Marijuana Changes Your Brain, but Not Forever

By Dirk Hanson 06/08/11

Can the brain recover from chronic weed smoking? Neural plasticity—the brain’s ability to rewire itself—means that some of the changes caused by heavy drug use are reversible.

Brain Recovery After Quitting Weed
Maybe too late for this guy.
Photo via thinkstockphotos

A recent paper on work done by NIDA scientists, including Director Nora Volkow, featured PET scan imaging of CB1 receptors—the brain's major receptors for cannabis. The crux of their findings was that like every other drug, heavy and continual use results in a net loss of neuro-receptor availability and quantity. To put it another way, what goes up must come down. If your drug of choice is cocaine, for example, then your immediate problem in withdrawal is a howling lack of available dopamine, one of the so-called pleasure chemicals in the brain. The net result: you feel like crap. How bad your comedown is, and how long it takes the brain to readjust itself, generally depends on how long and strong the addiction has been.

The study involved 30 serious stoners in an inpatient facility, who were monitored with PET scans for about four weeks. In the case of regular marijuana addicts (admittedly a small fraction of the total user population), overall CB1 receptor density was 20% lower in heavy regular pot smokers, compared to control subjects who rarely smoked the ganja. Heavy smokers who submitted to a second PET scan after a month of abstinence showed a marked increase in receptor activity "in those areas that had been decreased at the outset of the study.” This is exactly the sort of brain plasticity that scientists commonly see in withdrawal and abstinence—a sign of the brain normalizing its functions in the absence of the drug. In fact, the NIDA researchers admit as much, noting that “while chronic cannabis smoking inhibits CB1 receptors, the damage is reversible with abstinence.” Neural plasticity—the brain’s ability to rewire itself—means that some of the changes caused by addictive drugs are reversible. Another word for that process is recovery.

It’s an interesting study,  not because the finding is novel—it would be a miracle if heavy dope smoking did not alter CB1 receptor distributions in some way. Instead the study bolsters the notion that marijuana withdrawal is similar to other withdrawals due to biochemical similarities in how these drugs work. So if you see any scare stories aabout marijuana’s “adverse effects” on regular users, remember that “damage” doesn’t necessarily mean “permanent damage.” Because if it did, a whole lot more of us would be missing in action….

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Dirk Hanson, MA, is a freelance science writer and the author of The Chemical Carousel: What Science Tells Us About Beating Addiction. He is also the author of The New Alchemists: Silicon Valley and the Microelectronics Revolution. He has worked as a business and science reporter for numerous magazines and trade publications including Wired, Scientific American, The Dana Foundation and more. He currently edits the Addiction Inbox blog. Email: [email protected]