Imagine a not-so-distant future: You’re at a Lakers game in L.A.’s Staples Center. Everyone in the stadium is high. The team, by some miracle, is winning, yet its fans — who have been smoking legally for years now, maybe decades — aren’t satisfied. They’re bored; they even feel a little angry. Instead of getting pumped to the “defense song,” there’s a collective decision to smoke another blunt. While this may sound like a paranoid anti-marijuana PSA, science suggests it also could be a realistic look at the future.

According to a new review of cannabis research in Nature, something that researchers are seriously concerned about is the fact that marijuana — used over many years — can lower dopamine levels. This, in turn, can reduce motivation and induce negative emotions.

Understanding how marijuana affects the brain is “a pressing concern for global health.”
Understanding how marijuana affects the brain is "a pressing concern for global health."

In a press release issued Thursday, the researchers, from Imperial College London, argue that the steady spread of marijuana legalization means that it’s more important than ever to determine the long-term effects of smoking weed. Their review highlights the “conclusive evidence” that cannabis decreases dopamine levels. What they call for now is more research to understand exactly how this happens.

This is critical to understand because of the health implications for smokers. The researchers write that heavy cannabis use is “associated with an increased risk of mental health disorders such as psychosis, addiction, depression, and suicide.”

“The changing patterns of cannabis use, including ‘cannavaping’ and edible products, means it’s vital that we understand the long-term effects of cannabis on the brain,” says co-author Michael Bloomfield, Ph.D. “This new research helps to explain how people get people addicted to cannabis, by showing that one if its main components, called THC, alters a delicate balance of brain chemicals.”

THC (tetrahydrocannabinol) is the main psychoactive ingredient in cannabis and mimics a naturally occurring brain chemical called anandamide. A little bit of THC triggers an increase in dopamine release and neuron activity. Long-term THC exposure is, the researchers believe, what causes a blunting of the dopamine system.

Scanned brains of long-term cannabis users.
Scanned brains of long-term cannabis users.

Currently, THC levels in cannabis are the strongest they’ve ever been. In the 1970s, the average THC level was 8 percent. Today, different strains have THC levels anywhere between 18.7 to 30 percent. These high levels, the researchers argue, makes it even more urgent to understand cannabinoid-dopamine interactions and how they affect the mental health of smokers. In their review, they call for further animal studies on this interaction as well as studies on the brains of adolescents that consume cannabis as they mature into adulthood. There’s an understanding that long-term smoking creates this effect, but there’s little agreement on how long “long-term” really is.

“We urgently need to better understand how cannabis affects the brain, to help policy makers and individuals make informed decisions,” says psychiatrist Oliver Howes, Ph.D., who led the review. “If it turns out that it’s bad news to take cannabis then we need to know now, before people take the gamble.”

And now that weed is legal in California, it’s likely that Los Angelenos are likely to “take the gamble” pretty soon. With the probability that long-term smoking will decrease motivation and dampen mood, having a losing basketball team won’t be the only thing making Lakers fans depressed.

Photos via Giphy (1, 2), MRC CSC, Flickr / victoriabernal