Driving Under The Influence of Drugs
Driving Under The Influence of Drugs

Driving Under The Influence of Drugs: Impaired Driving, Laws & Penalties

Updated Dec. 25, 2020

For most people, the word “drug” tends to invoke the idea of illegal substances, like heroin, cocaine or marijuana. Drugs are, in fact, a far broader category of substances. As a society, our relationship with drugs varies dramatically depending on the legality of the substance and whether it has any accepted medical uses. Most of us would recoil in horror if somebody offered us heroin or methamphetamine but wouldn’t think twice about popping a couple of aspirin to alleviate a headache.

The technical definition of the word drug is:

“A medicine or other substance which has a physiological effect when ingested or otherwise introduced into the body.”

By this definition, alcohol is a drug. So too are prescription medications, aspirin, cold remedies, caffeine and even cough syrup!

Granted, most illegal drugs have the potential to be far more harmful than over-the-counter pain medication. However, all drugs create a chemical reaction when taken into the body that temporarily alters the way your body works. For that reason, all drugs can be dangerous and have the potential to impair your driving ability.

Many drugs have therapeutic benefits that can improve the quality of life for a person suffering from pain, illness or chronic disease. These medicinal drugs need not be avoided if your doctor or another medical professional believes you should take them. However, they must still be treated with caution and respect, as taking too much of any drug can be deadly. Never take any prescription medication that was not specifically prescribed to you and when taking medication, you must always stick to the stated dose on the packet. All drugs have three, unique dose thresholds:

  1. 1

    A minimum dosage.
    The point at which the drug takes effect on the body. Any dose below this threshold would be ineffective.

  2. 2

    An effective dosage.
    The point at which the drug provides the maximum therapeutic benefit.

  3. 3

    A lethal dosage.
    Doses at or above this amount will be fatal.

People who use drugs frequently (whether for medicinal or recreational purposes) will gradually build up a tolerance to the substance. This means the amount of the drug they must take to achieve an “effective dosage” increases over time. The gap between an effective dose and a lethal dose will gradually narrow, increasing the risk of an accidental overdose occurring.

You probably already realize that it is possible to overdose on substances like cocaine, heroin, methamphetamine, prescription medications and even over-the-counter medications. However, these are not the only drugs you need to be wary of. Many perfectly legal substances can be lethal if taken in a large enough dose, even two of the most frequently consumed drugs: caffeine and nicotine.

  • A lethal dose of caffeine is around 10g. The average cup of coffee contains between 100 and 200mg. A person would have to drink 50 to 100 cups of coffee in a very short space of time to achieve a lethal dose. However, many diet pills and similar medications contain a far greater dose of caffeine and have a much greater potential for overdose, as it is easier to swallow 10 pills than it is to drink 50 cups of coffee.
  • A lethal dose of nicotine is around 40 to 60mg. A person would have to smoke roughly two whole packs of cigarettes in immediate succession to achieve this dose. However, doses far lower than this are still toxic and have been shown to produce a whole host of dangerous physiological effects – more bad news for chain smokers!

Using any drug improperly or irresponsibly can cause unpleasant short-term side-effects, long-lasting physical and mental illness, permanent damage to your brain and body, or death. As a new driver and a young adult, you must understand the consequences of putting chemical substances in your body.

Some drugs are totally illegal, others are legal to buy with a prescription and many are legal to purchase over the counter in just about any store around the country. Drugs are also “hidden” in many popular consumer products that claim to help you lose weight, stay alert, study harder, have clearer skin or sleep better. If a product suggests it can alter the normal functioning of your body in some way, treat it with extreme caution. Remember that legal does not always equal safe!

Legal drug use

Legal medications and drugs can be used responsibly. While this does not make them 100% safe, it does dramatically decrease the risk of injury, illness, impairment and overdose. For instance:

  • Morphine and similar opiate pain killers can be used safely under the supervision of a medical professional. This type of drug may be prescribed if you were to visit an emergency room with a fractured arm or similarly painful injury.
  • Sedatives may be prescribed by a pharmacist to somebody suffering from disordered sleep.
  • Aspiring or ibuprofen can be bought and taken by any person wishing to relieve the symptoms of flu or a cold.

