasures or obsessively reading about polygraph examinations.
• Do not self-medicate with sleeping pills, alcohol, or sedative products you would not normally take.
• If you experience severe fatigue — for example, from shift work, illness, or prolonged insomnia — disclose this to the examiner.
• Severe fatigue may require the examination to be postponed if it would significantly affect your ability to concentrate and participate.

Mild tiredness is manageable and expected. Severe sleep deprivation is a different matter and should be raised honestly.

What to Wear to a Polygraph Test

Clothing should be comfortable and practical. You will be sitting for an extended period, and sensors will be placed on your upper body, fingers and upper arm.

Recommended

• Comfortable, loose-fitting clothing
• Clothing that permits access to the upper arm (for example, short sleeves or sleeves that can be rolled above the bicep)
• Removable layers, as room temperature may vary
• Clothing suitable for sitting in one position for up to two hours
• Clean, dry hands

Avoid

• Highly restrictive garments that may affect breathing patterns or comfort
• Bulky outerwear worn throughout the examination
• Excessive layers around the chest or abdomen, which may interfere with respiratory sensors
• Jewellery, watches or accessories that cause repeated fidgeting or movement
• Applying large amounts of hand cream immediately before the appointment, as this may affect the electrodermal sensors

What to Bring

• Photographic identification, if requested
• Appointment confirmation or address details
• Glasses or contact lenses if you need them to read
• Hearing aids
• A written list of current medication
• Essential prescribed medication (including inhalers)
• Diabetes monitoring equipment or glucose treatment where relevant
• Any case documents previously agreed with the examiner or instructing professional
• Contact details for the instructing solicitor, therapist or other professional, if applicable

A supporter — such as a partner, friend, parent or advocate — may accompany you to the location. However, supporters are not normally present in the examination room during the procedure. Exceptions may be made where a support person is required for communication, accessibility or safeguarding reasons. This should be discussed with the examiner in advance.

Arriving at the Appointment

• Plan the journey. Check the location, parking, public transport and any access requirements in advance.
• Allow for delays. Arriving late can increase stress and may reduce the time available for the pre-test interview.
• Avoid arriving in a rush. A few minutes to settle is helpful.
• Use the toilet before physiological recording. Once the sensors are attached, the recording phase should proceed without unnecessary interruption.
• Silence your telephone. Interruptions during recording can affect data quality.
• Avoid scheduling an urgent appointment immediately afterwards. Feeling pressed for time may affect your comfort and concentration.
• Allow approximately two hours unless otherwise advised by the examiner.

What Happens During a Polygraph Examination

A professionally conducted polygraph examination follows a structured sequence. Understanding the stages may help reduce uncertainty about the process. For a more detailed explanation, see how a polygraph examination works.

1. Introduction and identification — the examiner confirms your identity and explains the purpose of the appointment
2. Explanation of the procedure — the process, the equipment and your rights are explained in plain language
3. Suitability assessment — the examiner reviews your current health, medication, emotional state and readiness to proceed
4. Informed consent — you confirm that you understand the procedure and agree to participate voluntarily
5. Pre-test interview — a detailed discussion of the relevant issue, the background and the specific questions
6. Question formulation and review — the questions are finalised and you confirm that you understand every one
7. Acquaintance or practice procedure — where applicable, a brief familiarisation with the question-and-answer format
8. Placement of sensors — the pneumograph tubes, electrodermal sensors and blood pressure cuff are attached
9. Physiological recording — several short recording sessions (charts) are conducted
10. Data analysis — the recorded physiological data is scored using validated methods
11. Post-examination discussion — the examinee has the opportunity to comment on the data and provide further information
12. Verbal feedback and written reporting — where commissioned, the examiner provides a verbal summary and a formal written report

The pre-test interview is a substantive part of the examination. It is not merely an administrative step and should not be rushed. A thorough pre-test interview supports clear question formulation, accurate informed consent and high-quality physiological data.

How to Answer During Physiological Recording

During the recording phase, the examiner will ask the agreed questions one at a time. Your task is straightforward:

• Listen to the entire question before responding. Do not anticipate or begin your answer before the question is complete.
• Answer only after the question has been completed. A brief pause is normal and expected.
• Give the agreed yes-or-no response. Do not change your answer, add qualifications, or offer explanations during the recording.
• Speak normally. There is no need to whisper, shout, or alter the way you naturally speak.
• Remain reasonably still. Avoid deliberate movement, fidgeting, shifting position, or adjusting clothing during each chart.
• Avoid adding explanations during the chart. If you have something to say, the opportunity will come between charts.
• Raise concerns between charts. If something is troubling you — a question, a sensation, discomfort — mention it between recording sessions.

Qualification and clarification should occur before recording, not during the answer. If you realise during a chart that you are unsure about a question, complete the current chart and raise the issue with the examiner before the next one.

Managing Lie Detector Test Anxiety

Feeling nervous before a polygraph examination is entirely normal. Most people experience some degree of anxiety about the process, the equipment, or the significance of the outcome. This is understood, expected and accounted for in the design of the examination.

A professionally conducted polygraph examination does not simply measure whether someone feels anxious. The procedure is comparative in nature — it examines differences in physiological responses between different categories of questions, not the absolute level of arousal.

