CAN WEED MAKE YOU DUMB? WHAT SCIENCE SAYS ABOUT YOUR BRAIN

In 2018, President Trump quipped at a dinner that weed “does cause an IQ problem. You lose IQ points.” Former congressman and MSNBC host Joe Scarborough similarly opined, “Pot just makes you dumb.” While Trump and Scarborough aren’t exactly pillars of scientific truth, their remarks echo a common belief.

For decades, pop culture stereotypes, personal and racial biases, and old-school anti-cannabis propaganda have fueled the idea that weed lowers intelligence. But is it true? To answer, we first need to understand how cannabis affects your brain.

HOW CANNABIS AFFECTS YOUR BRAIN

Within the cannabis plant are hundreds of compounds called cannabinoids, terpenes, and flavonoids. The most famous of these cannabinoids are cannabidiol (CBD), which is non-intoxicating, and tetrahydrocannabinol (THC), which is psychoactive and intoxicating.

Cannabinoids affect your brain by binding to receptors and enzymes within and outside the endocannabinoid system, primarily CB1 and CB2 receptors. Because the endocannabinoid system helps regulate mood, memory, pain, appetite, and more, cannabinoids can have a wide range of physical and mental effects.

Psychoactive cannabinoids like THC primarily bind to your brain’s CB1 receptors, causing changes in memory, mood, coordination, and perception of time. In short, you get “high,” and the more THC you consume, the more intense these effects might be. CBD and similar C-like cannabinoids can slow down ECS enzymes and increase feel-good and body-regulating endocannabinoids.

Researchers also now recognize a larger network called the endocannabinoidome (eCBome), which includes additional brain receptors like TRPV1 and GPR55 that are directly targeted by THC, CBD, CBG, and more. Cannabis terpenes and flavonoids exert their neuroprotective effects and synergies with cannabinoids mainly in the eCBome.

These eCBome receptors help regulate brain signaling and influence memory and mood. That’s why cannabinoids influence more than emotions. They can also affect stress responses, learning, and even brain inflammation. In turn, these changes may shape how we focus, solve problems, store information, and even our overall cognitive ability.

In other words, cannabis doesn’t just tap into one switch in your brain. It interacts with a whole network of over 65 molecular targets that shape how your body and mind respond, producing effects that range from euphoric highs to deep introspection and relaxation.

That said, cannabis mind-altering effects may interfere with brain development in young people, much like alcohol. Since the brain isn’t fully developed until mid-to-late 20s, using cannabis before then can be risky.

BEING HIGH DOESN’T NECESSARILY MEAN BEING DUMB

The intoxicating effects of THC (being high) may last for two hours or more, depending on your dose, method of consumption, tolerance, and metabolism. While its effects last, you may act or speak in a manner some might call “dumb.”

Dumb in this scenario means being forgetful, incoherent, distracted, unmotivated, slow to respond, or easily amused. You may also have trouble problem-solving or completing tasks, since THC can temporarily disrupt short-term memory and executive functioning. That said, this cognitive hiccup typically lasts only as long as the high. Once THC’s effects wear off, your thinking and memory should return to their normal levels.

However, you should know that cannabis’s effects often vary depending on the strain, dose, and person. For most people, high-THC strains temporarily impair memory and focus. Others, though, find that well-balanced strains help boost creativity, elevate mood, or even sharpen focus. Some individuals get high and slip into a deeply philosophical mode, coming up with ideas you’d never expect from them.

In summary, high doses of THC may make you seem less mentally sharp for as long as the effects last. Terpenes like pinene can lend more mental clarity to particular strains. When balanced with other cannabinoids and terpenes, certain ingredients may support clearer thinking, lift your mood, or even spark creativity – while terpenes like myrcene may induce “couch-lock” or stupor associated with indicas.

CAN WEED MAKE YOU DUMB OVER TIME?

Some argue that long-term cannabis use may reduce intelligence, but the evidence isn’t conclusive. A 2025 cross-sectional study involving 1,003 young adults did find that heavy lifetime cannabis users showed lower brain activity during a working memory task.

But here’s the catch – the reduced activity occurred only in the parts of the brain linked to working memory. Plus, the study didn’t prove cannabis was the direct cause because it wasn’t placebo-controlled, and the findings only apply to the covered task and brain region.

Then there’s the 2021 study that linked adolescent cannabis use to poorer academic outcomes like lower grades, motivation, and GPA. However, after the researchers factored in genetics and environment, cannabis showed little lasting impact on cognition and mental health. The lower grades could just as easily have been due to complex socioeconomic and demographic factors, leading to skipping class or lack of motivation due to depression, rather than the drug itself.

Taken together, both studies suggest that reduced performance may stem from other influences – aging in the 2025 study and truancy in the 2021 study, rather than cannabis use alone. But assuming non-adults using cannabis increases the risk of cognitive issues, what about people who only started using in adulthood? Well, the evidence here is less clear, but new research is reassuring.

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Adult brains are more stable and less vulnerable to developmental disruption, so the same level of risk seen in teens (initiating before age 16) doesn’t necessarily apply. Some studies suggest long-term adult use may slightly affect memory, attention, or processing speed, but these effects are usually mild and often reversible after a period of abstinence. 

The latest research released this month directly challenges the notion of long-term brain harm in persons aged 18-25, as they show no greater long-term changes than those aged 25+. In fact, lifestyle factors like sleep, stress, and alcohol use tend to have a bigger impact on adult cognition than cannabis alone.

WHY DO SO MANY PEOPLE STILL BELIEVE WEED LOWERS INTELLIGENCE?

Several factors have helped keep alive the belief that cannabis lowers intelligence, from comments by public figures like President Trump to stoner portrayals in pop culture. For example, early 2000s comedies like “Dude, Where’s My Car?” or pretty much any older movie involving Seth Rogen. These stoner flicks helped shape public perception and cement the stereotype of the “dumb stoner.”

