Driving Under The Influence of Drugs
Prescription and Over-the-Counter Drugs

Prescription & Over-the-Counter Drugs: Driving Under The Influence

Updated Dec. 25, 2020

Whether or not a drug is legal has very little bearing on its ability to threaten your health, cause intoxication or render you an unsafe driver. Many prescription medications and over-the-counter (OTC) drugs can cause side effects that will impair your ability to drive safely. Furthermore, when taken long-term or at high doses, these legal drugs can cause health complications, overdose and death.

Taking any medication in a manner other than recommended by your doctor, pharmacist or the instruction leaflet that came with the drugs can produce a variety of dangerous effects. In some cases, even taking medication precisely as instructed can lead to unanticipated effects that would render a person unsafe to drive. For instance, certain medications can cause:

  • Drowsiness
  • Blurred or double vision
  • Light sensitivity
  • Heavy limbs
  • Nausea
  • Restlessness
  • Impaired focus

Despite the strict regulations controlling the legal drug formulations which are used in prescription and OTC medications, there is still an enormous potential for driving impairment when taking many common medicines. Medications to be wary of include:

  • Prescription drugs for anxiety
  • Antidepressants
  • Any product containing codeine
  • Allergy medications
  • Cold and flu remedies
  • Cough medicines
  • Pain killers
  • Tranquilizers
  • Diet pills and stimulants

While legal medications are arguably safer than illegal drugs, they will never be totally safe. The problem is that the precise effects of a drug depend on a variety of factors and are difficult to accurately predict. Dose, diet, lifestyle and the genetic make-up of the patient all play a part in how impaired they will be when taking a medication. One person may be totally fine to drive on a certain drug, while the same dose of the same drug renders another person completely unfit to drive.

For this reason, it is incredibly important that you pay attention to your own mental and physical condition when taking any drug that has the potential to impede driving ability, even if your doctor has told you that you should be safe to drive. Ultimately, it will be you – not your doctor – who will be held responsible should you hurt or kill another person while behind the wheel and impaired by a legal drug.

Prescription drugs, OTC medications & DUI

If your driving is noticeably impaired and you are found to be under the influence of certain OTC and prescription drugs, you could be prosecuted for DUI or DWI, just as you would be for driving under the influence of alcohol or an illegal drug. In most states, the law does not distinguish between legal and illegal drugs in DUI cases. To protect yourself from legal repercussions, be sure to carry the prescriptions for any medications you take while driving. If you are pulled over by a law enforcement officer and there are prescription medications in your vehicle, you may be asked to produce these documents.

The dangers of prescription medications

Prescription medications are particularly dangerous when not taken with caution. Remember that many legal prescription drugs are made using controlled quantities of illegal substances and can be incredibly harmful. For instance, the common pain medication codeine is an opiate, like heroin, with similar biological mechanisms and physical effects. Unfortunately, the “legal” status of prescription drugs often blinds people to the dangers involved in taking them.

Drugs that are available on prescription have recognized medical applications, but this does not make them any less dangerous than illegal drugs. In fact, many prescription drugs have a similar potential for physical or psychological dependency and abuse as illegal drugs with no medical applications. They are prescribed because a doctor believes that the potential benefit of using the drug outweighs the potential risk. This does not mean they cannot cause health problems or render a person unfit to drive, especially if the patient does not take them as instructed.

In the case of long-term use of addictive prescription drugs, the patient’s growing dependency on the substance can quickly surpass any responsibility they feel to use it wisely or concerns they may have for their own health. Of the 41,502 overdose deaths around the United States in 2012, over 53% were related to perfectly legal, pharmaceutical drugs.

Some of the most dangerous and frequently misused classes of prescription drug are:

  1. Opioids
  2. Central nervous system (CNS) depressants
  3. CNS Stimulants

Let’s talk about the risks involved in using these medications and the ways in which they can impair your driving ability.


Prescription medications based on opioids are predominantly used to treat chronic pain, which may or may not be associated with other medical conditions. There are an enormous variety of these opioid pain relievers available on prescription around the United States, each with slightly different effects and applications. As a nation, our reliance on opioid pain killers has grown steadily over the past couple of decades and shows no sign of slowing down. In 2012, 259 million prescriptions for opioid pain relievers were written across the country. This amounts to enough drugs for every adult in the United States to be given a bottle of pills. Here are some of the most common medications.

