Does Marijuana Boost Brain Power or Harm It?

Author Aleph One
14 March 2024
Learn what the latest research has to say about the impact of marijuana on the brain
14 March 2024
31 min read
Does Marijuana Boost Brain Power or Harm It?

Read more
  • 1. Turning the tide: new research suggests marijuana may lower subjective cognitive decline
  • 2. Weed is wasted on youth
  • 3. A side note: why does cannabis affect the brain at all?
  • 4. Short-term and long-term effects
  • 4. a. Acute impairment
  • 4. b. Long-term consequences
  • 4. c. Changes in brain structure
  • 5. Too few human studies
  • 6. Bottomline: should you be worried?

There’s no question marijuana directly impacts our brains and changes our ability to solve life’s simple puzzles on autopilot. Remember the first time you got high on weed? Remember the familiar streets of your own city suddenly turning into a maze? Or that helpless lull in a conversation when you forget what the hell you and your friends were just talking about?

No wonder science has so far mostly studied cannabis for its ability to make you dumber and not the other way around. Well, the situation’s starting to change. There’s still a lot we don’t know about marijuana’s impact on our cognitive function, but those who can’t imagine their lives without this substance or who use it medicinally can finally breathe a sigh of relief… and then make another toke. Hopefully, it won’t bring you one step closer to senility.

Turning the Tide: New Research Suggests Marijuana May Lower Subjective Cognitive Decline

In a surprising twist, a new study has suggested that marijuana use may be associated with lower odds of subjective cognitive decline (SCD), challenging popular assumptions. The study, published in the journal Current Alzheimer Research, found that recreational cannabis use is "significantly" linked to lower SCD, with users reporting less confusion and memory loss compared to non-users.

For this study, 4,744 adults aged 45 years and older were questioned about their marijuana use in the previous 12 months. The researchers can only speculate about the reasons why recreational consumption seems to have a protective influence over the human brain.

One possible explanation, as the authors note, is that cannabis use improves the quality of sleep and lowers stress levels, and both these factors are critical for mental health. It remained unclear whether researchers took into account the age of the respondents. It’s well known that cannabis use is more widespread among younger cohorts, and one would expect that younger respondents had experienced less confusion and memory loss compared to their older counterparts. One would also expect that the same younger group had more recreational cannabis smokers among them.


Cognitive Function Primary Brain Region
Attention Prefrontal cortex, parietal lobe
Perception Occipital lobe (vision), temporal lobe (hearing), parietal lobe (touch)
Memory Hippocampus, amygdala, prefrontal cortex, temporal lobe
Learning Hippocampus, amygdala, prefrontal cortex, basal ganglia
Language Broca's area, Wernicke's area, angular gyrus
Executive functions Prefrontal cortex
Problem-solving Prefrontal cortex, parietal lobe
Creativity Prefrontal cortex, temporal lobe, limbic system
Emotional processing Amygdala, prefrontal cortex, insula
Social cognition Prefrontal cortex, temporal lobe, amygdala, superior temporal sulcus

Some cognitive functions that our brain has.

Also interesting is the fact that medicinal consumption, even if combined with recreational one, was very weakly associated with reduced cognitive decline. Again, the possible explanation is that older and less healthy individuals, who had to use marijuana medicinally, also were those who had cognitive issues more often on average.

Beyond the reasons for cannabis use – medical vs non-medical – the study also looked at the frequency and the method of consumption. They found that more frequent use, as well as smoking as compared to vaping or edibles, both showed a very weak increase (they called it statistically insignificant) in self-reported mental issues.

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Weed is Wasted on Youth

Those acquainted with the topic didn’t miss one crucial feature of this study: it only looked at persons who are middle-aged or older. Why is it important? Because a growing body of research suggests that it actually matters at what age a person starts their acquaintance with weed.

Teenagers and young adults, especially those who develop a cannabis use disorder, miss out on a lot of things in life, including education, career, meeting lots of new people and traveling to lots of places. For older people, on the other hand, cannabis use may give a new vantage point, allowing them to look at things from a fresh perspective or break out from the vicious cycle of established thought patterns.


Does Marijuana Boost Brain Power or Harm It? A young woman enjoying a joint

Weed smoking is associated with young age, but it's older folks who could really benefit from it.

There’s a handful of studies suggesting that early exposure to marijuana does lead to various deficits of memory and cognition in later life. A 2007 rat study found that “exposure to cannabinoids during early stages of brain development can lead to irreversible, subtle dysfunctions in the offspring.” Another study from 2005 demonstrated that prenatal use of a synthetic cannabinoid, which binds to the same receptors as THC, lead to “the learning deficit and decreased emotional reactivity observed in the offspring.” Yet another series of experiments, this time done on monkeys, showed that “persistent effects of THC on cognitive abilities are more evident when exposure coincides with the developmental stage during which the underlying neural circuits are actively maturing.”

Moving beyond animal models, a report published in 2012 found cognitive problems in persistent cannabis users who began their heavy use in adolescence. Even those who quit smoking cannabis later in life did not fully restore neuropsychological functioning.

The problem with such studies is that they cannot establish whether marijuana use was the actual cause of cognitive decline or there was some underlying issue that led both to the cognitive decline and to the onset of marijuana use. For example, a lower socioeconomic background of a young person may lead to their poorer cognitive development and also make them more likely to abuse marijuana and start doing so at a younger age.

A Side Note: Why Does Cannabis Affect the Brain At All?

