Brain Damage Observed for Smokers

 

People who smoke high-potency pot show signs of damage in a key part of their brain. The results of the new study, however, are limited. The brain scanning study was small. And it doesn’t show that marijuana caused the brain abnormality — only that the two go hand-in-hand.

But the finding suggests that potency matters, says Tiago Reis Marques. This coauthor of the study is a psychiatrist at King’s College London, in England. His team published its findings online November 27 in Psychological Medicine.

Just as vodka packs more of a punch than beer, a high-potency toke of cannabis — the name for the marijuana plant — delivers much more of the brain-active substance THC. That’s an abbreviation for tetrahydrocannabinol (TEH-trah-hy-drow-ka-NAB-ih-nol). It’s possible, Reis Marques says, that a bigger dose of THC simply may have stronger effects on the brain.

That’s important because as breeders have been improving their marijuana plants, THC levels have soared. Samples sold in Colorado, for instance, now have about three times as much THC as plants grown 30 years ago, a recent survey found.

The new study asked 43 healthy people to give a detailed history of their past drug use. About half said they smoke pot. These people then reported how potent that marijuana was. Reis Marques and his colleagues then scanned the brains of all participants. They used a method called diffusion tensor imaging. It shows the structure of white matter — neural highways that carry messages between different brain areas.

The corpus callosum — white matter linking the left brain to the right — is leakier in people who smoke high-potency pot, a new study finds. 

TAbildskov/Wikimedia Commons (CC BY-SA 3.0)

People who reported using high-potency marijuana showed signs of damage in the corpus callosum. This is the major white matter tract that connects the left side of the brain to the right. Water molecules in the damaged corpus callosum diffused more easily than normal, a sign that its tissue had weakened.
This suggests a link between smoking high-potency pot and white-matter damage. But the study can’t prove that cannabis was to blame. “These people could have had deviant brain structures prior to use,” says Mitch Earleywine. He’s a psychologist of the University at Albany in New York. He also serves on the advisory board of NORML. (That’s the National Organization for the Reform of Marijuana Laws.) The new results might also be due to use of other mind-altering drugs, he says. Cocaine, for instance, has been tied to changes in the corpus callosum, notes Earleywine.

Because the experiment looked only at brain structures, it’s unclear whether these changes would affect brain function. For instance, there are no data on whether these changes were linked to memory problems, impulsive behaviors or depression.

It’s also not known whether pot’s THC content affects white matter elsewhere in the brain, says Hans Breiter. He’s a neuroscientist and psychiatrist at Northwestern University in Evanston, Ill. “This study leaves out what is occurring with the rest of the white matter,” he says. It will be important to look at other parts of the brain, he says. He’s particularly interested in possible impacts on regions linked to memory and other behaviors that marijuana might affect.

With the growing legal availability of supercharged marijuana, understanding exactly what it does to the brain is more important than ever, Reis Marques says. This is particularly true, he argues, for young people. They may not realize the marijuana they are using may be much more powerful than ever before. “We are in a stage where there is missing [health effects] information, or the information is changing fast,” he says.

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