Driving Under The Influence of Drugs
Drug-Induced Driving Impairment

Drug-Induced Impairment of Driving Skills: Vision, Perception and Judgment

Updated Dec. 25, 2020

All drugs can have an adverse effect on your physical and mental driving skills. As a novice driver, you must be aware that you can be stopped and arrested for DUI (driving under the influence) or DWI (driving while intoxicated) if you are impaired by any drug. This is true for prescription and over-the-counter medications as well as recreational substances.

This module explores precisely how different types of drugs can impair your driving ability. Depressants, stimulants and hallucinogens all have different biological actions which can result in different impairments. If you know what to look out for, you can monitor your physical and mental well-being and avoid getting into the driver’s seat while intoxicated. Let’s begin by looking at two of the most important physical attributes you need to drive safely: good vision and physical coordination.

Drug-impaired vision

Good vision is essential to drivers. If you cannot accurately perceive the situation on the roadway around and ahead of your vehicle, you cannot make safe driving decisions or act to avoid danger. Drugs will impair your vision to some degree and even very minor impairments will leave you more in danger of overlooking important information and having an accident.

Depressants such as alcohol, heroin, benzodiazepines and prescription opioids will slow down the central nervous system and impair the movement of the tiny muscles which control eye movement. This will prevent you from scanning the roadway effectively and can lead to object fixation.

Stimulants such as nicotine, Ritalin, caffeine and cocaine can overstimulate eye muscles, leading to excessive eye movement. This will make it harder for you to focus on a single point and collect detailed visual information about a specific area of the road ahead.

Hallucinogens such as LSD and marijuana can also hinder natural eye movement, causing drivers to collect insufficient visual information. In addition, the driver may experience hallucinations and see things on the roadway which are not actually there!

Drug-impaired coordination

Drugs that affect the central nervous system can disrupt signals sent from the brain to control muscles. As a result, they can impair your movement, balance and coordination – three physical skills that are vital to drivers.

Depressants can lead to numbness, slowed movement, heavy limbs and loss of balance.

Stimulants can cause tremors, shaking, compulsive movements and the inability to keep still.

Hallucinogens could have either of these effects. Your movements may be restless and compulsive or slow and off-balance. The sense of detachment from one’s surroundings that people often experience when using a hallucinogen can also lead to inaccurate movements. This could leave you unable to find a pedal with your foot or locate vital hand controls.

Whatever the precise physical effects of the drug that has been taken, the driver will be rendered less capable of controlling their vehicle and consequently more likely to be involved in a collision.

Impairments caused by stimulants

Any substance with a stimulant effect will intensify brain activity and “turn up” signals sent from the central nervous system to the rest of the body. Stimulants often create feelings of anxiety and aggression. Your brain will be overactive and unable to focus on individual tasks effectively. While driving, everything around you will appear to be moving at a frustratingly slow pace in comparison to your racing mind. You will also be extremely susceptible to distraction and as a result, likely to make mistakes that will anger other road users. This is a recipe for conflict, aggressive driving and road rage.

Drivers who are under the influence of stimulants are easy to spot. Some common tell-tale signs are:

  • Tailgating
  • Driving at excessive speeds
  • Frequently changing lane position
  • Frequent passing and lane changing
  • Ignoring right-of-way rules
  • Ignoring traffic control devices
  • Generally risky behavior
  • Failure to communicate with other road users
  • Jerky braking and acceleration

Here is a break-down of the ways in which stimulant drugs will affect your key driving skills:

  1. 1

    Your gaze may shift too much, making it difficult to collect detailed information about the road. You may also stare blankly at what you see, without fully taking in the information.

  2. 2

    Stimulants make it incredibly difficult to pin your mind down to a single task. You may become distracted by past and future events that have nothing to do with your immediate surroundings or the task at hand.

  3. 3

    Everything will appear to be happening slower than it actually is. You will likely misjudge the speed and distance of other objects and drive faster than you intend to.

  4. 4

    Stimulants will make it harder for you to access stored memories without being distracted by other events and ideas. You may also have difficulty associating memories with what you see around you and deciding which information deserves your attention. Your mind will be moving faster but you will take longer to process information and make decisions.

  5. 5

    It is unlikely you will be able to think things through well enough to make safe decisions. Your ability to think ahead will also be hindered. For instance, you may make the snap decision to rush through an intersection before the light changes, without stopping to consider that you may collide with other traffic as you reach the other side.