Of course, we can’t forget the infamous Afroman hit, “Because I Got High,” which is basically the weed anthem. With lyrics like, “I was gonna go to class before I got high… I coulda cheated and I coulda passed, but I got high… I’m taking it next semester, and I know why…” you can’t really blame people who believe cannabis makes you a little slower.

Propaganda from throughout the 1900s also played a role, with anti-cannabis campaigns that painted users as lazy, unmotivated, or even dangerous. Many boomers and Gen X have kept that gospel alive, sharing it with their kids, grandkids, and anyone who’ll listen.

Lastly, some people believe cannabis makes them dumber simply because of their own experiences. And since marijuana hits everyone a little differently, it makes sense that not all users have the same story to tell. Just look at these Redditors:

• Mephistophelesi: “I couldn’t write an essay without getting stoned recently for one of my certification exams. Having ADHD, my brain is like fuzz stuck on floating thoughts around my head, but when I get stoned, I can focus and not have a drifting thought.”
• InfoBarf: “Wish it worked like that for me. I just get real hungry and unable to do anything.”

SO DOES WEED MAKE YOU SMARTER INSTEAD?

I wish. But so far, there’s no overwhelming evidence that cannabis (or any of its compounds) can actually make you smarter. However, the right amount of THC might temporarily boost creativity, divergent thinking, or make certain tasks feel easier. The catch? These effects usually fade quickly and can flip the other way if you take too much, leading to fogginess or poor memory instead.

But there is good news – early research suggests that CBD might help reduce brain inflammation and improve memory and cognitive function as you age. Preclinical studies also support acidic cannabinoids like CBDA and THCA for reducing markers of Alzheimer’s, rescuing memory deficits, and preventing cognitive decline in mice. Other mouse studies show similar AD-prevention results with combinations of low-dose CBD and THC.  

If these data are true, CBD and CBDA, especially in a full-spectrum or whole-plant product, could help prevent cognitive decline and neurodegenerative diseases as you get older.

HOW TO PROTECT YOUR MENTAL HEALTH AS YOU AGE

As we mentioned earlier, lifestyle factors like sleep, stress, and alcohol use often have a bigger impact on adult cognition than cannabis. The good news is, these are things you can actually control. Here are a few ways to protect your mental health as you get older:

1. Sleep Well: Your brain needs deep, restorative rest to clear out toxins and store memories. Aim for 7 to 9 hours most nights.
2. Stay hydrated: Keep your brain and body well-lubricated to help clear metabolic buildup and toxins by drinking enough water daily – and 8 cups a day isn’t enough anymore. Aim to drink 15.5 cups (3.7L) for biological men, and 11.5 cups (2.7L) for biological women. 
3. Minimize Stress: Anxiety and chronic stress are silent killers that gradually wear out your brain and body. Practices like meditation, deep breathing, or even a daily walk can make a big difference.
4. Stay Physically Active: Exercise boosts blood flow to the brain and helps build resilience against cognitive decline.
5. Eat More Brain-Friendly Foods: Foods rich in omega-3s, antioxidants, and whole grains like fish, berries, nuts, and leafy greens can support long-term brain health.
6. Take Less Alcohol: Too much drinking takes a toll on memory and cognition, so moderation is key.
7. Avoid smoking or quit tobacco: Smoking and tobacco use are linked to cognitive decline, impairment, and dementias like Alzheimer’s. Fortunately, the cognitive outcomes are favorable the sooner you quit smoking.
8. Be Mindful with Cannabis: If you have concerns about THC affecting your memory or focus, pair it with an equal dose of CBD or switch altogether to CBD-dominant products like hemp or CBD distillates. CBD shows promise for supporting brain health and even mitigates THC’s impairing effects without causing intoxication by itself.
9. Stay Socially Connected: Strong relationships and regular social interaction help protect against depression and cognitive decline. Blue zone areas are good evidence of this.
10. Keep Your Mind Engaged: Learning new skills, languages, reading, puzzles, or even playing strategy games can help keep your brain sharp. Minimize passive activities like TV or movies.

READ: The Pros and Cons of Cannabis Use: Health Insights

FAQs

At what age is it safe to use cannabis?

There’s a risk of cannabis affecting cognitive development in not-yet-fully-developed brains. For your safety, it’s best to wait until at least 25 years old, which is typically when the brain fully matures. However, the most recent data challenges this, suggesting that use between 18-25 is no different from 25 and above.

What type of cannabis is least likely to affect my intelligence long-term?

A CBD-rich or CBG-rich hemp-derived cannabis product is least likely to affect intelligence long-term, since it doesn’t impair cognition like THC. 

If you like using THC, try pairing it with an equal dose of CBD, CBG, or even acidic forms like THCA and CBDA to maximize brain and sleep architecture preservation.

Is cannabis bad for the brain?

Not in general, but it depends on how, when, and how much you use. Prolonged and heavy use in adolescents before age 16 may affect memory and learning in later years. Currently, data suggest no long-term harm in ages 18-25 or 25+. 

On the other hand, adults using CBD-dominant products may experience reduced brain inflammation and potentially improved cognitive function over time. Acidic, whole-plant cannabinoids like THCA and CBDA are also likely cognitive-beneficial and non-intoxicating.

How long does cannabis make you forgetful?

THC may affect memory and attention for a few hours while you’re high, making you forgetful. Your mental sharpness should return to normal once the high fades.

Why do stoners think they’re smart?

Stoners often feel smarter because THC alters perception, making ordinary thoughts seem profound. The high boosts confidence and may spark novel thoughts and ideas that feel brilliant in the moment.