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How does marijuana affect driving?

Marijuana – a cannabis product – is the most commonly used illicit drug worldwide. The use of marijuana is on the rise as more countries legalise its use.

Marijuana is also the most common illicit drug found in blood tests from impaired drivers. According to data collected by the US Trauma Centre, people who are involved in vehicle crashes and are tested for drugs, most frequently test positive for marijuana and alcohol. Young people are at a high risk of The risks of driving under the influence of marijuana These drivers are the most likely to use cannabis products recreationally and are also in an age group with a high risk of vehicle crashes. So, how does marijuana affect driving?

What is marijuana?

Marijuana is a product derived from the Cannabis sativa or Cannabis indica plant – one of the oldest known cultivated plants. The cannabis plant has more than 104 identified cannabinoids – the active ingredients of cannabis products – and  more than 400 other compounds.

One cannabinoid called tetrahydrocannabinol (THC) is believed to be primarily responsible for the psychoactive effects of the drug. Another active cannabinoid called cannabidiol (CBD) has received attention in research for its non-psychoactive properties and therapeutic potential for various neurological disorders and chronic pain.

The chemical make-up of a sample of cannabis is usually determined by the amount of THC and CBD. Potency is mostly attributed to THC concentration. Data from the US Drug Enforcement Administration (DEA) indicates the average potency of cannabis products has increased over the past decade.

Cannabis products are often categorized into three groups: herb (i.e., dried flowers), resin, and oil. The three forms of cannabis products usually differ in their THC content. Cannabis oil is usually the most potent form. Marijuana is often formed with the dried flowers, fruit, leaves, and stems.

There are a number of way to consume cannabis products. These can include smoking, eating or drinking, and vaporizing.  The time until the effects of the drug are noticed and the length of time they last will be different, depending on the method. For example, if marijuana is smoked, the THC is quickly absorbed into the bloodstream where it circulates throughout the body and the drug’s effects will be experienced soon after consumption. On the other hand, eating or drinking cannabis-containing products, such as edibles, will lead to a slower THC absorption into the bloodstream. In this case, effects will typically be delayed in comparison to smoking marijuana.

How marijuana affects driving

Marijuana and other cannabis-derived products act through the endocannabinoid system – responsible for regulating an individual’s appetite, blood pressure and sense of reward, among other functions. There are many cannabinoid receptors in the brain. This is where the interactions between the cannabinoids and receptors produce the main psychological effects of the drug. The exact mechanism of the drug’s action still needs more research.

The effects of marijuana include a feeling of euphoria and relaxation, changes in perception (e.g., of time), enhanced sociability, and an increased appetite. Other effects of the drug include impaired problem-solving and motor skills, decreased short-term memory, and altered visual perception. Some of these effects of marijuana can be problematic as they affect driving skills.

According to research, marijuana may affect important driving skills including reaction time, lane position, complicated tasks requiring divided attention, and road tracking. According to the National Institute on Drug Abuse, impaired motor functioning and altered mental state make driving under the influence of marijuana dangerous and increases the risk of being involved in a fatal crash.

Research has found that drivers with THC in their blood had a slower reaction time and were not able to stay within the lane compared to drivers without THC in their blood. Sudden obstacles or events resulted in more vehicle crashes for those driving under the influence of marijuana in driving simulation studies.

Overall, research indicates that certain automatic driving functions are impacted by low doses of THC. An individual is more likely to experience  even more driving impairments with a higher concentration of THC in their blood. The risks of driving under the influence of marijuana are increased when the drug and alcohol are both present in an individual’s blood.

Negative effects of marijuana

Consuming cannabis products, especially those with a high concentration of THC, can have a variety of negative effects. For example, dizziness, nausea, increased heart rate or dry mouth may be experienced. More serious negative effects can include a panic attack, which is the most commonly experienced emergency associated with consuming marijuana.

According to research it is possible to develop a marijuana use disorder, especially for those who started use in adolescence. Regular users of high potency marijuana are at a higher risk of developing temporary acute psychosis. For individuals with schizophrenia – a psychiatric disorder – long-term marijuana use may worsen their symptoms, such as paranoia and hallucinations. Frequent smokers of marijuana may experience breathing problems and be at a higher risk for developing lung infections.


Hartman, R. L., & Huestis, M. A. (2013). Cannabis effects on driving skills. Clinical Chemistry59(3), 478–492.

Lafaye, G., Karila, L., Blecha, L., & Benyamina, A. (2017). Cannabis, cannabinoids, and health. Dialogues in Clinical Neuroscience19(3), 309–316.

National Academy of Sciences. (2017). Health effects of cannabis and cannabinoids: The current state of evidence and recommendations for research. Retrieved from

National Institute on Drug Abuse. (2020). Marijuana research report. Retrieved from

Ogourtsova, T., Kalaba, M., Gelinas, I., Korner-Bitensky, N., & Ware, M. A. (2018). Cannabis use and driving-related performance in young recreational users: A within-subject randomized clinical trial. Canadian Medical Association Journal6(4), E453–E462.

Sewell, R. A., Poling, J., & Sofuoglu, M. (2009). The effect of cannabis compared with alcohol on driving. The American Journal on Addictions18(3), 185–193.

Turner, A. R., & Agrawal, S. (2020). Marijuana. Retrieved from

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