Of course, the key to these situations qualifying as “responsible” drug use is that the medications would be taken:

  • With prescription and supervision from a medical professional and/or
  • With exact adherence to the medical guidelines on the packaging

Each of the drugs mentioned in these examples has the potential to be very dangerous if taken too frequently or in too large a dose. Doctors and pharmacists undergo years of medical training to be qualified to decide whether and under what circumstances a drug is safe to use, based on a patient’s age, health, medical condition and any existing medications they are taking. Drugs that can be purchased without permission from a doctor still come with strict dose and frequency guidelines printed on the leaflet inside the packet. The only difference is that these drugs are considered slightly less dangerous, so people are allowed to read the guidelines and administer the drugs themselves.

Drug-impaired driving

Drug-impaired driving is a growing problem in the United States. Due to the wide variety of different legal and illegal substances that can impair a person’s driving ability, it is a problem that federal and state law enforcement agencies find challenging to tackle. Marijuana is the drug most often found in the toxicology reports of impaired drivers, traffic crash victims and those involved in fatal collisions. Prescription medications such as opioid painkillers, amphetamines (such as Ritalin) and benzodiazepines also feature prominently in the list of substances found in impaired drivers.

Unlike alcohol, drugs vary so dramatically in their effects that setting a comprehensive legal limit at which people cannot drive while under the influence of a drug is practically impossible. Plus, many intoxicating substances cannot be detected with a breathalyzer test if a police officer were to pull somebody over on suspicion of DWI. Thus, where legal substances are concerned, the responsibility of determining whether one is “fit to drive” falls to the drivers themselves. Sadly, many drivers do not even realize that a medication they are taking has the potential to impair their driving ability.

Relatively low doses of many prescription and over-the-counter medications can render a person unfit to drive. Whenever you are prescribed a new medication or a higher dose of an existing medication, be sure to discuss the potential impact on your driving ability with your doctor. You must also monitor your physical and mental well-being yourself, as some people are sensitive to certain drugs and can become impaired at far lower doses.

Who is at risk?

If a person drives while impaired by drugs, every other road user they encounter on their journey will be at risk of sustaining a serious injury or being killed. According to the National Survey on Drug Use and Health which was conducted in 2014, teenagers and young people are the most at risk of getting behind the wheel while impaired by drugs.

NSDUH Statistics

10.2 million people aged 12 and over admitted to driving while under the influence of drugs, at least once in the year prior to the survey.


Young adults aged between 18 and 25 were determined the most likely to drive under the influence of drugs.


10% of 18 to 25-year olds admitted driving under the influence of drugs at least once in the year prior to the survey.

In addition to being the most likely to commit a drug-impaired driving offense, teenagers and young adults are the most likely to die or be seriously injured in a drug-fueled accident. Teenagers are natural risk-takers due to their limited life experience. Plus, they do not have the benefit of many years of driving experience to help them identify risks and make safe decisions behind the wheel. Worsening these existing handicaps with drug impairment is a recipe for tragedy and disaster.

Scheduled drugs

So, who decides how and under what circumstances a drug can legally be used? That responsibility falls to the drug enforcement administration (DEA) and the food and drug administration (FDA). Based on whether a drug has medical applications, its potential to cause harm, how likely it is to be abused and its international status, these two federal agencies assign the substance a rank in the controlled substances act – which is the topic of discussion in our next article.

If a drug is “controlled” there are legal restrictions on how it can be used. The controlled substance act is split into five “schedules”. Schedule I contains the most dangerous drugs. As we move through schedules II to V, the drugs become gradually less dangerous and heavily regulated. Depending on which schedule a drug falls in to, it may be:

  • Illegal for all uses bar scientific research.
  • Legal for medical use with a prescription but automatic refills are not allowed.
  • Legal for medical use with a prescription but can only be refilled five times and for no more than six months after the original prescription.
  • Legal for medical use without a prescription.

The controlled substances act covers most medical and recreational drugs. However, substances that are unscheduled (not covered in the act) can still be incredibly harmful. Alcohol and tobacco are probably the two best examples of this, as they kill hundreds of thousands of people every year and have no medical applications yet are legal for any adult in the country to buy and use recreationally.

Drug types and their effects

Part three of this section discusses different types of drugs and their likely effects on your body and mind. There are thousands of different drugs currently being used for experimental, medical and recreational purposes, some of which are naturally occurring (taken from plants) while others are synthetic (made in a laboratory). The vast majority of these substances fall into one of three categories, based on the effect they have on the central nervous system:

  • Stimulant drugs – speed up the body’s natural processes.
  • Depressant drugs – slow down the body’s natural processes.
  • Hallucinogenic drugs – may either speed up or slow down the body’s natural processes and can cause hallucinations.

