Chronic Marijuana Use Shrinks Brain, Study Finds

30 Jan Chronic Marijuana Use Shrinks Brain, Study Finds

The brains of habitual marijuana users grow smaller over time, particularly in an area that influences the odds that they will get addicted, a new study finds.

Marijuana is an increasingly popular mind-altering drug used for both recreational and limited medicinal purposes. Researchers have known for some time that habitual consumption of this drug can trigger significant changes in brain function, including the onset of marijuana/cannabis addiction. In a study published in November 2014 in the Proceedings of the National Academy of Sciences, a team of American researchers examined the long-term impact that habitual marijuana intake can have on the brain’s structure.

Marijuana Use Figures

Approximately 19.8 million Americans over the age of 11 use marijuana in any given month, according to the 2013 results of a federally sponsored, large-scale project known as the National Survey on Drug Use and Health (NSDUH). This number is the equivalent of roughly 7.5 percent of the U.S. population age 12 or older. Marijuana intake across the country increased by a statistically insignificant amount between 2012 and 2013; however, the 2013 figures continue an overall upward trend in the drug’s use that started in the early 2000s.

Nationwide rates for marijuana use far outstrip the rates of use for any other illicit/illegal drugs or medications. In terms of age, the peak rates of monthly use occur among young adults between the ages of 18 and 25. Eighteen- to 20-year-olds have the highest overall rate (22.6 percent), while 21- to 25-year-olds have the second-highest rate (20.9 percent). In 2013, the rate of marijuana consumption fell somewhat among 18- to 20-year-olds and increased somewhat among 21- to 25-year-olds. Statistically speaking, people between the ages of 12 and 17 and people over the age of 25 use marijuana less than half as often as people between the ages of 18 and 25.

Known Effects on the Brain

In the short-term, marijuana produces substantial changes in parts of the brain responsible for doing such things as recording and recalling memories, focusing attention, controlling appetite, interpreting information coming in from the five senses, controlling body balance, controlling muscle coordination and reacting to physical changes in the local environment. When consumed in large amounts (which grow smaller as the potency of the drug increases over time), marijuana can also trigger severe symptoms of psychosis. In the long-term, roughly one-quarter to one-half of habitual marijuana users will undergo the changes in brain function that mark the presence of cannabis dependence/addiction. These changes center on a part of the brain known informally as the pleasure center. In addition, marijuana use may have a lasting impact on the brain development of people who start consuming the drug as preteens or teenagers.

Newly Identified Marijuana Consequences

In the study published in the Proceedings of the National Academy of Sciences, researchers from the University of Texas at Dallas, the University of New Mexico and the Mind Research Center used MRI (magnetic resonance imaging) brain scanning technology to assess the structural brain changes brought about by a long-term pattern of marijuana intake. The researchers also used cognitive tests to assess the functional brain changes brought about by such a pattern of intake. A total of 110 adults took part in this project; 48 of the study participants were active marijuana consumers, while the remaining 62 participants were a control group of individuals not involved in marijuana use. The marijuana-using participants typically consumed the drug multiple times per day.

The researchers concluded that the brain size of long-term users decreases over time, particularly in an area that influences the odds that a consumer of the drug will become  addicted. They also concluded that the brain tries to offset marijuana-related size deficits by increasing the number of connection points that link various brain areas together. For a number of years, this compensation process can essentially mask the impact of long-term marijuana intake. However, continued use of the drug will eventually overtax the brain’s compensating abilities.

When the researchers compared the cognitive testing outcomes of the habitual marijuana users to the outcomes of the non-marijuana users, they concluded that the consumers of the drug had substantially lower IQ scores. However, the researchers could not systematically link the structural brain changes associated with habitual marijuana use to the observed IQ deficits. Overall, the study’s authors believe that two main factors appear to influence the structural and functional problems associated with habitual consumption of the drug: the age at which this consumption begins and the length of time it continues.

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