  6. 6

    Stimulants can create a feeling of invulnerability, leaving drivers considerably more inclined to ignore risk and make dangerous judgments.

Impairment caused by depressants

Depressants disrupt the central nervous system by suppressing brain function and “muffling” the signals sent from the brain to control the rest of the body. All your vital bodily processes (including digestion, circulation and respiration) will be slowed. Depending on the strength of the drug, you may feel extremely calm, sleepy and detached from the world around you.

While under the influence of a depressant, everything your body and brain do takes longer and is more difficult. You will find it harder to complete simple physical tasks and will take considerably longer than usual to consider information and make decisions. Together, these effects add up to an extremely extended reaction time which could be fatal if you’re driving.

A driver who is intoxicated with a depressant drug will not comprehend danger in the same way as a sober driver. In fact, they may not comprehend danger at all. Their sense of detachment from their surroundings may be so profound that they do not understand why they must try to avoid collisions.

The physical and mental impairments caused by depressant drugs are generally very similar to those caused by alcohol. However, some depressant drugs have different effects, for instance:

  • Benzodiazepines such as Xanax and Valium often create a heightened feeling of detachment and are more likely to lead to aggression.
  • Barbiturates such as Seconal and Nembutal generally impair muscle coordination more so than alcohol.
  • Pain relievers can impair the pupil’s response to light changes sooner and more significantly than alcohol.
  • Antihistamines tend to cause lightheadedness and cognitive confusion before loss of muscle control.

Here’s how most depressant drugs will impair your vital driving skills:

  1. 1

    Your eye muscles will not respond to signals from the brain as efficiently as usual, making it harder to move your gaze around the roadway quickly. Pupil dilation and contraction will also be slowed. As a result, it will take longer for your vision to adjust as you drive through poorly lit areas, and you may be temporarily blinded by sudden increases in light.

  2. 2

    Depressants create a sense of detachment and can lead people to become lost in thought. It will be practically impossible to pay attention to the driving task while under the influence of a depressant.

  3. 3

    You will find it difficult to judge distances and other objects may appear to move faster than they truly are. It is quite common for depressant-intoxicated drivers to travel at dangerously slow speeds. That is, until they fall asleep at the wheel with their foot resting on the accelerator.

  4. 4

    Depressants are known to impair both short-term and long-term memory. You will not remember something you have just seen long enough to decide what to do about it and even if you could, you will not recall the necessary information from your driver’s training to act appropriately.

  5. 5

    Your cognitive processes will be significantly slowed when a depressant drug is in your system. By the time you have perceived a hazard and decided what to do about it, you probably will have collided with it already.

  6. 6

    Depressant drugs can create feelings of extreme apathy. You may be incapable of caring about your own well-being or the lives of other road users. As a result, you will not be equipped to make risk-reducing decisions.

Impairment caused by hallucinogens

Hallucinogenic drugs are extremely unpredictable and can severely impair a driver’s perception and judgment. They can impair memory, distort cognition, cause delusions and hallucinations! Having a negative experience with hallucinogenic substances can be very frightening and cause permanent psychological damage. Having a distressing hallucination will cause intense fear, anxiety and panic, which would lead to extremely dangerous behavior behind the wheel. Even having a positive experience with hallucinogenic drugs would be a disaster if you intend to drive, as you may see, hear, feel and react to things within your car and on the roadway around your vehicle which are not really there.

The chances of overdosing with a hallucinogen are less than with depressant or stimulant drugs, though this does not make them any less dangerous. People under the influence of hallucinogens can get so caught up in the delusion or hallucination they are experiencing, that they jump off buildings, deliberately mutilate themselves or drive straight off the side of the road – on purpose!

People do not always experience vivid, visual hallucinations when taking a hallucinogenic drug. Some hallucinogens are better known for distorting the user’s perception of reality. If this happens, you may end up believing things about yourself, your life and the outside world which are upsetting and untrue. This type of paranoid delusion can result in aggressive, unpredictable driving behavior. You may even set out to harm other road users with your vehicle and believe yourself to be completely justified in doing so.

