EducationWhat does THC do to the brain?

What does THC do to the brain?

7 min read

Lydia Kariuki

What does THC do to the brain?
Delta-9-tetrahydrocannabinol (THC) is a psychoactive molecule present in cannabis that affects key functions of the brain such as the state of consciousness, mood, memory, attention, learning, reaction time, and possibly even the formation of new brain cells. Traditionally, THC has been associated with the intoxicating, euphoria-inducing effects of cannabis, leading many to believe that it lacks therapeutic potential.


Thanks to recent research, we now know that there’s more to THC, and that there may be many potential therapeutic applications for this often misunderstood, even demonised cannabinoid. 

While research is happening, quite a number of the studies on cannabis are preliminary and hence there’s a lot of contradictory information. The evidence so far suggests that while THC may cause short-term adverse effects, the long-term effects are potentially therapeutic.

What is THC?

Delta-9-tetrahydrocannabinol (THC) is one of the hundreds of bioactive molecules that are present in medicinal cannabis. It belongs to a group of molecules known as phytocannabinoids and is one of the two most concentrated and researched phytocannabinoids. The other prominent phytocannabinoid is cannabidiol (CBD), but this molecule is non-intoxicating, unlike THC. THC was first discovered and isolated in 1964 by the late Professor Raphael Mechoulam.

THC and the endocannabinoid system

The endocannabinoid system is a dynamic biological system that is believed to maintain a state of physiological balance (homeostasis) in the body. It is composed of endocannabinoids, receptors, and enzymes. THC has been found to interact with a group of endocannabinoid receptors called CB1 receptors that are primarily located in the brain and spinal cord. THC is a partial agonist at CB1 receptors and has a high binding affinity for these receptors. This action is what potentially mediates THC’s psychoactive properties, and also its potential for medicinal applications.

The section below examines what THC does to the brain, from preliminary scientific evidence.

THC and euphoria

Euphoria is a state of extreme happiness or excitement and when it is triggered by cannabis it is commonly referred to as the “high.” THC easily crosses the blood-brain barrier to bind to CB1 receptors that are located in the brain. These are the same receptors to which anandamide, one of the endocannabinoids produced by the body (also referred to as the “bliss molecule”) binds. This is a possible explanation as to how THC is able to induce euphoric feelings.

Earlier on, it was believed that THC was the only cannabinoid that could induce euphoria. It has now emerged that other phytocannabinoids that are similar to THC, such as delta-8 and delta-10, can also cause euphoric states.

THC and the adolescent brain: memory, attention and learning

THC may cause short-term memory loss. Some early studies have found that THC interferes with how the hippocampus (the region of the brain that controls memory formation) processes information. Other studies have suggested that THC may trigger long-term memory loss, especially when THC exposure occurs during adolescence or even earlier.

THC use among adolescents has also been associated with impaired attention and learning. Even mild to moderate cannabis use in adolescence may cause changes in the brain which may bring forth such impairments.

Fortunately, most of the cognitive impairments are in the mild to moderate range. Of course, there are a few arguments countering the negative effects of THC on the brain. But as Dr Siegel, a clinical psychiatrist, puts it in this interview 

“The reality is that we’re always going to have these diverse views of cannabis until we invest in larger, more controlled research studies.”

THC and reaction time

THC intoxication has been linked to slower reaction times, or in other words, the time that it takes to respond to a stimulus. 

For example, how long does it take an intoxicated driver to step on the brakes or swerve the car to avert an accident? This may also be called a “crash avoidance reaction time.” However, this is not just restricted to driving; people operating heavy machines can also be affected.

A 2006 study showed a significant lag in reaction time, especially when higher doses of THC had been administered. This happens possibly because cannabis impairs one’s perception of time.

Have car crash fatalities increased in states with legal marijuana programs?

The evidence is contradicting.

