Michael Hunter, MD on Medika Life

Does CBD Affect Your Cognition?

IF YOU TAKE CBD, I HAVE SOME NEWS FOR you regarding brain health: Driving ability and cognition are not affected by cannabidiol (CBD), even at very high doses. That’s the finding of a small pilot study from the University of Sydney (Australia).

Today we explore the findings of a randomized clinical trial that used simulated driving sessions for 17 participants taking CBD. First, however, let’s look at some cannabidiol basics and side effects.

Cannabidiol (CBD) basics

Cannabidiol (CBD) is a chemical in marijuana. CBD is different from the psychoactive ingredient in marijuana that induces a so-called high, tetrahydrocannabinol (THC).

Photo by Michal Wozniak on Unsplash

CBD comes in oil form, but it is also available as a vaporized liquid, an extract, and an oil-based capsule. Want to use CBD? You may find the product in food, drinks, and even beauty products.

Today, the only CBD product approved by the United States Food and Drug Administration is a prescription oil known as Epidiolex. State laws regarding cannabidiol use vary by state.

Cannabidiol (CBD) side effects

Researchers are exploring CBD as a management tool for various conditions, including anxiety, diabetes, multiple sclerosis, Parkinson’s disease, and schizophrenia. Efficacy data remains limited, and cannabidiol has potential risks:

  • dry mouth
  • diarrhea
  • diminished appetite
  • fatigue and drowsiness

CBD can also alter the effects of other medicines, including the common blood thinner warfarin, a heart rhythm medication known as amiodarone, the thyroid medicine levothyroxine, and several seizure medications (including clobazam, lamotrigine, and valproate).

The stated dose and purity levels of CBD in products are unreliable. A study of 84 CBD products purchased online showed that more than one-quarter contained less CBD than stated on the level. Moreover, 18 products had the psychoactive component, THC.

Cannabidiol (CBD) and cognitive function

Researchers conducted a randomized clinical trial involving simulated driving sessions.

Each subject, aged 18 to 65, did four treatment sessions and two simulated driving conditions. None had used cannabis for at least three months prior. The treatments consisted of oral CBD (15, 300, or 1500 milligrams) or a placebo. The subjects then had a washout period of at least seven days.

Photo by Evgeny Tchebotarev on Unsplash

Researchers then conducted a driving simulation at 45 to 75 and 210 to 240 minutes after consuming CBD. A second driving test coincided with peak blood levels of CBD concentrations (about three hours after consuming 25 mg or 300 mg of CBD and about four hours after the 1,500 mg dose).

The researchers checked the subjects’ cognitive function at baseline, before the first simulated drive, and before the second simulated drive. They also asked participants about their feelings (for example, do you feel sedated, stoned, alert, anxious, or sleepy?).

Finally, the scientists checked the participants’ cannabinoid concentrations, blood pressure, and heart rate while seated.

Here are the conclusions:

  • The 17 subjects appeared no more likely to weave or drive too close to a car in front of them (compared to those taking a placebo).
  • Even at high doses, CBD does not appear to induce feelings of intoxication or impaired driving performance.
  • CBD persisted in blood plasma for more than four weeks following the 1,500-milligram dose.

This small study indicates that a single dose of CBD did not impact specific driving aspects, at least in young, healthy adults.

My Take: Cannabidiol (CBD) and cognitive function

As more people turn to cannabinoids such as CBD for symptom relief, we will need more studies about the cognitive and real-world behavioral consequences of use.

While this study is reassuring that CBD use does not appear to impair driving, we need studies with larger sample sizes to understand the implications of CBD use better. I also worry about CBD’s interactions with other drugs.

And remember, CBD products have varying amounts of the psychoactive chemical THC. The current study examined the effects of pure non-plant-derived CBD. Finally, the research examined acute administration; we need studies examining chronic use’s implications.


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Michael Hunter, MD
Michael Hunter, MD
I received an undergraduate degree from Harvard, a medical degree from Yale, and trained in radiation oncology at the University of Pennsylvania. I practice radiation oncology in the Seattle area.

Michael Hunter, MD

I received an undergraduate degree from Harvard, a medical degree from Yale, and trained in radiation oncology at the University of Pennsylvania. I practice radiation oncology in the Seattle area.

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