Common Prescription Opioids


Moderate to severe pain relief.


Moderate to severe pain relief. Less potent than morphine, with less of a sedative effect.


Treatment for heroin addiction.


Severe pain relief, twice as potent as morphine with stronger muscle-relaxing effects.


Severe pain relief, 80 to 100 times more potent than morphine.

Other common pain relievers derived from opioids include hydrocodone, hydromorphone, oxymorphone, meperidine and propoxyphene. One undesirable effect that all these drugs share is a high potential for physical dependency and abuse. They can also cause depressed breathing, dangerously slow heartbeat, coma and death. The risk of these more serious effects occurring increases dramatically when opioid pain killers are used in conjunction with CNS depressants or alcohol.

The short-term effects of taking any opioid painkiller – even at the recommended dose – include:

  • Severe drowsiness
  • Muscle weakness
  • Dizziness
  • Confusion
  • Poor coordination
  • Nausea
  • Itching

Prescription opioids and your driving ability

Research has demonstrated that opioids cause drowsiness and impair reasoning ability. Though there have been very few dedicated studies exploring the effects of opioid pain killers on driving ability, the data we do have suggests that driving under the influence of any opioid can double the risk of being involved in a collision.

Impairment by opioid pain killers can occur even at relatively low doses – it varies from person to person. Though all opioid painkillers have slightly different biological mechanisms and medical applications, the effects of impairment are very similar and will likely include drowsiness, mental confusion and poor coordination. While in control of a vehicle, these adverse effects can have catastrophic consequences. A person under the influence of opioids cannot pay full attention to the road and as a result, is likely to miss important visual details such as road signs, the presence of other road users and upcoming changes in roadway layout. They may also have trouble staying awake and could experience microsleeps.

The physical impairments caused by opioid intoxication are a recipe for sloppy maneuvering. A person under the influence of an opioid will have a longer overall reaction time and may fail to brake in a timely manner when presented with reasons to slow down or stop. Poor steering control may also cause them to turn too widely or meander out of their lane.

Central nervous system depressants

Depressants such as barbiturates, benzodiazepines and Z-drugs (non-benzodiazepines with similar effects) are often prescribed for sleep disorders, anxiety, panic attacks, seizures, restless leg syndrome and a variety of other conditions. These drugs are strictly regulated and only available via prescription as many of them can cause physical dependency and psychological addiction. With some, there is also a high potential for overdose when taken in a manner other than instructed or combined with alcohol.


Benzodiazepines are one of the most widely prescribed groups of drugs in the United States. They are also some of the most frequently misused. According to the National Survey on Drug Use and Health data from 2015 and 2016, around 30.6 million adults in the United States used benzodiazepines within that time period. Of that number, only 25.3 million had valid prescriptions for the drug, while 5.3 million misused it, having obtained it illegally.

Here are some of the most common benzodiazepines.

Common Prescription Benzodiazepines

Alprazolam (Xanax)
Chlordiazepoxide (Librium)
Clorazepate (Tranxene)
Temazepam (Restoril)
Diazepam (Valium)
Triazolam (Apo-Triazo, Halicion, Hypam or Trilam)

Benzodiazepines are powerful sedative drugs that can have immediate undesirable side-effects. At what dose these side-effects come about will vary from person to person depending on tolerance, genetic make-up and various other factors. They include:

  • Drowsiness
  • Confusion
  • Dizziness
  • Shaking
  • Poor coordination
  • Blurred vision
  • Extreme lethargy
  • Headaches


Barbiturates produce similar effects to benzodiazepines, though are prescribed less frequently as they are thought to have a greater potential for negative side-effects, abuse and overdose. Some common barbiturates are listed below.

Common Prescription Barbiturates


Unlike benzodiazepines, barbiturates are rarely prescribed for anxiety and sleep disorders. They are more frequently used in the treatment of epilepsy, seizures, head trauma, convulsions and severe migraines. The most common side effects to occur with barbiturate use are drowsiness and nausea. Though, patients may also experience:

  • Heavy muscles
  • Lack of coordination
  • Severe headaches
  • Confusion
  • Memory impairment
  • Slowed respiration


Z-drugs are non-benzodiazepine depressants commonly prescribed to treat sleep disorders. They are referred to as Z-drugs as all their names either begin with or contain the letter “z”. Some prominent medications in this group of drugs are listed below.

