Driving Under The Influence of Drugs
The Effects of Combining Drugs & Alcohol

Combining Drugs & Alcohol: Driving Under The Influence

Updated July 22, 2019

Taking two or more drugs at the same time is incredibly dangerous, as one substance will interfere with the way your body responds to the other – and vice versa. The results of combining different drugs (including alcohol) are difficult to anticipate and can often be life-threatening. For instance, if you were to mix two substances which have similar effects on the central nervous system (e.g. two stimulants, or two depressants) the overall risk of overdosing is considerably higher than if you were to take two doses of a single substance.

While two substances with opposing effects (e.g. one stimulant and one depressant) would theoretically cancel each other out, taking two drugs with different functions still dramatically increases your risk of overdosing. When two different substances are working on your body at the same time, one may heighten the effects of the other by increasing blood flow to your brain. Alternatively, one drug could slow liver function to the extent that the other drug remains in your system for much longer than usual.

As soon as you mix one drug with another, your risk of dying from a drug overdose increases exponentially. Of the tens of thousands of overdose victims around the United States every year, a considerable number are found to have two or more substances in their bodies at the time of death.

The same is true of intoxicated drivers involved in fatal traffic collisions. Very often, toxicology reports show that the offending driver was under the influence of more than one substance when the crash occurred. Mixing different intoxicating substances has a profound detrimental effect on your ability to drive safely.

Taking more than one drug at a time will have one of three basic effects:

  1. 1

    An additive effect.
    When two substances have a similar biological effect, they will combine to create an effect that is twice as powerful.

  2. 2

    An antagonistic effect.
    When two substances have opposing biological effects, they will work against each other. The user may find the effects of both substances appear diminished. However, they will be more susceptible to negative side-effects and overdose.

  3. 3

    A synergistic effect.
    Two substances may react with each to create a faster or more powerful overall effect, greater than the individual effects of each substance added together. This is the case with many substance combinations.

Mixing alcohol with drugs

Alcohol is the substance most commonly combined with other drugs. When alcohol is used alongside prescription and over-the-counter medications, it can increase or decrease the effectiveness of the medication and create dangerous chemical interactions in the body. Using alcohol in conjunction with illegal substances is incredibly dangerous and unpredictable. The effects of mixing alcohol with illicit substances will vary dramatically based on the primary action and potency of the substance – the latter of which is very difficult to gauge when the substance in question is unregulated.

Mixing alcohol with stimulants

Stimulants such as cocaine, methamphetamine, Adderall (amphetamine and dextroamphetamine) and Ritalin (methylphenidate) speed-up the brain and the central nervous system. Whereas, alcohol is a central nervous system depressant which slows everything down. While you might think that taking two substances with opposing actions would lead to a lesser overall effect from both drugs, this tends not to be the case. The interaction between alcohol and common stimulant drugs often increases the side-effects associated with both substances. The presence of alcohol in the liver will also slow-down the rate at which the stimulant can be expelled from your body, increasing the risk of overdose.

Alcohol and prescription stimulants

Drinking alcohol while using prescription stimulants such as Adderall will dramatically increase the chances of experiencing serious side-effects, such as heart problems, stroke or seizures. Combining even a very small amount of alcohol with these medications will likely cause anxiety, nausea, dizziness and loss of coordination. Taking amphetamines or similar medications while drinking alcohol also substantially increases the risk of alcohol poisoning, as people tend to drink more while under the influence of stimulants.

Driving while under the influence of alcohol and prescription stimulants may lead to:

Alcohol and cocaine

People who take cocaine while drinking alcohol entertain a 20 times greater risk of sudden death from overdose, as compared to using either substance on its own. Alcohol also appears to enhance the mood and behavior-related side -effects of cocaine abuse. While under the influence of both substances, you will be particularly susceptible to sudden mood swings and violent, unpredictable behavior. An additional risk associated with mixing cocaine and alcohol comes from the combined chemical reaction of the two substances in the liver. When your liver processes alcohol and cocaine together, it produces a toxic substance called cocaethylene, which places great strain on all the body’s organs and increases the risk of them failing.

Driving while under the influence of alcohol and cocaine may lead to:

Alcohol and methamphetamine

Alcohol and illegal methamphetamine together are one of the most dangerous substance-combinations. Despite being more intoxicated due to the combined effect of both drugs, you will feel generally less intoxicated. This usually leads to taking more of both substances to maintain a consistent high, dramatically increasing the risk of overdose. Like cocaine, methamphetamine can produce extremely violent and unpredictable behavior when combined with alcohol.