Common concerns

• Fear of not being believed. Many people worry that even if they are truthful, the examination will somehow produce the wrong result.
• Fear that nervousness will be mistaken for deception. General nervousness about the situation is a baseline condition, not evidence of deception.
• Anxiety about unfamiliar equipment. The sensors are non-invasive and painless. The examiner will explain each one before it is attached.
• Concern about the importance of the outcome. The stakes may feel high. Acknowledging this to the examiner is appropriate and helpful.
• Worry caused by online material. Inaccurate or sensationalised information about polygraph examinations can significantly increase anxiety.

Practical steps

• Ask questions about anything you do not understand
• Explain to the examiner how you are feeling
• Arrive early enough to settle
• Eat normally beforehand
• Mention any physical discomfort during the process
• Request reasonable adjustments if you need them
• Focus on understanding and answering each agreed question, one at a time

It would not be responsible to promise that anxiety can never affect physiological data under any circumstances. However, general nervousness about the examination itself is a normal and expected condition, and a trained examiner will take it into account when interpreting the results.

Polygraph Preparation Dos and Don’ts

Countermeasures and Online Misinformation

Countermeasures are deliberate actions taken by an examinee with the intention of influencing or manipulating physiological recordings during a polygraph examination. Examples that appear in published literature include manipulated breathing patterns, deliberate muscle tension, pain, deliberate movement, mental calculations, and timed cognitive tasks.

It is important to understand that attempting countermeasures may:

• Introduce artefacts into the physiological recordings
• Reduce overall data quality
• Produce an inconclusive or no-opinion outcome
• Cause the examination to be stopped
• Be documented in the examiner’s report
• Undermine confidence in the examinee’s cooperation and the credibility of the examination

Much of the material available online about “beating” a lie detector test is unreliable, oversimplified or directly misleading. A trained examiner is aware of common countermeasure strategies, and modern computerised physiological monitoring equipment includes features designed to detect certain types of deliberate interference.

The purpose of this guide is to help you prepare for a fair, well-conducted examination — not to teach or encourage countermeasures. The most effective preparation is honest participation.

When to Contact the Examiner or Postpone

Postponement is not a failure. In many of the circumstances listed above, postponement is the professionally defensible decision. Proceeding when an examinee is acutely unwell, significantly impaired or unable to give informed consent may produce unreliable data and raises ethical concerns.

Pregnancy

Pregnancy requires an individual assessment. It is neither automatically suitable nor automatically unsuitable for a polygraph examination. The decision depends on the specific circumstances.

If you are pregnant, please disclose:

• The stage of your pregnancy
• Whether it is uncomplicated or high risk
• Any current symptoms that may affect your comfort
• Any relevant medical advice you have received
• Whether prolonged sitting is comfortable for you

The examiner will consider these factors and may consult with relevant professionals before deciding whether to proceed. In some cases, postponement may be more appropriate. In others, the examination may proceed with appropriate adjustments to ensure comfort and safety.

Neurodiversity, Trauma and Communication Adjustments

The Centre for Forensic Neuroscience recognises that examinees have diverse communication needs, cognitive profiles and psychological histories. A polygraph examination should be accessible to the individual being assessed, without compromising its evidential purpose. For our detailed approach, see the article on neurodiversity and polygraph examinations.

Conditions and circumstances that may require adjustments include:

• Autism spectrum conditions
• Attention deficit hyperactivity disorder (ADHD)
• Dyslexia and other specific learning differences
• Post-traumatic stress disorder (PTSD)
• Anxiety disorders
• Hearing impairment
• Language needs (including examinees for whom English is not their first language)
• Processing difficulties
• Sensory sensitivities

Possible adjustments

• Plain language throughout the pre-test interview and questions
• Literal wording that avoids idiom, ambiguity or abstraction
• Additional processing time between questions
• Reduced environmental distractions
• Clear explanation of each stage before it occurs
• Breaks during the examination
• Written confirmation of agreed questions
• An interpreter where appropriate
• Sensory adjustments (lighting, sound) where practical

The aim is to make the examination accessible and fair. If you have a condition or need that may affect your participation, please inform the examiner as early as possible so that appropriate adjustments can be considered.

What Happens After the Recording

The post-examination phase is an important and sometimes overlooked part of the polygraph process. After the physiological recording is complete, you should have a reasonable opportunity to comment on the data, explain any reactions you were aware of, and provide any further information that may be relevant. For a full discussion, see our article on what happens after a lie detector test.

Before leaving the appointment, you should understand:

• The terminology used for the result (for example, what “no significant reactions”, “significant reactions” or “inconclusive” means in practice)
• Whether the verbal outcome provided is provisional pending quality assurance
• Whether a quality assurance review is required
• Whether a written report was commissioned and who receives it
• What an inconclusive or no-opinion result means
• Whether any further information, documents or follow-up is required

A polygraph result should be considered alongside other available evidence and information. It is not a medical diagnosis, a legal verdict or a guarantee of truthfulness. Where a polygraph examination has been arranged by a solicitor, therapist or other professional, the result should be discussed with that professional in the context of the wider matter.

Frequently Asked Questions

This article is provided for general information only. A polygraph examination is not a guarantee of truthfulness, a diagnosis, or a legal verdict. Results should be interpreted cautiously and in context. Where there are legal, medical, or safeguarding concerns, appropriate professional advice should be sought independently.

Dr Keith Ashcroft is an investigative psychologist, polygraph examiner, and member of the American Polygraph Association at the Centre for Forensic Neuroscience. To discuss whether a polygraph examination may be appropriate for your circumstances, or to understand the cost of a lie detector test, contact Dr Ashcroft for a confidential consultation.