Regular marijuana use bad for teens’ brains

Marijuana (stock image).
Credit: © riccardo bruni / Fotolia

We, at ZME Science, have written about a lot of marijuana studies. Personally, having reported quite a few of them, I feel that marijuana has a pretty significant medicinal potential. For starters, it can mitigate the symptoms of diseases such as Parkinson’s, it can offer significant pain relief, and it can even make you thinner. There are even some theories of marijuana usage to actually treat cancer, but we are still in the initial phases of those studies. Furthermore, it seems fairly clear that its effects don’t really justify its classification as a drug, as it is much more resembling to something like alcohol. But marijuana shouldn’t be idealized (and I have seen this worrying trend), as it also has significant negative effects. For starters, it doesn’t always provide pain relief – sometimes it prolongs and accentuates pain. Heavy marijuana users also have poor memory and abnormal brain structure, and smoking while pregnant is a definite no-no. Now, researchers have also shown that heavy marijuana consumption in teens can also damage the brain, causing cognitive decline, poor attention and memory, and decreased IQ.

“It needs to be emphasized that regular cannabis use, which we consider once a week, is not safe and may result in addiction and neurocognitive damage, especially in youth,” said Krista Lisdahl, PhD, director of the brain imaging and neuropsychology lab at University of Wisconsin-Milwaukee.

Marijuana use is increasing in the developed world. In 2012, a study showed that 6.5 percent of high school seniors in the US reported smoking marijuana daily, up from 2.4 percent in 1993. However, while casual, irregular consumption has few downsides, constant marijuana intake can have significant negative impacts. A longitudinal study on 1,037 participants concluded that teens who consume marijuana regularly lose an average of six points of IQ when they reach adulthood. This study found similar implications.

Researchers used brain imaging techniques to see how the brain of regular marijuana users evolve over time, focusing on teens. Abnormalities in the brain’s gray matter, which is associated with intelligence, have been found in 16- to 19-year-olds who increased their marijuana use in the past year, they report. These findings remained even after compensating for major medical conditions, prenatal drug exposure, developmental delays and learning disabilities.

“When considering legalization, policymakers need to address ways to prevent easy access to marijuana and provide additional treatment funding for adolescent and young adult users,” she said. She also recommended that legislators consider regulating levels of tetrahydrocannabinol, or THC, the major psychoactive chemical in marijuana, in order to reduce potential neurocognitive effects.

Indeed, the tendency has been for the THC level to rise in marijuana plants, and this could be one of the major causes of these negative effects.


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  1. Pingback: Marijuana use among teenagers drops to lowest since 1994, despite widespread legalization | Responsible Cannabis Legislation Association | Utah

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