Driving under the influence of alcohol and methamphetamine may lead to:

  • Road rage
  • Excessive speeding
  • Deliberately dangerous behavior, such as ramming other vehicles
  • Inability to perform even the most basic maneuvers
  • Complete disregard of right-of-way
  • Ignoring traffic control devices
  • Complete loss of vehicle control

Mixing alcohol with depressants

Alcohol is a central nervous system depressant. Combing alcohol with other depressants such as benzodiazepines, barbiturates and sedatives will therefore create a heightened and extremely dangerous depressant effect on the brain and body. Unfortunately, many people who take prescription depressants for anxiety, sleep problems and other disorders also drink alcohol as a way of self-medicating and alleviating the symptoms of their condition. This can produce a whole host of life-threatening short-term and long-term effects, including:

  • Dangerously low blood pressure and slowed heart rate
  • Extreme drowsiness
  • Unconsciousness
  • Slurred speech
  • Impaired vision
  • Extremely impaired coordination and motor skills
  • Nausea and vomiting
  • Coma
  • Death

As we mentioned earlier, taking two different depressants usually creates a more powerful effect than taking two doses of the same depressant. The risk of overdose is extremely high when combining alcohol with other depressant drugs, even when a relatively small amount of each substance has been consumed.

Driving under the influence of alcohol and depressant drugs can lead to:

  • The inability to coordinate steering and pedal control
  • The inability to sit up properly in the driver’s seat
  • The inability to perceive and respond to hazards appropriately
  • Extremely slowed reaction time
  • Falling asleep at the wheel

Alcohol and opioids

Opioids such as heroin, morphine, codeine, hydrocodone and oxycodone are another type of central nervous system depressant that are extremely dangerous when mixed with alcohol. The “double-depressant” effect which occurs when opioids and alcohol are used together is particularly potent and can result in extreme mental and physical impairment. People who combine opioids and alcohol often experience:

  • Low blood pressure and slow heart rhythm
  • Cardiovascular instability
  • Nausea and vomiting
  • Complete lack of inhibitions and inability to recognize risk
  • Abnormal behavior
  • Extreme dizziness
  • Complete loss of coordination and motor skills
  • Respiratory arrest
  • Loss of consciousness
  • Coma
  • Death

Irreparable brain damage is an extremely common side-effect from alcohol and opioid abuse. Due to the combined depressant effect of these two substances, breathing and heartbeat are slowed to such a degree that the body becomes starved of oxygen, causing brain tissue to shut down. Taking opioids and alcohol together will result in severe loss of balance, coordination and other motor skills, making everyday activities extremely dangerous.

Driving under the influence of alcohol and opioids can lead to:

  • The inability to control speed
  • The inability to steer the vehicle or remain within a lane
  • The inability to maintain proper posture in the driver’s seat
  • Forgetting to wear a seat belt
  • Extremely impaired perception of events around the vehicle
  • Loss of consciousness at the wheel

Mixing alcohol with hallucinogens

Hallucinogens are a diverse group of psychoactive substances capable of causing hallucinations and a sense of dissociation from one’s own body. Drugs within this group include LSD, Marijuana, PCP and Ketamine. The effects of combining alcohol with a hallucinogenic drug vary wildly from case to case, based on the type of drug involved and the mental state of the person using it. The chances of experiencing frightening hallucinations and other negative side-effects increase dramatically when mixing alcohol with any hallucinogenic drug.

Alcohol and marijuana

Combining alcohol with marijuana is likely to result in an array of negative physical side-effects, including nausea, vomiting, dizziness and a feeling of extreme intoxication. As marijuana suppresses the gag reflex, users who combine the drug with alcohol may be left unable to vomit and thus more at risk of alcohol poisoning. The hallucinogenic and dissociative effects of marijuana are likely to be more severe when the drug is used in conjunction with alcohol and can be extremely distressing.

People under the influence of alcohol and marijuana often suffer extreme paranoia, cognitive impairment, the inability to engage with their immediate environment and disconnection from time and space. Very few other substance combinations have the potential to impair driving ability quite so profoundly as these two drugs.

Driving under the influence of alcohol and marijuana can lead to:

  • Difficulty gauging space in moving traffic and difficulty reacting to visual cues (both of which lead to a strong chance of errors being made when merging)
  • The inability to judge distance or maintain a safe space around the vehicle
  • Poor steering control
  • Sloppy maneuvering
  • The inability to understand visual information (such as road signs, traffic signals and other roadway details)
  • The inability to maintain a safe speed (often, users will drive far below an appropriate speed based on roadway conditions)
  • The inability to perceive or understand risks

Alcohol and LSD

Drinking alcohol and taking LSD is extremely risky, as the hallucinogen will superficially reduce the noticeable effects of the alcohol. The user will therefore feel more sober than they truly are and will be more likely to consume dangerous amounts of alcohol. This makes the risk of alcohol poisoning, overdose and death far greater.