The precise effects of a stimulant, depressant or hallucinogen vary based on the individual drug and a whole host of other factors, including:

  • The user's mental and physical health
  • The user's state of mind
  • The dose of the drug
  • Other substances in the user’s bloodstream when the drug is taken

All drugs have the potential to cause short-term distress, long-term health problems, mental health issues and driving impairment. Drugs that can cause physical addiction or psychological dependency are particularly dangerous, as users may continue to take them despite negative side effects and health implications. The next three modules will introduce you to the most common stimulant, depressant and hallucinogenic drugs and the likely effect they will have on your body. Here’s a quick preview:


Stimulants such as nicotine, cocaine and methamphetamine intensify the signals sent from your brain to the rest of your body, resulting in heightened body temperature, faster breathing, rapid heart rate and initially, a false sense of well-being. They can also just as easily cause anxiety, anger, shaking, loss of physical coordination and erratic behavior, all of which would seriously impede your ability to control a vehicle, detect changes in the roadway environment and make safe driving decisions. A driver under the influence of a stimulant drug is more likely to overreact to minor adverse events, behave aggressively toward other road users, exceed a safe speed and take unnecessary risks.


Depressants such as heroin, medicinal opiates (e.g. morphine, hydrocodone, methadone), benzodiazepines and barbiturates muffle the signals sent from your brain to the rest of your body. This will result in slowed respiration, slower metabolism, slowed heartbeat and a drop in body temperature. Contrary to what the name might suggest, depressants often create a sense of calm and general well-being. For this reason, medicinal depressants are commonly prescribed to treat pain, mood disorders, anxiety and sleep problems.

Depressants can also cause drowsiness, unconsciousness, extreme apathy (not caring about things that usually matter to you), loss of physical coordination and slowed reactions. If you were to drive under the influence of a depressant drug, your reaction time would be dangerously extended, you would have difficulty processing events on the roadway and may even fall asleep at the wheel!


Hallucinogens such as LSD, PCP, Ketamine, marijuana and dextromethorphan (the active ingredient in cough syrup) confuse chemical messages sent in the brain, resulting in a wide variety of dangerous effects. Any drug which qualifies as a hallucinogen has the potential to cause visual, auditory and sensory hallucinations or create a sense of detachment from space, time and one’s physical body. Certain substances within this category can cause both these effects. Hallucinogens may also have a depressive or stimulating effect on the central nervous system, resulting in any of the symptoms discussed in the above two sections – these are wildly unpredictable drugs!

Hallucinogens can put a great deal of strain on cognition and are known to cause permanent psychological damage and psychosis in certain people. Taking a hallucinogen and driving would likely result in extremely dangerous driving behavior. You may not be able to tell the difference between hallucinations and reality and could perform risky maneuvers while trying to avoid imagined dangers.

Over-the-counter and prescription drugs

Even drugs that have commonly accepted medical uses can seriously impair your driving ability and threaten your health. Every medication – whether it is used to treat a headache, chronic pain, depression or insomnia – has the potential to cause side effects. Common side effects include drowsiness, vision disturbances, poor muscle coordination, anxiety, restlessness and dozens of other undesirable effects that can change your driving behavior and impair your vehicle control skills.

It is important to keep in mind that people respond to drugs differently. Your doctor or a pharmacist may advise you that it is acceptable to drive while taking a certain medication but the final judgment on whether to get behind the wheel must come from you. When taking any drug, you must monitor yourself for changes in your physical and mental state to ascertain whether you can safely drive. If your driving ability is noticeably impaired and a police officer pulls you over, you will be charged with driving while intoxicated even if the drug you are taking is legal and has been prescribed by a medical professional.

Many drugs that are used to treat severe pain, anxiety, depression, ADHD and sleep disorders are chemically similar or identical to illegal stimulants and depressants. The only thing that separates these medications from illegal recreational drugs is the fact that they have been approved for medical use, are produced in accordance with safety standards and are measured into controlled doses. Prescription medications can impair your driving ability and damage your health just as much as illegal drugs, particularly if you use them irresponsibly.