Common Prescription Z-drugs

Eszopiclone (Lunesta)
Zaleplon (Sonata)
Zolpidem (Ambien)

Most Z-drugs do not have the same anti-anxiety properties as other CNS depressants but exhibit a far greater sedative effect. Some side-effects caused by these drugs include:

  • Headaches
  • Dry mouth
  • Poor coordination
  • Impaired judgment
  • Hallucinations
  • Memory loss
  • Daytime sleepiness
  • Confusion
  • Complex sleep behaviors (sleepwalking, sleep eating and even sleep driving!)

Prescription CNS depressants and driving ability

All depressant medications slow down the central nervous system. While the side-effects vary from drug to drug, every medication within this category has the potential to cause extreme drowsiness, slowed movements and impaired cognition. Even when these side-effects are mild, they dramatically increase the likelihood that you will fall asleep at the wheel or fail to register important information about the roadway environment. In addition, your reaction time will be extended, and you may find yourself unable to respond to changes in the driving environment in time to avoid conflicts and collisions.

Z-drugs are known to seriously impair driving ability, even when only residual traces of the drug are in the driver’s system. These drugs often have a delayed effect, which can make it extremely difficult for a patient to determine whether they can safely operate a vehicle. Perhaps unsurprisingly, widely prescribed Zolpidem is among the most common drugs found in drivers who have been arrested for drug-impaired driving.

Central nervous system stimulants

Prescription CNS stimulants are frequently used to treat attention deficit hyperactivity disorder (ADHD), chronic fatigue, morbid obesity, narcolepsy and severe depression. Many potent stimulants can cause physical addiction and psychological dependence after just a few uses. Unfortunately, prescription CNS stimulants are frequently misused due to the energy boost and temporary “high” they provide. Patients develop a tolerance for most stimulants quite quickly, meaning that higher and higher doses must be taken to achieve the same initial effects.

Some of the most common CNS stimulants are listed below.

Common CNS Stimulants

Dextroamphetamine (Dexedrine)
Dextroamphetamine combined with amphetamine (Adderall)
Methylphenidate (Ritalin or Concerta)
Methamphetamine (Desoxyn)

A 2016 report published by the American Journey of Psychiatry found that over 16 million Americans over the age of 18 are using prescription stimulants. Worryingly, data collected from the same report also suggests that around 5 million Americans are illegally using prescription stimulants (with Adderall being one of the most commonly abused) for their performance-enhancing and weight-loss properties.

The side effects of prescription stimulants include:

  • Dizziness
  • Insomnia
  • High blood pressure
  • Fast, shallow respiration
  • Irritability
  • Depression
  • Anxiety
  • Paranoia
  • Headaches
  • Muscle spasms
  • Tremors
  • Mood swings and manic behavior

Prescription CNS stimulants and driving ability

Research conducted by the National Highway Traffic Safety Administration shows that low levels of CNS stimulants like amphetamines can improve drivers’ alertness and ability to react quickly. Unfortunately, the relatively low doses tested during the study also made drivers more likely to engage in dangerous or risk-taking behavior while behind the wheel.

At higher doses, the somewhat positive effects of CNS stimulants on driving ability disappeared and were replaced with considerably less favorable effects. While on high doses of stimulants, drivers exhibited loss of focus, slowed reflexes, loss of muscle control, poor motor skills, heightened anxiety and extended overall reaction time.

Abusing stimulants like Adderall, Concerta or Dexedrine may result in dangerous driving behavior. People intoxicated with these drugs often disregard right-of-way, ignore traffic control devices, drive at excessive speeds and fail to maintain a proper following distance.

The dangers of over-the-counter (OTC) drugs

Many drugs and common medications can be purchased without a doctor’s prescription. In some cases, there may be age-restrictions on certain drugs, or limits to the amount that any one person can purchase at one time. Drugs that are available over the counter usually have a very low potential for addiction and abuse. They often do contain harmful and intoxicating drugs but at relatively low and “safe” doses. Cough relievers, pain killers, allergy medication, stomach acid reducers and mild sleep aids can all be purchased over the counter, without a prescription.