Alcohol consumption also increases the likelihood that the LSD will cause a “bad trip”, where the user experiences very distressing hallucinations. Studies have also shown that alcohol will affect the way a user recovers when LSD starts to wear off. The “crash” you experience after the initial effects of the drug subside will last longer and be more severe when alcohol is involved. This is often accompanied by nausea and vomiting.

Mixing alcohol with LSD seems to increase risk-taking behavior and lack of concern for personal safety, making it more likely that a person under the influence of these two substances will choose to get behind the wheel and drive. Due to the profound and often distressing hallucinations causes by mixing LSD with alcohol, this may result in:

  • Sudden swerving or braking to avoid imagined hazards
  • Weaving between lanes or completely disregarding road layout
  • Seeing other road users as enemies and attempting to harm them
  • Inappropriate use of in-car controls, pedals and steering
  • Driving far too slowly or speeding excessively
  • Driving in the wrong direction, against the flow of traffic

Alcohol and ketamine

Drinking alcohol increases the hallucinogenic and dissociative effect of the drug ketamine. Users are more likely to experience frightening hallucinations and will suffer extreme physical impairment. Ketamine numbs the body, impairs coordination and gives users a sensation of having heavy, unresponsive muscles. This affect will be considerably more severe when alcohol is consumed in conjunction with the drug. While in this condition, it is highly unlikely you will be able to get into your car – let alone drive it safely.

Driving while under the influence of alcohol and ketamine can lead to:

  • The inability to sit up in the driver’s seat
  • The inability to fasten your seat belt
  • An extremely poor view of the road, due to slumped posture
  • Difficulty reach pedals and other in-car controls
  • The inability to apply appropriate pressure to the pedals and steering wheel
  • Sudden swerving or braking to avoid imagined hazards on the road
  • The inability to maintain space around the car or remain in your lane
  • The inability to remain focused on the driving task or understand events on the roadway around you

Alcohol and psilocybin mushrooms

Drinking alcohol while taking of psilocybin mushrooms will lead to a heightened hallucinogenic affect. Initially, the alcohol may appear to calm paranoia and other negative side-effects from the mushrooms. Though as the user becomes more intoxicated, their hallucinations often become very distressing and can lead to extreme risk-taking, violent behavior, self-harm and suicide.

Driving while under the influence of alcohol and psilocybin mushrooms can lead to:

  • Sudden swerving or braking to avoid imagined hazards
  • Overreacting to minor dangers due to extreme paranoia
  • Aggression towards other road users
  • Difficulty interpreting traffic control devices
  • The inability to make sense of events around your vehicle
  • Deliberate acts of self-endangerment, such as driving into objects or off the side of the road at speed

Mixing alcohol with over-the-counter medications

While the dangers of mixing alcohol with illegal drugs or prescription-only medications may seem obvious, many people wrongly assume that drinking alcohol while taking over-the-counter medications is safe. After all, these drugs are readily available and can purchased without approval from a medical professional. Remember that over-the-counter drugs are still drugs. They create a chemical reaction in the body which can be extremely dangerous when alcohol is added into the mix.

Drinking alcohol while taking many over-the-counter medications can lead to organ damage, extreme drowsiness, heightened alcohol intoxication, heart problems and a whole host of other undesirable effects. Even when the interaction is not particularly dangerous, the presence of alcohol in your bloodstream renders many common OTC remedies completely ineffective.

Alcohol and non-steroidal anti-inflammatory drugs (NSAIDs)

Over-the-counter anti-inflammatory pain killers such as acetaminophen, aspirin and ibuprofen do not mix well with alcohol. These drugs already have the potential to cause digestive issues such as stomach cramps, ulcers, liver damage and damage to the stomach lining when taken on their own. These adverse side-effects are more likely to occur when the drugs are taken with alcohol. In addition, the risk of overdosing on NSAIDs is considerably higher when alcohol is already in the bloodstream and putting strain on the liver.

Alcohol and allergy, cold and flu medications

Many people rely on OTC antihistamines such as Benadryl, Zyrtec and Claritin to alleviate the symptoms of dust, pet and pollen allergies. Many of the active ingredients in these medicines are also present in common cold and flu medications. Unfortunately, these medications can be incredibly harmful when combined with alcohol – which is something very few people stop to consider. Most antihistamines are mild central nervous system depressants, just like alcohol. This means that drinking while using an allergy medication can have a potent depressant effect on the body, which may include:

  • Extreme drowsiness – making driving particularly dangerous
  • Dizziness
  • Loss of consciousness
  • Dehydration
  • Liver damage – especially in older adults
  • Memory impairment
  • Increased risk of dementia

Alcohol and cough medicine

Alcohol should never be mixed with over-the-counter cough syrups, as many of these medications contain alcohol anyway. Drinking while using a cough medication will likely result in severe intoxication. Most over-the-counter cough syrups are based on the active, cough-suppressing ingredient dextromethorphan, which also happens to be a potent hallucinogenic drug. A single dose of cough syrup does not contain enough dextromethorphan to cause intoxication or hallucinations, however, alcohol enhances the effect of the drug. If you consume alcohol while taking a cough medicine, you could experience visual hallucinations, confusion, extreme intoxication and drowsiness. Never mix the two substances.