It is difficult to draw a causal relationship between cannabis legalization and changes in car crash fatalities. In addition, it is even more difficult to ascertain if a driver is driving while intoxicated (with THC) or if they merely have residual THC in their system. There's a obvious need to invest in technology that not only tests for the presence of THC or its metabolite in the system, but that can actually detect cannabis impairment in real-time.

THC and neurogenesis

Until recently, scientists believed that new neurons could not be created after the developmental stage. Now we are aware that neurogenesis happens throughout the entire lifespan of humans, and in all mammals, not only humans. This realization has transformed our understanding of neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease.

THC has shown the potential in triggering the formation of new neurons in the brain, which is important for memory and learning. One lab study that was published in 2017 found that THC could enhance brain neurogenesis and improves cognitive function. This seems to contrast the evidence that cannabis use may cause cognitive decline. 

This paradoxical effect has been explained using the “biphasic theory”. At higher doses, THC may cause cognitive decline, but the opposite effect may occur at lower doses. In other words, lower doses of THC may improve cognition, learning, and even memory. Scientists are currently exploring the potential of THC in managing Alzheimer’s and Parkinson’s disease.

What about THC and creativity?

Creativity is difficult to quantify objectively. Some studies have opted to measure divergent thinking and found a negative correlation between cannabis use and creativity. However, THC has been constantly linked anecdotally to increased intuition and creativity. 

It has been reported that Steve Jobs once claimed that cannabis made him more relaxed and creative. One study found that software programmers turn to marijuana to boost their creativity. Jordana Wright interviewed a series of creatives including actors, comedians, painters, sculptors, writers, and musicians, all of who reported using cannabis to enhance their creativity.

Is marijuana (THC) a gateway to other drugs?

During the dark era of cannabis prohibition, the plant was touted as a gateway drug to the abuse of harder drugs. This implied that most people who abuse cannabis would end up abusing harder drugs. 

This has been linked to cannabis’ ability to alter the brain’s reward system and hence trigger impulsivity. However, there is no hard evidence showing that THC alters the brain in a way that makes the user more susceptible to addiction to other drugs. What is apparent is that, since cannabis is the most widely available illicit drug in many countries, it is often abused earlier by most people. And a person who has abused one illicit drug may be more likely to progress and abuse other illicit drugs in the future.

Is THC good or bad for the brain?

From preliminary research, it appears that THC may cause short-term impairment of memory and cognitive abilities, and may be more harmful to the developing brain. THC may also impair driving and lead to road accidents. However, lower doses of THC can potentially trigger neurogenesis and hence improve memory and learning; this is called the paradoxical effect of THC.

Generally, THC use in pregnancy and adolescence is discouraged because the long-term effects are uncertain. Though it is suspected that THC may have a role to play in treating neurodegenerative diseases such as Alzheimer’s and Parkinson's disease, more research is needed in this area.


At the end of the day, it is hard to provide a definitive, overarching answer as to whether THC is good or bad for the brain. But, the same can be said for many conventional pharmaceuticals, with some of these options offering far more severe side effects than medicinal cannabis. 

The effects seem to depend on several factors such as dose, age, and frequency of administration. As more research becomes available, we may be able to draw better conclusions about this complex topic. For now, it’s best to always consult a registered medical cannabis doctor before making any decisions about whether this exciting new treatment option is the right choice for you. 

Accessing medical cannabis can be challenging due to the stigma surrounding it. However, Releaf makes it simple with our tailored monthly packages, specialist consultations for medical cannabis, and a unique medical cannabis card for protection, all based on your cannabis prescription.

It is important to seek medical advice before starting any new treatments. The patient advisors at Releaf are available to provide expert advice and support. Alternatively, click here to book a consultation with one of our specialist doctors.

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Lydia Kariuki, a medical nurse and journalist with a diploma in clinical research, specialises in translating complex cannabis research into accessible content, fostering public understanding and awareness.

Our articles are written by experts and reviewed by medical professionals or compliance specialists. Adhering to stringent sourcing guidelines, we reference peer-reviewed studies and scholarly research. View our editorial policy.

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