When you consume marijuana, a chemical compound called THC (delta-9-tetrahydrocannabinol) enters your body. THC is the main psychoactive compound in marijuana that gives you the high sensation. It works by mimicking the actions of natural neurotransmitters in your body called endocannabinoids, which are similar in structure.

Specifically, THC interacts with CB1 receptors. These are tiny proteins attached to your cells that receive chemical signals from different stimuli and help your cells respond. CB1 receptors are found predominantly in the brain and nervous system, as well as in peripheral organs and tissues.


Does Marijuana Boost Brain Power or Harm It? Synapses, CB receptors and cannabinoid molecules

This drawing shows ECS in action.

CB1 receptors are part of the endocannabinoid system (ECS), which is a complex cell-signaling system identified in the early 1990s by researchers exploring THC. This system plays a role in regulating a range of functions and processes in the human body, including sleep, mood, appetite, memory, reproduction, and fertility. The endocannabinoid system exists and is active in your body even if you don't use cannabis.

However, when THC interacts with ECS, it disrupts its normal functioning, leading to various effects such as altered senses, changes in mood, impaired memory, and in some cases, hallucinations. This interaction is what causes the psychoactive effects of marijuana.

Short-Term and Long-Term Effects

When studying the effects of marijuana on the brain, we should distinguish between acute effects, which are only noticeable while you’re actually high, short-term effects, such as your reduced ability to focus or lower motivation for hours or even days after the last use, and finally, long-term effects, which might persist indefinitely even if you have stopped smoking weed long ago.

Acute Impairment

No one would challenge the fact that being high on weed interferes with your ability to understand and remember things or make decisions. However, it’s equally evident that long-term users develop enough tolerance to counteract some of these effects. This subject is especially important for road safety: available research noted that people’s ability to drive safely when intoxicated depends on whether they’re casual or habitual smokers.

One study by Australian scientists assessed the cognitive abilities of cancer patients who use cannabis to relieve different symptoms. They were asked to consume marijuana in laboratory settings and then perform some cognition tests. As was expected, they didn’t show any statistically significant decline in their ability to reason, memorize, or make decisions – being long-term medical marijuana users, these patients had simply adjusted to being high.


Does Marijuana Boost Brain Power or Harm It? A young freckled woman's green eyes up close

It's usually first-time users who find marijuana incapacitating.

The Australian researchers also noted that in real-world scenarios, acute effects of marijuana are of even less importance, as most patients consume their medicine before sleep – when possible cognitive impairment doesn’t matter.

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Long-Term Consequences

Available research shows consistent measurable differences between smokers and non-smokers in terms of how they think. The real challenge is to clean the data from various confounding factors, such as use of alcohol and other substances, and also filter out possible underlying reasons such as genetics and socioeconomic status. When accounted for all this, the results are inconclusive at best.

One paper notes an association of worse verbal memory with the cumulative lifetime exposure to cannabis but no significant difference among past smokers and non-smokers in other domains of cognitive function. This study looked at 5115 persons aged 18 to 30 years at baseline and then followed them up over the next 25 years.

Another, 2015 study found no difference in IQs in pairs of twins if one of them was exposed to marijuana while the other wasn’t. Here, the genetic factor trumps marijuana use.

In its review of available literature on the topic, the National Institute of Drug Abuse acknowledges these inconclusive results and expresses hope that future studies will provide a more definitive answer. In particular, they look forward to an ambitious longitudinal study – Adolescent Brain Cognitive Development (ABCD) study – that will track young Americans from late childhood to early adulthood and see how cannabis use in some of them affects the very structure of their brains and whether they’ll end up different from their non-smoking peers.


Does Marijuana Boost Brain Power or Harm It? A person's hand as they show something on a brain scan, pointing it with a pen

Brain scans is the ultimate metrics that could shed the light on cannabis use and brain function.

Changes In Brain Structure

The same lack of conclusive evidence supporting either side of the argument is seen in the question of whether cannabis use leads to actual changes in brain morphology. Of special interest for researchers is the cortical surface, the part of the brain that is responsible for all higher functions associated with thinking, decision-making, and memory.

While previous research discovered some differences in the brain structure, a 2018 study found no evidence of that. The team looked at 141 cannabis users and compared them to 120 controls. They were interested in three characteristics of the brain’s cortical surface:

  • cortical thickness,
  • surface area,
  • and gyrification index,

and found no differences between users and non-users in any of the three.

Hopefully, the ABCD study mentioned in the previous section will shed light on this matter.

Too Few Human Studies

Looking at the available body of scientific evidence reveals a recurrent theme: there have been many animal experiments but very few human studies. This situation is likely to change, as more and more people are exposed to cannabis, particularly among medical patients. On one hand, this makes health professionals uneasy, as they suspect problems with public health down the road; on the other, it presents an opportunity to study the topic of cannabis use and brain function and probably come up with a definitive answer to the question: does weed make us more stupid or not?

Bottomline: Should You Be Worried?

We’re sure our readers value their intellects very highly and would hate to continue smoking cannabis knowing that it weakens their brain power. To them, we can offer consolation: the ‘devil’s lettuce’ isn’t as bad as propaganda has painted it for so many decades. But does it cause some harm, if even insignificant? We simply don’t know for sure. And by ‘we’, we mean science at its current state of the art.

While researchers are looking for a definitive answer, at least try to moderate your use and don’t allow it to become problematic and if you’re young and haven’t started your acquaintance with weed just yet, maybe take a raincheck until your brain is fully developed so as not to suffer from marijuana use or maybe even benefit from it.