A driver under the influence of hallucinogens may exhibit the following behaviors:

  • Driving at excessively high or low speeds
  • Speeding up and slowing down erratically
  • Slowing down or stopping in inappropriate places, such as on expressways
  • Attempting to complete impossible maneuvers and other risk-taking behavior
  • Utter disregard for changes in roadway conditions
  • Driving in a manner that appears to be fueled by fear, panic or anxiety

Here’s how hallucinogenic drugs will impair your driving skills:

  1. 1

    The movement of your eye muscles may either speed-up or slow down, making it difficult to follow proper roadway scanning procedures. Hallucinations caused by the drug will make the visual information you collect inaccurate. Your hallucination may be all-consuming and completely block out reality. Alternatively, you may see objects in the real driving environment that are not there and be unable to tell which of what you are seeing is real, and which is not.

  2. 2

    Any hallucinogen will impair your focus. A drug that actually produces hallucinations will distract you from the driving task with images, sounds and sensations which are not there. A dissociative hallucinogen will totally disengage you from the act of driving with a feeling of being detached from your body and sense of self.

  3. 3

    Hallucinogens often distort the user’s perception of time and space. You will be completely unable to judge distances, maintain space around your vehicle, estimate the speed of other road users or appropriately manage your own speed.

  4. 4

    Hallucinogenic substances can cause serious memory impairments. Certain key memories and fragments of information necessary to your driving performance may be lost altogether. Your mind may also invent memories of events that never occurred or misconstrue real memories.

  5. 5

    Your ability to reason depends on collecting accurate visual information and accessing the memories necessary to understand it – neither of which you will be able to do while under the influence of a hallucinogen. It is likely that you will make driving decisions that are wildly inappropriate for the conditions on the road.

  6. 6

    Feelings of wonder, joy, anxiety, fear or anger may completely shift your priorities and leave you more susceptible to putting yourself and other road users at risk. You may understand that making a U-turn in the middle of a busy highway is a bad idea but consider it a necessary evil to avoid some hallucinated danger.

Come down and rebound impairments

After the initial effects of any stimulant, depressant or hallucinogen have worn off, there will be a period during which your body tries to re-balance itself and return to a “normal” state. With many regular prescription medications, this is less of an issue, as your doses will be arranged to keep you “topped-up” and experiencing the therapeutic benefits of the drug throughout the day. With recreational drugs, people often experience a come down as the drug wears off, followed by a rebound as the body seeks to counteract the effects of the drug. If you are coming down or rebounding, your driving skills will still be impaired.

Come downs vary based on the drug in question and the amount that was taken, but they are often very unpleasant for the user. Drugs that produce a euphoric effect usually result in the worst comedowns; as the drug leaves your system, feelings of elation and happiness will be replaced by sadness, anxiety, paranoia and even anger. This will likely result in distracted or aggressive driving behavior. Plus, your reaction time will still be noticeably extended by the residual effects of the drug in your bloodstream. Do not drive if you are experiencing a come down from any substance – this includes hangovers!

When the effects of whichever drug you have taken have completely worn off, your body will enter a rebound phase. This can last anything from a few hours to several days, depending on the drug, the dose and a variety of other factors. While you are rebounding, your central nervous system will attempt to right itself by actively counteracting the primary action of the drug. Therefore:

  1. Rebounding from a stimulant will produce depressive symptoms. The user may feel sleepy, lethargic, depressed and suffer from slower movements and cognition.
  2. Rebounding from a depressant will produce stimulant-like symptoms. The user may feel agitated, anxious, restless and suffer from racing thoughts.
  3. Rebounding from a hallucinogen can produce a variety of effects, as these drugs may have depressant or stimulant-like qualities. Users can also experience “flash-backs” of hallucinations and experiences they had while under the influence, for quite some time after the drug has worn off.

As you can see, rebounding from any drug can result in significant impairments to your driving skills. Powerfully unpleasant rebounds can also lead to repeat drug use and long-term abuse, as the user takes more of the drug to ease the symptoms of the after-effects.

Drug use and driving don’t mix

Many people think they can use recreational drugs and still be good drivers, simply by not driving until they are sober, but it doesn’t work that way. If you are a regular or semi-regular recreational drug user, you can never really be a safe and capable driver. Your body will practically always be impaired in some way, due to the initial intoxicating effects of the drug, followed by the comedown and the rebound phase.

Prescription drug users must learn to cope with the side-effects of their medication and know when to stay off the road, as they have no choice. Recreational drug users do have a choice. Unless you have been prescribed medication to treat a health problem, there is absolutely no need to mess around with drugs, damage your body and become an unsafe driver.

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