Though OTC drugs are generally less dangerous than prescription-only drugs, they can still cause undesirable side-effects that can adversely impact your health and ability to drive safely. Usually, serious side-effects only occur when OTC drugs are taken at very high doses. However, some people may experience side-effects at relatively low doses if they are sensitive to a particular ingredient.

Always read the label of any OTC drug you are using and do not exceed the maximum dose stated on the packet. Remember that everybody responds to drugs differently. Even if the instructions on the packet suggest that you can drive while using the drug, pay close attention to your mental and physical well-being before doing so. If you feel impaired in any way, seek alternative means of transport.

Let’s check out the potential adverse effects of some common over-the-counter medications:

Pain killers

Low-strength pain relievers such as Aspirin, Tylenol and Advil can be purchased without a prescription. These drugs can relieve pain symptoms associated with headaches, muscle aches, dental problems and minor joint pain. They can also be used to reduce fever in people suffering from flu and other viral infections.

While OTC pain killers are relatively safe, they can be harmful when taken in large doses or used over an extended period. The long-term health risks associated with these drugs include blood thinning, increased risk of heart disease, heart attack and stroke, liver damage, stomach lining deterioration and light sensitivity. Taking well in excess of the recommended dose of any pain killer can be fatal.

While serious adverse side-effects from over-the-counter pain medications are rare, minor undesirable effects are relatively common and could very easily affect your driving ability. Common OTC pain reliever side effects include:

Experiencing any uncomfortable side effects would prevent you from fully concentrating on the driving task and increase your chances of making a fatal mistake behind the wheel. Always make sure you give pain relievers time to take effect before hopping into the driver’s seat, to make sure they will not hinder your ability to drive safely.


Antihistamines are a type of histamine-blocking drug, that inhibits your body’s inflammatory response to allergens, such as pollen, pet hair and dust. Their anti-inflammatory action also makes them useful in the management of cold and flu symptoms. Chlor-Trimeton, Benadryl, Unisom, Siladryl and Banophen are some well-known OTC antihistamines.

Many antihistamines have a powerful sedative effect and should be used with caution if you need to drive or operate heavy machinery. Other side effects include:

  • Muscle weakness
  • Nervousness or anxiety
  • Dizziness
  • Nausea
  • Restlessness
  • Vision disturbances (in severe cases)

As with over-the-counter pain relievers, it is important to gauge your physical and mental reaction to antihistamines before choosing to drive. Restlessness, anxiety and nervousness are relatively common side-effects. Even in cases mild enough not to be immediately noticeable, these effects could alter the way you make decisions behind the wheel, leave you more impatient and prone to driving aggressively.

Keep in mind that antihistamines often enhance the effects of other drugs and substances, such as alcohol. If you drink even a small amount of alcohol while taking antihistamines, you may find suddenly find yourself extremely impaired.

Cough medicine

The hallucinogenic drug dextromethorphan is the active ingredient in most over-the-counter cough medicines, such as NyQuil and Robitussin. It creates a similar chemical reaction to PCP when ingested. The amount of this drug used in OTC cough medicines is negligible. It is enough to create beneficial expectorant and cough-relieving effects, without also causing undesirable side-effects. However, taking more than the recommended dose of any cough medicine would increase the amount of dextromethorphan you are ingesting and could lead to dangerous effects. For instance, dextromethorphan is known to cause:

  • Hallucinations
  • Lack of focus
  • Seizures
  • A false sense of invulnerability
  • Violent behavior

Experiencing any of these effects while driving would lead to extremely dangerous behavior. Keep in mind that dextromethorphan has a stronger effect when combined with alcohol. Never drink alcohol when using over-the-counter cough medicines and always stick to the recommended dose. Make sure you are mentally and physically fit to drive before setting off on any journey while using a medication that contains dextromethorphan.

The dangers of drug interactions

All drugs (prescription, over-the-counter and illegal) produce mental and physical effects by creating a chemical reaction in the body. When a person is taking two or more medications at the same time, the drugs will interact with each other, potentially creating a different chemical reaction and thus, different effects.

It is important to keep in mind that just because a drug does not usually impair your driving ability, does not mean it will be equally as safe when taken in combination with another drug. Always check with your doctor or pharmacist before taking two medications together. In addition to rendering you unsafe to drive, mixing medications can create chemical reactions that seriously endanger your health. We discuss potentially dangerous drug combinations in more detail, in a later article.

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