Take opioid pain killers as an example. Prescription opiates such as codeine, oxycodone and fentanyl come from the same plant as heroin (or are made in a lab to be chemically similar) but are taken perfectly legally by millions of people around the United States every year. If you misuse a prescription opiate (either by taking it without a prescription or exceeding the stated dose), you may as well be using heroin, as the danger you expose yourself to is the same. Even when prescribed and used in absolute accordance with the instructions, these powerful pain killers can blur your cognition, cause drowsiness and slow reaction time. Remember that your body reacts to chemical substances indiscriminately – it does not care whether you are using a drug legally, or illegally.

In the module on prescription and over-the-counter drugs, we’ll introduce you to some of the main medications to be wary of, along with their likely effects on your driving ability.

Inhalant abuse

Next up, its time to address a group of commonly misused substances that do not fit into any category of drug we have discussed so far, as they were never designed for human consumption. Hair sprays, body sprays, paint, paint thinner, lighter fluid, marker pens, glues, nail polishes and dozens of other everyday household products contain psychoactive chemicals that alter the normal functioning of the brain when their fumes are inhaled. These “inhalants” are widely abused by younger teenagers who cannot easily access other recreational drugs.

It is almost impossible to predict how a person will react to abusing an inhalant, as these products typically contain dozens of dangerous and potentially deadly psychoactive substances. Some of the most frequently occurring chemical ingredients and their effects are listed in this article. They range from loss of sensation and poor coordination to blackouts, heart damage and sudden death.

Many of the chemicals within inhalants can hang around in your body for a long time after the initial effects of the substance have worn off. Days or even weeks after abusing an inhalant, the user may experience sudden, unexpected and debilitating side-effects. If this were to happen while you were driving, the result would likely be catastrophic.

The dangers of drug interactions

Drugs work by interacting with the chemicals in your central nervous system. If you were to take two or more drugs at the same time, they would also interact with each other, resulting in a different effect on your body. Drug interactions can be extremely dangerous and often increase the risk of driving impairment and overdose. The results of a drug interaction depend on the main biological action of the drugs involved and the length of time it takes each substance to take effect and wear off. For example:

  1. 1

    Two drugs with the same action (i.e. two stimulants or two depressants).
    The drugs would work with each other, resulting in a stronger overall effect. The user’s central nervous system would be twice as stimulated, or twice as depressed, resulting in a much greater chance of overdose.

  2. 2

    Two drugs with different actions (i.e. one stimulant and one depressant).
    The drugs would work against each other. The user may feel less intoxicated as the substances balance each other out. However, taking two drugs with opposing functions (e.g. alcohol and cocaine) dramatically increases the chance of negative side-effects occurring. Plus, the user may take more of the substances in question, as they are not fully experiencing their effects. If one substance were to wear off before the other, the risk of overdose is considerable.

The task of filtering all intoxicating substances from your blood falls to the liver. If you take two substances at the same time, the liver will have to work twice as hard, meaning that:

  • It will take longer for the liver to do its job, leaving you intoxicated for longer.
  • The liver will be more susceptible to tissue damage.

Any drug combination can be dangerous, even mixing alcohol with over-the-counter medication. Alcohol is the substance most commonly used alongside prescription and recreational drugs, as most people tend not to think of it as a drug and therefore do not recognize the danger it poses. Drinking alcohol can lead to profound driving impairment and damage to your health all by itself. When combined with other drugs, the result is often deadly. Find out how your body, mind and driving ability will likely suffer as a result of common drug interactions here.

Drugs and your driving ability

Your ability to drive safely depends on being able to see what is going on around your vehicle, process information and operate the car’s controls effectively. This demands good vision, clear cognition and good motor skills. An effective dose of any drug will disrupt each of these skills and make you a less safe driver. In the case of many prescription medications and recreational substances, your vision, thought processes and muscle coordination will be impaired to such a degree that you will be completely incapable of driving defensively and avoiding roadway conflicts.

Looking at national drug-impaired traffic accident data, there are clear correlations between the causes of collisions and the substances involved. Drugs within a particular category (stimulants, depressants or hallucinogens) lead to similar driving impairments and often result in the same type of crash. For instance:

  1. 1

    Stimulants cause restlessness, anxiety, aggression, over-confidence and shaking. This often leads to tailgating, speeding, disregard of road laws, erratic maneuvering and risk-taking behavior.

  2. 2

    Depressants cause drowsiness, poor coordination, mental confusion and memory impairments. This often leads to dangerously slow driving, weaving between lanes, sloppy maneuvering and irrational decision making.