Alcohol, over-the-counter drugs and driving ability

The interactions between alcohol and most OTC medications are significant enough to impair your driving ability. Remember that any mental or physical impairment – however minor – will render you less capable of controlling your vehicle and responding to changes on the roadway in a timely and effective manner.

Driving while taking over-the-counter medications and drinking alcohol can lead to:

  • Slower overall reaction time
  • Difficulty focusing on the task of driving
  • Feeling sleepy or falling asleep at the wheel
  • Difficulty processing visual information and making decisions
  • Poor speed control and sloppy maneuvering

As a driver, you are legally obligated to ensure you are mentally and physically fit to drive every time you get behind the wheel. Always read the label of any OTC medication you are taking and monitor yourself closely for any undesirable side-effects which may render you unsafe to drive. Under no circumstance should you drink alcohol while using any OTC drug or prescription medication – especially if you intend to drive. You may believe that you are under the legal BAC limit and feeling perfectly fine, but keep in mind that the presence of other drugs in your system may increase your alcohol absorption rate or prevent your liver from eliminating alcohol effectively.

The effects of different drug combinations

Using any combination of illegal drugs, prescription drugs or over-the-counter drugs will produce an array of unpredictable and often dangerous results. Taking multiple drugs at the same time is known as poly-drug use. People who engage in poly-drug abuse often do so for recreational or self-medication purposes. While different types of drug interact with each other differently, combining any two drugs is likely to heighten the harmful effects of both substances.

Let’s look at the risks associated with some common drug combinations.

Heroin and cocaine

Combining heroin with cocaine is dangerous recreational practice known as “speed balling”. As heroin is a depressant and cocaine is a stimulant, users believe they can mix the substance to balance their experience. Speed balling carries an enormous risk of overdose and death, as cocaine puts strain on the heart while heroin slows down respiration. As heroin’s effects generally last longer than cocaine’s, the user may be overcome by the heroin when the cocaine wears off.

Taking heroin and cocaine (or any other powerful stimulant) together often leads users to feel less intoxicated than they truly are. As a result, they may believe that they are capable of driving safely. Getting behind the wheel while under the influence of heroin and cocaine would be incredibly stupid. You may feel relatively sober to begin with, but as soon as the cocaine begins to wear off the depressant effect of the heroin will take over and you will suddenly become extremely impaired.

Cocaine and marijuana

This is another depressant-stimulant combination that can produce extremely dangerous results. As depressant-like marijuana will seemingly reduce the effects of the cocaine, the user may risk overdose by taking more of the stimulant. Studies have shown that the combined effect of marijuana and alcohol can lead to dangerously high blood pressure, rapid heart rate and irregular heart rhythm.

Let us not forget that cocaine can cause aggression and marijuana is a hallucinogen. If a user experiences paranoia, anxiety or hallucinations as a result of the marijuana, they are more likely to act out and behave in a way that endangers themselves or somebody else, if they also have cocaine in their system. This drug combination has great potential to cause aggressive, risk-taking driving behavior.

Marijuana and opiates

Marijuana can seriously threaten your health when combined with prescription opioids such as oxycodone, or illicit opioids like heroin. As both drugs exhibit a depressant effect, the user is likely to experience extreme physical and mental impairment. Body temperature may drop significantly, while heart rate and breathing will slow. In addition, they may hallucinate and suffer from acute mental confusion.

Using marijuana and opiates at the same time would render you totally unfit to drive. Your cognition would be impaired to the degree that you would be incapable of calculating risk or making safe decisions in response to changing conditions.

Beware of drug interactions

As a driver and a responsible young adult, you must be aware of the possible interactions between different substances you may choose to put in your body. You need this awareness to ensure you are always fit to drive, but also, to protect your physical and mental health. Never take so much as an aspirin without first considering whether anything else in your system may create an adverse reaction. Most prescription and over-the-counter medications are safe, if you read the warning label on the packet and take them exactly as directed. Even then, you must remain vigilant for unexpected adverse effects.

Using drugs recreationally and drinking alcohol is a different story. There will never be a totally “safe” way to mix different substances, as many recreational drugs are extremely dangerous on their own. Armed with the information in this article, you can be aware of the risks and make sensible, informed decisions before choosing to take any drug or consume alcohol. If you do take the risk – stay out of the driver’s seat!

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