Science Weed is harming teens’ brain development, largest US study warns

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By Rachel Sacks Published May 3, 2026, 10:19 a.m. ET

A new study has found sobering effects of weed on teenage brains.

While more teens are staying away from marijuana across the country, the drug is still used by one in five kids in New York, according to a New York Impact Report from November 2025.

And though some purport the substance can improve mood and energy, there are negative effects on cognitive skills — especially in younger users.

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While marijuana use hasn’t risen amongst teens, a large study has found the substance has a major impact on the brain.

Researchers from the University of California San Diego (UC San Diego) have conducted the largest long-term study in the US on cannabis use in kids.

Analyzing more than 11,000 children from ages 9 to 17, the team tracked both substance use and cognitive performance through self-reporting and biological testing.

Across a range of skills including memory, attention, language and processing speed, teens who used cannabis showed restricted growth during key years of brain development.

Progress in memory, focus and thinking speed leveled off as they got older and started using cannabis compared to their peers who didn’t.

And in smaller groups of participants, those exposed to THC had worsened memory over time, while CBD didn’t have the same effect.

Although the differences were modest, researchers say they’re still important as they occurred during a crucial time of growth.

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Teens who used cannabis had slower brain development, including memory, focus and processing speed. David – stock.adobe.com

“These differences may seem small at first, but they can add up in ways that affect learning, memory and everyday functioning,” lead study author and assistant professor in the Department of Psychiatry at UC San Diego School of Medicine Natasha Wade said in a press release.

“[The result] also highlights how complicated cannabis products can be, especially since some products labeled as CBD may still contain THC,” Wade added.

These findings come after marijuana poisoning cases have skyrocketed 56% among New Yorkers under 19, according to data from the National Poison Data System cited in the impact report.

Meanwhile, edible use has also skyrocketed as more teens unknowingly consumed large quantities of cannabis.

And from the National Poison Data System findings, more than 95% of poisoning cases in teens were caused by edibles.

The UC San Diego team will continue looking at the effects of weed on teens to understand the long-term effects, including timing and frequency, as the original participants transition into young adulthood.

Researchers suggest that delaying cannabis use could play a role in healthier brain development.

“As cannabis becomes more widely available, it’s important for families and teens to understand how it may affect the developing brain,” Wade said.
L|A
 
Weed makes you lazy and stupid, who'd have thunk.

Wonder why The State stopped having a problem with it? Maybe they wanted more shekels, and maybe the goyim needed to be dumbed down a tad, a lot of them are asking too many anti-semitic questions.
 
I smoked weed underage - I wasn’t anywhere near what you’d call a stoner (I didn’t have the cash for it if I wanted to anyways) and I also drank.

It’s not ideal for anyone but it can be especially damaging for some.

The scare tactics don’t work on kids. If you tell them taking a hit off a joint is going to turn them into a junkie or a loser they’re going to see that’s not necessarily the case and then they’ll question what else you’ve told them that really matters.

Tell them the truth that the shit’s overrated, expensive and will get them into potential legal troubles.
 
Tell them the truth that the shit’s overrated, expensive and will get them into potential legal troubles.
That kind of message is useful for a lot of things you want teenagers to not do, or at least do less. Drinking, vaping, sex, what have you. Also if you tell them that people won't really think they're cool.
 
I smoked weed underage - I wasn’t anywhere near what you’d call a stoner (I didn’t have the cash for it if I wanted to anyways) and I also drank.

It’s not ideal for anyone but it can be especially damaging for some.

The scare tactics don’t work on kids. If you tell them taking a hit off a joint is going to turn them into a junkie or a loser they’re going to see that’s not necessarily the case and then they’ll question what else you’ve told them that really matters.

Tell them the truth that the shit’s overrated, expensive and will get them into potential legal troubles.

Wouldn't the Singapore route of caning your kids for smoking be more effective? Those countries that have the death penalty for drug trafficking are still safer (as of now) than countries that are letting stoners off more easily.

And does China still ban weed, or are they also lessening punishments for it too?
 
Wouldn't the Singapore route of caning your kids for smoking be more effective? Those countries that have the death penalty for drug trafficking are still safer (as of now) than countries that are letting stoners off more easily.

And does China still ban weed, or are they also lessening punishments for it too?

1. Singapore still has a drug trade.
2. Corporal punishment only works on certain children. Every shit bird criminal in America had some legal guardian who beat them at some point.
 
I smoked weed underage - I wasn’t anywhere near what you’d call a stoner (I didn’t have the cash for it if I wanted to anyways) and I also drank.

It’s not ideal for anyone but it can be especially damaging for some.

The scare tactics don’t work on kids. If you tell them taking a hit off a joint is going to turn them into a junkie or a loser they’re going to see that’s not necessarily the case and then they’ll question what else you’ve told them that really matters.

Tell them the truth that the shit’s overrated, expensive and will get them into potential legal troubles.
Bring an average stoner to the schools, maybe make sure he is especially TDS afflicted for maximum cringe.
 
That kind of message is useful for a lot of things you want teenagers to not do, or at least do less. Drinking, vaping, sex, what have you. Also if you tell them that people won't really think they're cool.
My first job as a teenager was in a shop that sold a lot of cigarettes and lottery tickets. Seeing how much money people dropped on both of those, often daily, sometimes even multiple times a day, put me off both for life. Especially as you'd sometimes see people who were genuinely desperate for their cigarettes/scratch cards, in a way that was honestly kind of repulsive.
 
I'm very happy I never really got into smoking weed when I was a teen. It was boring being around people who were more or less chronic smokers who's main hobby was smoking a bowl and playing GTA all day. There is nothing worse than people carry this on into their adulthood.
 
That kind of message is useful for a lot of things you want teenagers to not do, or at least do less. Drinking, vaping, sex, what have you. Also if you tell them that people won't really think they're cool.

Personally anything that could permanently damage my brain function is enough to not make me touch it - experts are still undecided about brain cells being able to regenerate but the general consensus seems to be "nope" despite the optimistic articles that pop up every now and again.

Anyone who keeps peddling the "it's not really harmful" mantra should be taken behind a shed or beaten with a large stick so that they quickly learn not to spread their poison to more impressionable youngsters with precious, developing minds.

Those cringey 90s cartoons with Winnie The Pooh and Ninja Turtles really were on to something.
 
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