  3. 3

    Hallucinogens may cause any of the above effects, plus hallucinations and a sense of detachment from reality. This often leads to complete disregard for road rules and roadway conditions, erratic changes in speed and extremely dangerous behavior (such as reversing along an expressway or attempting to make a U-turn in the middle of a busy highway).

Drug abuse is guaranteed to result in unsafe driving behavior while you are under the influence of the drug, and for some time afterward. If recreational drugs are a regular part of your lifestyle, you will never truly be fit to drive. You can drive while taking prescription drugs to manage pain or illness, with approval from your doctor. However, you must make yourself aware of the possible driving impairments the medication can cause, based on whether it has stimulant, depressant or hallucinogenic properties. That way, you can spot these impairments when they occur and stay out of the driver’s seat.

Remember that it is your responsibility to ensure you are mentally and physically fit to drive. The law does not distinguish between different types of drug impairment. If you cause property damage or harm somebody while impaired by ANY drug, you could be going to jail for a very long time.

Would you pass a driving test today?

Find out with our free quiz!


Like the article? Give us 5 points!

Click a star to add your vote

4.2 out of 5 stars based on 5 votes.

Read next

The Controlled Substances Act
Driving Under The Influence of Drugs 2 of 10

The Controlled Substances Act

The controlled substances act (CSA) was established to help the US government regulate the manufacture, importation, possession, use and distribution of drugs. It is federal legislation which applies everywhere in the United States. However, you should keep in mind that some state governments have passed their own laws regarding the possession, use and distribution of certain drugs.

Effect of Drugs on Your Driving Ability
Driving Under The Influence of Drugs 3 of 10

Types of Drugs and Their Effects

We will address the dangers of drug use and how specific substances will affect your ability to drive. Before we delve into specific drugs and their effects, let’s look at drug “types”. There are thousands of different drugs, each with a distinct chemical make-up that exerts a unique effect on human bodily functions.

Stimulants and Driving
Driving Under The Influence of Drugs 4 of 10

Stimulants and Driving

Stimulants are a category of drug that works on the central nervous system to “speed up” ordinary bodily functions. When you take a stimulant drug, you may experience short-term feelings of euphoria and a false sense of well-being. Higher doses of stimulants can result in anxiety, loss of focus, shaking, erratic behavior and violence.

Driving Under The Influence of Alcohol 7 of 12

Alcohol’s Effect on Cognition

Cognition is the mental process of collecting information, forming thoughts and making decisions based on what you know. If any aspect of the cognitive process is impaired by alcohol while you’re driving, you are likely to make unsafe decisions, endangering yourself, your passengers and all other road users nearby.

Driving Under The Influence of Alcohol 8 of 12

The Effects of Alcohol on Your Driving Skills

Your responsibilities as a driver and alcohol do not mix. You must do everything within your power to avoid injuring yourself, injuring other road users or damaging property. Even very small amounts of alcohol can impair your mental and physical driving ability and so you must not drink and drive.

Driving Under The Influence of Alcohol 9 of 12

Alcohol & Emotional Fitness

Experiencing an intense negative emotion will directly disrupt your ability to remain attentive while driving, affect the decisions you make in response to events on the roadway and alter your behavior towards other drivers. Drinking alcohol affects your emotional fitness both in the short-term and over time

Driving Under The Influence of Alcohol 10 of 12

Alcohol Poisoning

If your blood alcohol concentration surpasses a safe level, you can become dangerously ill very quickly. This is known as alcohol poisoning; it occurs when your liver is overwhelmed by the amount of alcohol in your blood and can no longer filter it rapidly enough to protect you.

Driving Under The Influence of Alcohol 11 of 12

Long-Term Impact of Alcohol

Alcohol is technically a drug in that it is a “substance which has a physiological effect when ingested or otherwise introduced into the body.” In addition to the obvious short-term negative impact, alcohol consumption can seriously damage your mind and body when used repeatedly over a prolonged period.

Driving Under The Influence of Alcohol 12 of 12

Alcohol Abuse and Addiction

In addition to making you unfit to drive, disrupting your mental health and wreaking havoc on your body, alcohol abuse will have a far-reaching negative impact on your life and future. People who consume alcohol irresponsibly often find themselves experiencing guilt, shame and confusion over things they did while drunk.